JP2003249686A - Light emitting diode driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting diode driving circuit capable of contributing stability of brightness of a light emitting diode and improvement of power efficiency. <P>SOLUTION: When operation of a constant current circuit 13 is controlled so as to be turned on by a switching element Q7 in accordance with a pulse signal from the external, a current mirror circuit 15 is started by a starting resistor R2 to generate a current, which is received by a band gap circuit 17 to generate a constant current having a positive temperature coefficient, and the constant current is supplied to an LED1 connected to the switching element Q7 and the constant current circuit 13 in series. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode drive circuit for driving a light emitting diode (hereinafter referred to as LED) with a constant current.

[0002]

2. Description of the Related Art Conventionally, as a light emitting diode drive circuit, those shown in FIGS. 15 and 17 are known. The LED drive circuit 101 shown in FIG. 15 includes a DC power supply Vcc, a resistor R101, and a transistor Q101. As shown in FIG. 16, when the pulse signal input from the outside to the point A becomes low level and the LED 101 is turned off, the drive current of the LED 101 can be cut off, which enables high-efficiency drive. It has the advantage that

The LED drive circuit 102 shown in FIG.
Is composed of a DC power source Vcc, a constant current source (transistors Q102 and Q103) composed of a current mirror circuit, and a transistor Q104. This LED drive circuit 10
When a plurality of LEDs 102 are provided and the LEDs 102 having the same luminous intensity rank are mounted on each LED, the brightness does not vary even if the forward voltage VF of each LED 102 varies.

As the LED drive circuit, the circuit described in Patent Document 1 has been reported.

[0005]

[Patent Document 1] JP-A-6-209123

[0006]

However, as shown in FIG.
When a plurality of LED drive circuits 101 shown in FIG.
Since the forward voltage VF of the LED 101 varies, the forward current IF changes and the operating point is different.
There was a problem that the brightness was likely to be different for each.

Further, the LED drive circuit 102 shown in FIG.
Then, as shown in FIG. 18, even if the pulse signal input from the outside to the point B becomes high level and the LED 102 is turned off, a constant current flows in the transistor Q104.
There was a problem that the power supply efficiency was lowered. For this reason,
It has been desired to realize an LED drive circuit that can operate with high efficiency using a constant current circuit.

The present invention has been made in view of the above,
An object of the present invention is to provide a light emitting diode drive circuit which can stabilize the brightness of the light emitting diode and contribute to the improvement of power supply efficiency.

[0009]

The invention according to claim 1 is
To solve the above problems, a constant current circuit that supplies a constant current having a positive temperature coefficient to a light emitting diode, and a pulse signal from the outside that is connected in series to the light emitting diode and the constant current circuit connected in series A switching element that controls the operation of a constant current circuit according to the above, and a light emitting diode drive circuit comprising the constant current circuit, wherein the constant current circuit activates the current mirror circuit as a current source and the current mirror circuit. And a bandgap circuit that receives a current generated from the current mirror circuit and generates a constant current having a positive temperature coefficient.

In order to solve the above problems, the present invention provides a constant current circuit for supplying a constant current having a negative temperature coefficient to a light emitting diode, and the light emitting diode and the constant current circuit connected in series. A light emitting diode drive circuit comprising: a switching element connected in series to control ON / OFF of an operation of a constant current circuit according to a pulse signal from the outside, wherein the constant current circuit is a current mirror as a current source. A circuit, a starting resistor for starting the current mirror circuit, a reference voltage circuit for receiving a current generated from the current mirror circuit to generate a reference voltage and a constant current having a negative temperature coefficient, It is a gist to have.

According to a third aspect of the present invention, in order to solve the above problems, a constant current circuit for supplying a constant current having a temperature coefficient of a predetermined sign and magnitude to the light emitting diode, and the light emitting diode connected in series. And a switching element that is connected to the constant current circuit in series and controls ON / OFF of the operation of the constant current circuit according to a pulse signal from the outside, and the constant current circuit is a current control circuit. A current mirror circuit as a source, a starting resistor for starting the current mirror circuit, and a current generated from the current mirror circuit to generate a reference voltage and a constant current having a negative temperature coefficient. A reference voltage circuit and a bar for receiving a constant current generated from the reference voltage circuit and generating a constant current having a temperature coefficient of a predetermined sign and magnitude. And summarized in that having a-gap circuit.

According to a fourth aspect of the present invention, in order to solve the above problems, in the constant current circuit, the current mirror circuit has PNP type first and second transistors, and the emitters are commonly connected. The bases are commonly connected,
Further, the base-collector of the second transistor is connected, the bandgap circuit has NPN-type third and fourth transistors, the bases of which are commonly connected, and the collector and the third of the first transistor are connected. The collector and the base of the transistor are connected, the collector of the second transistor and the collector of the fourth transistor are connected, the emitter of the third transistor is connected to one end of the first resistor, and the emitter of the fourth transistor is connected. Is the first
The starting resistance is connected between the base of the second transistor and one end of the first resistance.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problems, in the constant current circuit, the current mirror circuit has first and second PNP type transistors, and emitters are commonly connected. The bases are commonly connected,
Further, the base-collector of the second transistor is connected, and the reference voltage circuit has third and fourth NPN-type transistors, the bases of which are commonly connected, and the first voltage
The collector of the third transistor is connected to the collector and the base of the third transistor, the collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected through at least one diode. Connected to one end of the first resistor,
The emitter of the fourth transistor is connected to the other end of the first resistor, and the starting resistor is connected between the base of the second transistor and one end of the first resistor. To do.

According to a sixth aspect of the present invention, in order to solve the above-mentioned problems, in the constant current circuit, the current mirror circuit has first and second PNP type transistors, and their emitters are commonly connected. The bases are commonly connected,
Further, the base-collector of the second transistor is connected, and the reference voltage circuit has third and fourth NPN-type transistors, the bases of which are commonly connected, and the first voltage
The collector of the transistor and the collector and the base of the third transistor are connected, the collector of the second transistor and the collector of the fourth transistor are connected, and the emitter of the third transistor is connected in series. The first diode of the diode is connected to the anode, the emitter of the fourth transistor is connected to the other end of the first resistor, the bandgap circuit has NPN type fifth and sixth transistors, The bases are commonly connected, one end of the first resistor is connected to the collector and the base of the fifth transistor, the emitter of the second transistor is connected to the collector of the sixth transistor, and the emitter of the fifth transistor is connected. Is connected to the other end of the third resistor, and the emitter of the sixth transistor is connected to one end of the third resistor. Is connected to the cathode of the mth diode of the m diodes connected in series, and the starting resistor is connected between the base of the second transistor and one end of the third resistor. That is the summary.

In order to solve the above-mentioned problems, the invention according to claim 7 is characterized in that the fourth transistor provided in the bandgap circuit has a multi-emitter.

In order to solve the above-mentioned problems, the invention according to claim 8 is characterized in that the sixth transistor provided in the bandgap circuit has a multi-emitter.

According to a ninth aspect of the invention, in order to solve the above-mentioned problems, the first resistor and the third resistor have the fourth resistance.
The gist of the present invention is to limit the current flowing through the transistor and the fifth transistor and adjust the temperature coefficient of the current flowing through the sixth transistor.

In order to solve the above-mentioned problems, the tenth aspect of the invention is to provide the switching element, which is a semiconductor switching element formed of any one of a piper transistor, an FET, and an IGBT.

In order to solve the above-mentioned problems, the gist of the present invention is to form a monolithic semiconductor integrated circuit.

According to a twelfth aspect of the present invention, in order to solve the above-mentioned problems, a constant current circuit for supplying a constant current having a positive temperature coefficient to the light emitting diode is provided, and the light emitting diode and the constant current circuit are connected in series. In the light emitting diode drive circuit, the constant current circuit receives a current mirror circuit as a current source, a starting resistor for starting the current mirror circuit, and a current generated from the current mirror circuit. And a bandgap circuit that generates a constant current having a positive temperature coefficient.

According to a thirteenth aspect of the invention, in order to solve the above-mentioned problems, a constant current circuit for supplying a constant current having a negative temperature coefficient to the light emitting diode is provided, and the light emitting diode and the constant current circuit are connected in series. In the light emitting diode drive circuit, the constant current circuit receives a current mirror circuit as a current source, a starting resistor for starting the current mirror circuit, and a current generated from the current mirror circuit. And a reference voltage circuit that generates a constant voltage having a negative temperature coefficient.

In order to solve the above-mentioned problems, a fourteenth aspect of the present invention comprises a constant current circuit for supplying a constant current having a temperature coefficient of a predetermined sign and magnitude to the light emitting diode,
A light emitting diode drive circuit comprising the light emitting diode and the constant current circuit connected in series, wherein the constant current circuit includes a current mirror circuit as a current source, and a starting resistor for starting the current mirror circuit. A reference voltage circuit that receives a current generated from the current mirror circuit to generate a reference voltage and a constant current having a negative temperature coefficient; and a predetermined voltage that receives a constant current generated from the reference voltage circuit. And a bandgap circuit for generating a constant current having a temperature coefficient of sign and magnitude.

In order to solve the above-mentioned problems, the fifteenth aspect of the invention is summarized as being monolithically formed as a semiconductor integrated circuit.

According to a sixteenth aspect of the present invention, in order to solve the above-mentioned problems, an on / off control circuit that alternately generates a start trigger and a stop signal according to a pulse signal from the outside, and an on / off control circuit are connected in series to a light emitting diode. Moreover, a start trigger and a stop signal are input from the on / off control circuit, and a constant current is supplied to the light emitting diode in response to the start trigger, while a constant current supplied to the light emitting diode in response to the stop signal is supplied. The gist is that a constant current circuit for stopping is provided.

In order to solve the above problems, the constant current circuit inputs a start trigger and a stop signal from a current mirror circuit for supplying a constant current to the light emitting diode and the on / off control circuit. Then, in response to the activation trigger, the current generated by the current mirror circuit is received to start generating a constant current having a positive temperature coefficient, while the constant current is supplied to the current mirror circuit according to the stop signal. And a bandgap circuit for stopping the operation.

To solve the above problems, the constant current circuit inputs a start trigger and a stop signal from a current mirror circuit for supplying a constant current to the light emitting diode and the on / off control circuit. The current mirror circuit receives the current generated by the current mirror circuit in response to the start trigger to generate a reference voltage and starts generating a constant current having a negative temperature coefficient, while the current mirror circuit operates in response to the stop signal. The gist is to have a reference voltage circuit for stopping the supply of a constant current in the circuit.

In order to solve the above problems, the constant current circuit inputs a start trigger and a stop signal from a current mirror circuit for supplying a constant current to the light emitting diode and the on / off control circuit. The current mirror circuit receives the current generated by the current mirror circuit in response to the start trigger to generate a reference voltage and starts generating a constant current having a negative temperature coefficient, while the current mirror circuit operates in response to the stop signal. A reference voltage circuit for stopping the supply of a constant current to the circuit; and a bandgap circuit for receiving a constant current generated from the reference voltage circuit and generating a constant current having a temperature coefficient of a predetermined sign and magnitude. Is the gist.

In order to solve the above-mentioned problems, an on-off control circuit for generating a lighting signal and a stop signal, which are alternately repeated according to a pulse signal from the outside, is provided.
While being connected in series to the light emitting diode, and inputting a lighting signal and a stop signal from the on / off control circuit, and supplying a constant current to the light emitting diode according to the lighting signal,
The gist of the present invention is to provide a constant current circuit for stopping the constant current supplied to the light emitting diode according to the stop signal.

In order to solve the above-mentioned problems, the constant current circuit inputs a lighting signal and a stop signal from a current mirror circuit for supplying a constant current to the light emitting diode and the on / off control circuit. Then, in response to the lighting signal, the current generated by the current mirror circuit is received to start generating a constant current having a positive temperature coefficient, while the constant current is supplied to the current mirror circuit according to the stop signal. And a bandgap circuit for stopping the operation.

In order to solve the above problems, the constant current circuit inputs a lighting signal and a stop signal from a current mirror circuit for supplying a constant current to the light emitting diode and the on / off control circuit. The current mirror circuit receives the current generated by the current mirror circuit in response to the lighting signal to generate a reference voltage to start generating a constant current having a negative temperature coefficient, while the current mirror circuit operates in response to the stop signal. The gist is to have a reference voltage circuit for stopping the supply of a constant current in the circuit.

In order to solve the above problems, the constant current circuit inputs a lighting signal and a stop signal from a current mirror circuit for supplying a constant current to the light emitting diode and the on / off control circuit. The current mirror circuit receives the current generated by the current mirror circuit in response to the lighting signal to generate a reference voltage to start generating a constant current having a negative temperature coefficient, while the current mirror circuit operates in response to the stop signal. A reference voltage circuit for stopping the supply of a constant current to the circuit; and a bandgap circuit for receiving a constant current generated from the reference voltage circuit and generating a constant current having a temperature coefficient of a predetermined sign and magnitude. Is the gist.

According to a twenty-fourth aspect of the present invention, in order to solve the above-mentioned problems, in the constant current circuit, the current mirror circuit has first and second PNP type transistors, and their emitters are commonly connected. The bases are commonly connected, the base-collector of the second transistor is further connected, and the bandgap circuit has NPN-type third and fourth transistors, the bases are commonly connected, and the first transistor is connected. Is connected to the collector and the base of the third transistor, the collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected to one end of the first resistor, The gist is that the emitter of the fourth transistor is connected to the other end of the first resistor.

In order to solve the above problems, the present invention provides a constant current circuit, wherein the current mirror circuit has first and second PNP type transistors, and emitters are commonly connected. The bases are commonly connected, the base-collector of the second transistor is further connected, the reference voltage circuit has third and fourth NPN-type transistors, the bases are commonly connected, and the first transistor is connected. Is connected to the collector and the base of the third transistor, the collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected to at least one diode through at least one diode. Connected to one end of the first resistor, and the emitter of the fourth transistor connected to the other end of the first resistor The gist.

In order to solve the above-mentioned problems, the invention of claim 26 is characterized in that, in the constant current circuit, the current mirror circuit has first and second PNP type transistors, and their emitters are commonly connected. The bases are commonly connected, the base-collector of the second transistor is further connected, the reference voltage circuit has third and fourth NPN-type transistors, the bases are commonly connected, and the first transistor is connected. Is connected to the collector and the base of the third transistor, the collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected in series. Connected to the anode of the first diode, the emitter of the fourth transistor connected to the other end of the first resistor, The bandgap circuit has NPN-type eighth and ninth transistors, the bases of which are commonly connected, one end of the first resistor is connected to the collector and the base of the eighth transistor, and the second transistor is connected. Is connected to the collector of the ninth transistor, the emitter of the eighth transistor is connected to the other end of the fifth resistor, and the emitter of the ninth transistor is connected to the fifth transistor.
It is connected to one end of the resistor and is connected to the cathode of the m-th diode of the m diodes connected in series.

In order to solve the above problems, the on / off control circuit according to the twenty-seventh aspect of the present invention has NPN type fifth, sixth and seventh transistors, and the base of the seventh transistor is externally connected. Pulse signal is input, the power supply is connected to the collector via the third resistance, the emitter is grounded via the fourth resistance, and the connection point between the collector of the seventh transistor and the third resistance is a capacitor. Is connected to the anode of the diode via the, and the cathode of the diode is connected to the base of the fifth transistor, while the connection point between the emitter of the seventh transistor and the fourth resistor is connected to the sixth transistor. A common connection point between the emitters of the first and second transistors of the constant current circuit and the cathode of the light emitting diode, or a source connected to the power supply. Resistor is connected to the collector of the fifth transistor, further, a third collector and the constant current circuit of the common connection point of the first transistor and the collector of the emitter and the sixth transistor of the fifth transistor
The gist is that the collector and the base of the transistor are commonly connected, and the emitter of the sixth transistor is grounded.

In order to solve the above problems, the on / off control circuit according to the twenty-eighth aspect of the present invention has an NPN type seventh transistor, and a pulse signal from the outside is input to the base of the seventh transistor. , The first of the constant current circuit
A starting resistance connected to a common connection point between the emitter of the second transistor and the cathode of the light emitting diode or the power supply is connected to the collector of the seventh transistor, and the collector of the seventh transistor is connected to the first transistor. The gist is that the collector of the transistor is commonly connected to the collector and the base of the third transistor of the constant current circuit, and the emitter of the seventh transistor is grounded.

In order to solve the above problems, the on-off control circuit according to the twenty-ninth aspect of the present invention is a CMOS type seventh circuit.
-1 transistor and 7-2 transistor,
A pulse signal from the outside is input to the commonly connected gates of the 7-1th and 7-2th transistors, and the emitters of the first and second transistors of the constant current circuit are commonly connected to the cathode of the light emitting diode. A point, or a starting resistance connected to a power source is connected to the source of the 7-1th transistor, and further, the drain of the 7-1th transistor and the drain of the 7-2th transistor are commonly connected, The gist is that the collector of the first transistor, the collector and the base of the third transistor of the constant current circuit are commonly connected, and the source of the 7-2th transistor is grounded.

In order to solve the above problems, the thirtieth aspect of the present invention is characterized in that the fourth transistor provided in the band gap circuit has a multi-emitter.

In order to solve the above-mentioned problems, the thirty-first aspect of the present invention is characterized in that the ninth transistor provided in the bandgap circuit has a multi-emitter.

In order to solve the above problems, the thirty-second aspect of the present invention is summarized as being monolithically formed as a semiconductor integrated circuit.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a configuration of an LED drive circuit 11 according to a first embodiment of the present invention.

As shown in FIG. 1, the LED drive circuit 11
Is a constant current circuit 13 that supplies a constant current having a positive temperature coefficient to the LED 1, and a constant current circuit 13 that is connected in series to the LED 1 and the constant current circuit 13 that are connected in series, and that corresponds to a pulse signal from the outside. It is composed of a switching element Q7 for controlling on / off of the operation of No. 13. Specifically, the constant current circuit 13 is the current mirror circuit 1 as a current source.
5, a starting resistor R2 for starting the current mirror circuit 15, and a bandgap circuit 17 for receiving a current generated by the current mirror circuit and generating a constant current having a positive temperature coefficient.

Further, the first resistor R1 is provided to limit the current flowing through the fourth transistor Q4.
In the constant current circuit 13, the current mirror circuit 15 is
It has a PNP type first transistor Q1 and a second transistor Q2, the emitters are commonly connected, the bases are commonly connected, and the base-collector of the second transistor Q2 is further connected. The bandgap circuit 17 has an NPN-type third transistor Q3 and a fourth transistor Q4, the bases of which are commonly connected.
The collector of the first transistor Q1, the collector and the base of the third transistor Q3 are connected, the collector of the second transistor Q2 is connected to the collector of the fourth transistor Q4, and the emitter of the third transistor Q3 is the first Is connected to one end of the resistor R1 and the emitter of the fourth transistor Q4 is connected to the other end of the first resistor R1. Further, the starting resistor R2 is connected to the second transistor Q
It is connected between the base of No. 2 and one end of the first resistor R1.

Next, the operation of the LED drive circuit 11 according to this embodiment of the present invention will be described with reference to FIGS. The time t is the timing shown in FIG. Now, at time t0, the DC power supply Vcc is applied to the LED drive circuit 11, and the description starts with the base voltage of the switching element Q7 being in the low level state.

At this time, since the switching element Q7 is in the off state, no current flows in the LED 1 and the constant current circuit 13. That is, the forward current IF = 0
Has become. Next, at time t1, when the base voltage of the switching element Q7 switches from the low level to the high level, the switching element Q7 switches from the off state to the on state, and the collector of the switching element Q7-
When the emitters are conducting, the voltage at point D shown in FIG.
It becomes D level.

When the voltage at the point D shown in FIG. 1 becomes almost GND level, first, from the DC power supply Vcc, the anode and cathode of LED1, the emitter of the second transistor Q2 to the base, the starting resistor R2, the collector of the switching element Q7 to the emitter. A startup current flows via and it becomes easy to start up. Since the starting resistor R2 has a resistance value on the order of MΩ, the starting current has a value on the order of μA.

In accordance with this starting current, the base voltage at point C shown in FIG. 1 drops and the first and second transistors Q1,
Q2 turns on. It should be noted that the minimum voltage of the DC power supply Vcc that turns on only the first and second transistors Q1 and Q2 of the transistors Q1 to Q4 provided in the constant current circuit 13 is Vcc1 as shown in FIG. Then,

[Equation 1]   Vcc1 = VF (LED1) + VF (Q2)           + {I (R2) × R2} + VCE (satQ7) (1) Becomes

Furthermore, the first and second transistors Q
When Q1 and Q2 are turned on, the third and fourth transistors Q
3, current flows from the base of Q4 to the emitter,
The third and fourth transistors Q3 and Q4 are turned on. As a result, from the DC power supply Vcc to the anode and cathode of LED1, the emitter and collector of the first transistor Q1, the collector and emitter of the third transistor Q3, and the collector and emitter of the switching element Q7, the current I
1 flows. At the same time, a current I2 flows from the DC power source Vcc through the anode and cathode of LED1, the emitter and collector of the second transistor Q2, the collector and emitter of the fourth transistor Q4, the first resistor R1, and the collector and emitter of the switching element Q7. .

All the transistors Q1 to Q4 provided in the constant current circuit 13 are turned on to turn on the IF of the LED1.
The minimum voltage of the DC power supply Vcc that keeps constant is shown in FIG.
As shown in, if Vcc2,

[Equation 2]   Vcc2 = VF (LED1) + VF (Q2) + VCE (Q4)           + (I2 × R1) + VCE (satQ7) (2) Becomes

As described above, the first and second transistors Q1 and Q2 form the current mirror circuit 15, and the current mirror circuit 15 is monolithically formed as a semiconductor integrated circuit. Formed by the first and second transistors Q1, Q
The currents I1 and I2 flowing through 2 are equal.

[0051]

[Equation 3]   I1 = I2 (3) Therefore, the forward current IF flowing in the LED 1 is

[Equation 4]   IF = I1 + I2 (4) Becomes

That is, since the multi-emitter is adopted as the emitter of the fourth transistor Q4, the first resistor R1
By adjusting the above, I1 = I2 is established, and since the first and second transistors Q1 and Q2 are formed in the same cell,

[Equation 5]   I1 = I2 = 0.5 × IF (5) Becomes

Since the emitter area S (Q4) of each fourth transistor Q4 and the emitter area S (Q3) of the third transistor Q3 are formed in the same cell, the fourth transistor Q4 is used. Let n be the number of cells in

[Equation 6]   S (Q4) = n · S (Q3) (6) Becomes

Here, the base of the third transistor Q3
Voltage drop between emitters VBE (Q3) = VBE (Q4) + I
Since the relationship of 2 × R1 holds,

[Equation 7] Becomes

Solving the equation (7), the currents I1, I2, LE
The forward current IF of D1 can be obtained respectively.
The forward current IF generated by the bandgap circuit 17 increases as the junction temperature Tj rises, as shown in FIG.

Thus, at time t1, when the base voltage of the switching element Q7 switches from low level to high level, the switching element Q7 switches from the off state to the on state, and the collector-emitter of the switching element Q7 becomes conductive. As a result, the voltage at point D shown in FIG. 1 becomes almost GND level. As a result, the above-mentioned constant current forward current IF is generated in the LED 1, so that the LED 1 is turned on.

Next, at time t2, when the base voltage of the switching element Q7 switches from the high level to the low level, the switching element Q7 switches from the on state to the off state, and the collector-emitter of the switching element Q7 becomes non-conductive. The voltage at point D shown in FIG. 1 becomes the level of the DC power supply Vcc. As a result, the forward current IF of LED1 becomes 0 and LED1 is turned off.

(Modification 1) FIG. 5 is a diagram showing a structure of Modification 1 of the LED drive circuit 11 according to the first embodiment of the present invention. The feature of this modification is that the current mirror circuit 1
6, the resistors R11 and R12 are connected to the emitters of the PNP type transistors Q1 and Q2 that form the first and second transistors Q1 and Q2 of the current mirror circuit 15 shown in FIG.
Are connected in series to form the bandgap circuit 18 as the third and fourth transistors Q of the bandgap circuit 17.
The resistors R13 and R14 are connected in series to the emitters of the NPN transistors Q3 to Q4 that form the transistors Q3 and Q4. Note that the structure in which a resistor is connected to the emitter of the transistor shown in FIG. 5 can be applied to the transistors shown in FIGS.

Thus, by connecting the resistors in series to the emitters of the transistors Q1 to Q4, it is possible to suppress the Early effect which occurs in the transistors due to the voltage fluctuation of the DC power supply Vcc, and the currents I1 and I2. You can also adjust the current balance as a ratio of
It is possible to configure a constant current circuit that is not easily affected by the voltage fluctuation of the DC power supply Vcc.

(Modification 2) FIG. 6 is a diagram showing a structure of a modification 2 of the LED drive circuit 11 according to the first embodiment of the present invention. The feature of this modification is that the current mirror circuit 1
9, the PNP-MOSFET is used in place of the PNP type transistors forming the first and second transistors Q1 and Q2 of the current mirror circuit 15 shown in FIG. 1, and the response speed can be improved.

The effect of the present embodiment is that when the operation of the constant current circuit 14 is ON-controlled by the switching element Q7 in response to a pulse signal from the outside, the activation resistor R2 activates the current mirror circuit 19 to generate a current. Generate,
The bandgap circuit 17 receives the current generated from the current mirror circuit 19 to generate a constant current having a positive temperature coefficient and supplies it to the LED1 connected in series with the switching element Q7 and the constant current circuit 14. Conventional L
Compared with the ED drive circuits 101 and 102, the brightness of the LED 1 is stable, and the power supply efficiency can be improved.

In this embodiment, the switching element Q7 is provided and the operation of the constant current circuit 14 is controlled to be turned on by the switching element Q7 according to the pulse signal from the outside. Is not limited to such a case, and the switching element Q7 may be deleted from the configuration. That is, when a DC power source is applied to the LED 1 and the constant current circuit 14 connected in series, the current generated by the current mirror circuit 19 is banded by activating the current mirror circuit 19 by the activation resistor R2. Since the gap circuit 17 receives and generates a constant current having a positive temperature coefficient and supplies the constant current to the LED 1 connected in series to the constant current circuit 14, the conventional LE described above is used.
Compared with the D drive circuits 101 and 102, the brightness of the LED 1 is stable, and the power supply efficiency can be improved.

(Second Embodiment) FIG. 7 is a diagram showing a configuration of an LED drive circuit 21 according to a second embodiment of the present invention. As shown in FIG. 7, the LED drive circuit 21 is
The constant current circuit 23 that supplies a constant current having a negative temperature coefficient to the LED 1 and the LED 1 and the constant current circuit 23 that are connected in series are connected in series to the constant current circuit 23 according to a pulse signal from the outside. It is composed of a switching element Q7 for controlling the operation on / off.

Specifically, the constant current circuit 23 includes the current mirror circuit 15 as a current source and the current mirror circuit 1.
5 is composed of a starting resistor R2 for starting 5 and a reference voltage circuit 27 for receiving a current generated from the current mirror circuit 15 to generate a reference voltage and a constant current having a negative temperature coefficient. . Since the current mirror circuit 15 has been described in the first embodiment, its description is omitted.

In the constant current circuit 23 described above, the current mirror circuit 15 includes the PNP first transistor Q.
1 and a second transistor Q2, the emitters are commonly connected, the bases are commonly connected, and the base-collector of the second transistor Q2 is connected. The reference voltage circuit 27 includes an NPN-type third transistor Q3.
And a fourth transistor Q4, the bases of which are commonly connected, the collector of the first transistor Q1 and the collector and base of the third transistor Q3 are connected, and the collector of the second transistor Q2 and the fourth transistor Q4. Is connected to the collector of the third transistor Q3, and the emitter of the third transistor Q3 is at least one diode D1 to Dm.
Is connected to one end of the first resistor R1, and the emitter of the fourth transistor Q4 is connected to the other end of the first resistor R1. Furthermore, the starting resistor R2 is connected between the base of the second transistor Q2 and one end of the first resistor R1.

Next, the operation of the LED drive circuit 21 according to the present embodiment of the present invention will be described with reference to FIGS. The time t is the timing shown in FIG. Now, at time t0, the DC power supply Vcc is applied to the LED drive circuit 21, and the description starts with the base voltage of the switching element Q7 in the low level state. At this time, since the switching element Q7 is in the off state, the LED 1 and the constant current circuit 23
There is no current flowing through. That is, the forward current IF =
It is 0.

Next, at time t1, when the base voltage of the switching element Q7 switches from the low level to the high level, the switching element Q7 switches from the off state to the on state, and the collector-emitter of the switching element Q7 becomes conductive. The voltage at point D shown in FIG. 7 is almost GND.
Become a level. When the voltage at the point D shown in FIG. 7 becomes almost the GND level, first, the DC power supply Vcc passes through the anode and the cathode of the LED1, the emitter of the second transistor Q2 to the base, the starting resistor R2, and the collector of the switching element Q7 to the emitter. As a result, a starting current flows and it becomes easier to start. The base voltage at the point C shown in FIG. 7 drops according to this starting current, and the first and second transistors Q
1, Q2 turns on.

The minimum DC power supply Vcc that turns on only the first and second transistors Q1 and Q2 of the transistors Q1 to Q4 provided in the constant current circuit 23.
Assuming that the voltage of Vcc1 is Vcc1 as shown in FIG. 8, the above formula (1) is obtained.

Further, the first and second transistors Q
When 1 and Q2 are turned on, current flows from the base of the fourth transistor Q4 toward the emitter, and the fourth transistor Q4 is turned on. As a result, DC power supply Vcc to LED1
A current I2 flows through the anode and cathode of the second transistor Q2, the emitter and collector of the second transistor Q2, the collector and emitter of the fourth transistor Q4, and the collector and emitter of the switching element Q7.

At the same time, a current flows from the DC power supply Vcc to the anode and cathode of LED1, the emitter to collector of the first transistor Q1, the collector to emitter of the third transistor Q3, the diodes D1 to Dm, and the collector to emitter of the switching element Q7. I1 flows.

All the transistors Q1 to Q4 provided in the constant current circuit 23 are turned on to turn on the IF of the LED1.
The minimum voltage of the DC power supply Vcc that keeps constant is shown in FIG.
As shown in, if Vcc2,

[Equation 8]   Vcc2 = VF (LED1) + VCE (Q1) + VF (Q3)           + M × VF (D1 to Dm) + VCE (satQ7) (8) Becomes

As described above, the first and second transistors Q1 and Q2 form the current mirror circuit 15, and the current mirror circuit 15 is monolithically formed as a semiconductor integrated circuit. Formed by the first and second transistors Q1, Q
The currents I1 and I2 flowing through 2 are equal.

[0073]

[Equation 9]   I1 = I2 (9) Therefore, the forward current IF flowing in the LED 1 is

[Equation 10]   IF = I1 + I2 (10) Becomes

Since the voltage drop due to the first resistor R1 connected to the emitter of the fourth transistor Q4 is the same as the voltage drop due to the diodes D1 to Dm connected to the emitter of the third transistor Q3,

I2 = (m × VF) / R1 (11) The first resistor R1 is easier to set as the number of the diodes Dm increases. However, the starting resistance R
Since the starting voltage generated at 2 becomes high, the DC power supply Vcc also becomes high.

Furthermore, the first and second transistors Q
Since 1 and Q2 are formed in the same cell, I1 = I2
Next to

(12) I1 = I2 = 0.5 × IF (12) Further, by solving the equation (11), the currents I1, I2,
The forward current IF of LED1 can be obtained respectively.

The diode D in the reference voltage circuit 27
1 to Dm are junction temperatures T as shown in FIG.
It has a negative temperature coefficient with which the forward current IF decreases with respect to j.

Thus, at time t1, when the base voltage of the switching element Q7 switches from the low level to the high level, the switching element Q7 switches from the off state to the on state, and the collector-emitter of the switching element Q7 becomes conductive. The voltage at point D shown in FIG. 7 is almost at the GND level. As a result, the above-mentioned constant current forward current IF is generated in the LED 1, so that the LED 1 is turned on.

Next, at time t2, when the base voltage of the switching element Q7 switches from the high level to the low level, the switching element Q7 switches from the on state to the off state, and the collector-emitter of the switching element Q7 becomes non-conductive. The voltage at point D shown in FIG. 7 becomes the level of the DC power supply Vcc. As a result, the forward current IF of LED1 becomes 0 and LED1 is turned off. Since the first and second transistors Q1 and Q2 are formed in the same cell, I1 = I2 as in the above equation (13).
I was treated as

[Equation 13] The emitter area of Q1 <the emitter area of Q2 (13) may be used, and in this case, I1 <I2 may be treated from the area ratio of the transistors Q1 and Q2. When the constant current circuit 23 is monolithically formed as a semiconductor integrated circuit, the resistance value of the first resistor R1 has a positive temperature coefficient.

The effect of the present embodiment is that when the operation of the constant current circuit 23 is controlled to be turned on by the switching element Q7 in response to a pulse signal from the outside, the activation resistor R2 activates the current mirror circuit 15 to generate a current. Generate,
The current generated by the current mirror circuit 15 is received by the reference voltage circuit 27 to generate a reference voltage and a constant current having a negative temperature coefficient.
Compared with the drive circuits 101 and 102, the brightness of the LED is stable, and the power efficiency can be improved.

In the present embodiment, the switching element Q7 is provided and the operation of the constant current circuit 23 is controlled to be turned on by the switching element Q7 according to a pulse signal from the outside. Is not limited to such a case, and the switching element Q7 may be deleted from the configuration. That is, when a DC power source is applied to the LED 1 and the constant current circuit 23 connected in series, the starting resistor R2 starts the current mirror circuit 15 to generate a current, and the current generated from the current mirror circuit 15 is used as a reference. Since the voltage circuit 27 receives the voltage to generate the reference voltage and the constant current having a negative temperature coefficient, the brightness of the LED is more stable and the power efficiency is higher than that of the conventional LED driving circuits 101 and 102. It can contribute to improvement.

(Third Embodiment) FIG. 10 is a diagram showing a configuration of an LED drive circuit 31 according to a third embodiment of the present invention. As shown in FIG. 10, the LED drive circuit 31
Is a constant current circuit 33 that supplies a constant current having a temperature coefficient of a predetermined sign and magnitude to the LED 1, and is connected in series to the LED 1 and the constant current circuit 33 that are connected in series to generate a pulse signal from the outside. Accordingly, the switching element Q7 controls ON / OFF of the operation of the constant current circuit 33.

More specifically, the constant current circuit 33 includes the current mirror circuit 15 as a current source and the current mirror circuit 1.
5, a starting resistor R2 for starting 5, a reference voltage circuit 35 that receives a current generated from the current mirror circuit 15 to generate a reference voltage and a constant current having a negative temperature coefficient, and a reference voltage circuit 35. And a bandgap circuit 37 for receiving a constant current generated from the above and generating a constant current having a temperature coefficient of a predetermined sign and magnitude.

The first resistor R1 and the third resistor R1
3 limits the current flowing through the fourth transistor Q4 and the fifth transistor Q5 and adjusts the temperature coefficient of the current flowing through the sixth transistor Q6.

Next, the operation of the LED drive circuit 31 according to this embodiment of the present invention will be described with reference to FIGS. The time t is the timing shown in FIG. Now, at time t0, the DC power supply Vcc is applied to the LED drive circuit 31, and the description starts with the base voltage of the switching element Q7 being in the low level state. At this time, since the switching element Q7 is in the off state, no current flows in the LED 1 and the constant current circuit 33. That is, the forward current I
F = 0.

Next, at time t1, when the base voltage of the switching element Q7 switches from the low level to the high level, the switching element Q7 switches from the off state to the on state, and the collector-emitter of the switching element Q7 becomes conductive. The voltage at point D shown in FIG. 10 is almost GN.
It becomes D level.

When the voltage at the point D shown in FIG. 10 becomes almost GND level, first, from the DC power supply Vcc, the anode and cathode of the LED1, the emitter and base of the second transistor Q2, the starting resistor R2, and the collector and emitter of the switching element Q7. A startup current flows via and it becomes easy to start up. Since the starting resistor R2 has a resistance value on the order of MΩ, the starting current has a value on the order of μA.

In accordance with this starting current, the base voltage at point C shown in FIG. 10 drops, and the first and second transistors Q
1, Q2 turns on. Further, when the first and second transistors Q1 and Q2 are turned on, current flows from the bases of the third and fourth transistors Q3 and Q4 toward the emitters, and the third and fourth transistors Q3 and Q4 are turned on.

As a result, from the DC power supply Vcc, the anode and cathode of LED1, the emitter and collector of the second transistor Q2, the collector and emitter of the fourth transistor Q4, the first resistor R1, the collector and emitter of the fifth transistor Q5, and the third A current I2 flows from the resistor R3 and the collector of the switching element Q7 via the emitter.

At this time, since the fifth transistor Q5 is turned on, the sixth transistor Q6 is turned on at the same time, and the DC power supply Vcc turns on the anode and cathode of the LED1, the collector and emitter of the sixth transistor Q6, and the collector of the switching element Q7. A current I3 flows through the emitter.

Further, since the third transistor Q3 is turned on, the DC power supply Vcc causes the anode and cathode of the LED1, the emitter and collector of the first transistor Q1, the collector and emitter of the third transistor Q3, the diodes D1 to Dm, and the switching element Q7. A current I1 flows from the collector of the above through the emitter.

Here, the forward current IF flowing in the LED 1
Is the sum of the currents flowing through the reference voltage circuit 35 and the bandgap circuit 37,

[Equation 14]   IF = I1 + I2 + I3 (14) Becomes

As described above, the first and second transistors Q1 and Q2 form the current mirror circuit 15, and the current mirror circuit 15 is monolithically formed as a semiconductor integrated circuit. Formed by the first and second transistors Q1, Q
The currents I1 and I2 flowing through 2 are equal.

[0093]

[Equation 15]   I1 = I2 (15) Therefore, the forward current IF flowing in the LED 1 is

[Equation 16]   IF = 2 x I1 + I3       = 2 × (((m × VF (Dm))-VF (Q5)) / (R1 + R3)) + I3       = 2 * ((m-1) VF / (R1 + R3)) + I3 (16) Becomes

The voltage drop between A-C-D shown in FIG.
Since the voltage drop between A and D shown in FIG. 10 is the same,

[Equation 17] Becomes

Solving the above equations (16) and (17),
The resistance constant and the currents I1, I2, I3 can be set. When the semiconductor integrated circuit is monolithically formed, the third resistor R3 has a positive temperature coefficient, as shown in FIG. 11, and the current I flowing through the sixth transistor Q6.
The temperature coefficient of 3 is more positive than the currents I1 and I2.

Further, the diodes D1 to Dm in the reference voltage circuit 35 have a negative temperature coefficient with which the forward voltage VF decreases with respect to the junction temperature Tj, as shown in FIG.

Therefore, the temperature coefficient of the forward current IF flowing in the LED 1 can be freely adjusted by adjusting the current balance between the currents I1 and I2 and the current I3.

That is, the forward current IF having a temperature coefficient of a predetermined sign and magnitude can be supplied.

Further, since the sixth transistor Q6 is made into a multi-emitter so that a relatively large current can flow, the cell area of the first and second transistors Q1 and Q2 can be reduced, and a PNP transistor can be formed. It is possible to avoid a decrease in area efficiency due to use.
Therefore, the monolithic formation of the semiconductor integrated circuit can contribute to the reduction of the chip area.

Further, as shown in FIG. 10, in the constant current circuit 33 in the present embodiment, the reference voltage circuit 35 and the band gap circuit 37 are used in combination, so that the temperature characteristics of the constant current are made flat. It is possible to bring them closer together.

At the same time, the reference current is applied to the transistors Q1 to Q.
5, diodes D1 to Dm, first resistor R1, third resistor R
3, and the bandgap circuit 37 constitutes a current mirror circuit. Therefore, if the circuit constants are set so that most of the current flowing through the constant current circuit 33 flows through the sixth transistor Q6, the area of the element is reduced. And can be easily made into a monolithic IC,
It is possible to avoid a reduction in area efficiency due to the use of PNP type transistors.

The effect of this embodiment is that when the operation of the constant current circuit 33 is ON-controlled by the switching element Q7 in response to the pulse signal from the outside, the current is supplied by activating the current mirror circuit 15 by the activation resistor R2. Generate,
The reference voltage circuit 35 receives the current generated from the current mirror circuit 15 to generate a reference voltage, generates a constant current having a negative temperature coefficient, and further receives the constant current generated from the reference voltage circuit 35. Since the bandgap circuit 37 generates a constant current having a temperature coefficient of a predetermined sign and magnitude, the conventional LED drive circuit 10
Compared with 1,102, the brightness of the LED is more stable,
In addition, it can contribute to the improvement of power supply efficiency.

In the present embodiment, the switching element Q7 is provided and the operation of the constant current circuit 33 is controlled to be turned on by the switching element Q7 according to the pulse signal from the outside. Is not limited to such a case, and the switching element Q7 may be deleted from the configuration. That is, when a DC power source is applied to the LED 1 and the constant current circuit 33 connected in series, the starting resistor R2 starts the current mirror circuit 15 to generate a current, and the current generated from the current mirror circuit 15 is used as a reference. The voltage circuit 35 receives the constant voltage to generate a reference voltage and a constant current having a negative temperature coefficient. Further, the bandgap circuit 37 receives the constant current generated from the reference voltage circuit 35 and has a predetermined sign and magnitude. Since the constant current having the temperature coefficient of is generated, it is possible to further stabilize the brightness of the LED and contribute to the improvement of the power supply efficiency as compared with the conventional LED drive circuits 101 and 102.

(Application Example 1) FIG. 13 shows the LED drive circuits 11 and 2 according to the above-described first to third embodiments of the present invention.
It is a figure which shows the structure of the LED drive device 41 which applied 1,31. As shown in FIG. 13, the LED driving device 41 is
Switches SW1 to SW4, which are, for example, contacts of a relay or semiconductor switches, and switches SW1 to SW4, which turn on and off the connection lines supplied from the DC power supply Vcc to the respective LEDs 11 to 44 in accordance with control signals CNTY1 to 4 input from the outside. LEDs 11 to 44 that are respectively connected to L,
Constant current circuits ICC11 to 44 connected to the ED11 to 44 respectively to supply a constant current, and constant current circuits ICC11 to 44 according to pulse signals PX1 to 4 input from the outside.
Switching element Q that controls the on / off operation of each
71 to 74 are respectively connected in series.

The LED driving device 41 is provided with a switch SW1 according to control signals CNTY1 to CNTY4 input from the outside.
~ 4 is controlled to be turned on and off, the LED to be lit is specified,
Furthermore, since the lighting timing of the LEDs is specified according to the pulse signals PX1 to 4 input from the outside, by setting the generation timing of the pulse signals PX1 to 4 to a frequency above which flicker does not matter, a display device is obtained. Available.

The constant current circuits ICC11 to 44 used in the LED drive device 41 can be used in any of the LED drive circuits 11 to 31 shown in the first to third embodiments. The breakdown voltage of the transistor is, for example, about 7-8V
In this case, even if a reverse bias voltage is generated during dynamic lighting, the LED is not destroyed and the voltage of the DC power supply Vcc can be increased. Further, since the constant current circuit has a high impedance characteristic, the current value IF becomes constant even if the voltage of the DC power supply Vcc increases.

Dynamically driven L as shown in FIG.
Assuming a case where a large number of LEDs having the same luminous intensity are mounted on the ED drive device 41, (1) no matter which of the constant current circuits shown in the first to third embodiments is used, the LEDs are DC Since a stable constant current forward current IF can be supplied irrespective of the voltage of the power source Vcc or the forward voltage VF, it is extremely unlikely that the light intensity varies among the LEDs. Further, when the switching elements Q71 to Q74 for controlling the ON / OFF of the LED are in the off state, the constant current circuit is also in the off state, so that no unnecessary current other than the current generated at the time of lighting does not flow, resulting in high efficiency. A "constant current LED driver" can be realized.

(2) A monolithic IC having high area efficiency can be realized by, for example, ICCs 11 to 44 and Q71 to 74, and an LED defect detection function and a surge protection function can be added.

(3) Even with lighting by dynamic drive,
Since the constant current circuit has a high withstand voltage value, current does not sneak into other LEDs that are not directly driven by the constant current circuit,
LED lighting failure is unlikely to occur. In other words, the voltage of the DC power supply Vcc can be increased. L in the conventional constant current circuit
Since the voltage of the DC power supply Vcc is determined by the withstand voltage value of the ED, a low power supply voltage of, for example, about 5V is assumed.

(Application Example 2) FIG. 14 is a circuit diagram of the LED drive circuits 11 and 12 according to the above-described first to third embodiments of the present invention.
It is a figure which shows the structure of the LED drive device 51 which applied 1,31. As shown in FIG. 14, the LED driving device 51 is
In accordance with control signals CNTY1 to 4 input from the outside, the constant current circuits ICC51 to 54 from the DC power supply Vcc.
Switches SW1 to SW4 each of which includes a contact of a relay or a semiconductor switch for turning on / off a connection line supplied to
According to the constant current circuits ICC51 to 54 respectively connected to the switches SW1 to SW4, the LEDs 11 to 44 emitting light by the current supplied from the constant current circuits ICC51 to 54, and the pulse signals PX1 to 4 input from the outside. LED
Switching elements Q71 to 74, which respectively control the operations of 11 to 44 on and off, are connected in series.

This LED driving device 51 has a switch SW1 according to control signals CNTY1 to CNTY4 input from the outside.
~ 4 is controlled to be turned on and off, the LED to be lit is specified,
Furthermore, since the lighting timing of the LEDs is specified according to the pulse signals PX1 to 4 input from the outside, by setting the generation timing of the pulse signals PX1 to 4 to a frequency above which flicker does not matter, a display device is obtained. Available. Since the LED drive device 51 shown in the application example 2 is characterized by the same features as in the application example 1 described above, the description thereof will be omitted.

(Fourth Embodiment) FIG. 19 is a diagram showing the structure of an LED drive circuit 201 according to a fourth embodiment of the present invention. As shown in FIG. 19, the LED drive circuit 20
Reference numeral 1 denotes an ON-OFF control circuit 211 that generates an activation trigger and a stop signal that are alternately repeated according to a pulse signal from the outside to control ON / OFF of the operation of the constant current circuit 213;
A start trigger and a stop signal are input from the N-OFF control circuit 211, and the light emitting diode LED is received according to the start trigger.
1 while supplying a constant current to the LED1 in response to the stop signal
And a constant current circuit 213 for stopping the constant current supplied to the.

More specifically, the ON-OFF control circuit 211
Has three NPN type transistors, that is, a fifth transistor Q5, a sixth transistor Q6 and a seventh transistor Q7. The seventh transistor Q7 is
A pulse signal from the outside is input to the base, the control system power supply Vcc of the control circuit system is connected to the collector via the resistor R3, and the emitter is connected to GND via the resistor R4. Further, the collector of the seventh transistor Q7 and the resistor R
3 is connected to diode D via capacitor C1
0, and the cathode of the diode D0 is connected to the base of the fifth transistor Q5. On the other hand, the emitter of the seventh transistor Q7 and the resistor R4
The connection point between and is connected to the base of the sixth transistor Q6. Further, one end of the starting resistor R2 is connected to the constant current circuit 2
First and second transistors Q1 and Q provided in
The emitter of 2 and the cathode of LED1 are commonly connected A
The other end of the starting resistor R2 is connected to the collector of the fifth transistor Q5. Further, at a point B where the emitter of the fifth transistor Q5 and the collector of the sixth transistor Q6 are commonly connected, the collector of the first transistor Q1 and the collector and base of the third transistor Q3 are commonly connected.

The constant current circuit 213 is a light emitting diode LE.
A current mirror circuit 215 for supplying a constant current to D1,
The band gap circuit 217 is configured to receive a current generated from the current mirror circuit 215 and generate a constant current having a positive temperature coefficient. Further, it has the temperature characteristic of constant current as in the first embodiment. In particular, the bandgap circuit 217 includes the ON-OFF control circuit 21.
A start trigger and a stop signal are input from 1 to start the supply of a constant current to the current mirror circuit 215 according to the start trigger, while the current mirror circuit 2 receives a stop signal.
15 is responsible for stopping the supply of constant current.

In the constant current circuit 213, the current mirror circuit 215 has a PNP type first transistor Q1 and a second transistor Q2, the emitters of which are commonly connected, the bases of which are commonly connected, and the second transistor Q2.
Two base-collectors are connected. The bandgap circuit 217 includes an NPN-type third transistor Q.
The third and fourth transistors Q4 have their bases connected in common, the collector of the first transistor Q1 is connected to the collector and base of the third transistor Q3, and the collector of the second transistor Q2 is connected to the collector of the fourth transistor Q4. And the emitter of the third transistor Q3 is connected to one end of the first resistor R1.
The four emitters are connected to the other end of the first resistor R1. The first resistor R1 is provided to limit the current flowing through the fourth transistor Q4.

Next, the operation of the LED drive circuit 201 according to the present embodiment of the present invention will be described with reference to FIGS. The time t is the timing shown in FIGS. 20 and 21. Now, at time t10, the control system power supply Vcc is applied to the LED drive circuit 201, and the description starts with the base voltage of the seventh transistor Q7 being in the high level state. At this time,
The seventh transistor Q7 is in the ON state, but LE
No current flows through D1 and the constant current circuit 213.
That is, the forward current IF = 0. Further, since the collector current is flowing in the collector of the seventh transistor Q7, no charge is stored in the capacitor C1.

(1) Lighting Operation Next, at time t11, when the base voltage of the seventh transistor Q7 switches from high level to low level,
The seventh transistor Q7 switches from the on state to the off state, the collector of the seventh transistor Q7 shifts to the open state, and the charging current flows from the control system power supply Vcc to the capacitor C1 via the resistor R3.

At this time, since a high level pulse signal is input as a start trigger from the capacitor C1 to the base of the fifth transistor Q5 via the diode D0, the fifth transistor Q5 is turned on only during the high level period of the start trigger. An activation trigger appears at point B.

As a result, the drive system power source VLED to LED
1. From the collector to the emitter of the fifth transistor Q5 via the starting resistor R2, further increase the base voltage of the third transistor Q3 to turn on the third transistor Q3, and the current IR2 from the base to the emitter of the third transistor Q3. Flows. Since the starting resistor R2 has a resistance value on the order of hundreds of Ω, the starting current has a value on the order of 10 mA. Since the voltage at the point B shown in FIG. 19 rises according to this starting current, the third and fourth transistors Q3, Q
4 turns on. Furthermore, the third and fourth transistors Q
When Q3 and Q4 are turned on, the first and second transistors Q
Current flows from the emitter of 1, Q2 to the base,
The first and second transistors Q1 and Q2 are turned on.

As a result, the drive system power source VLED to LED1
A current I1 flows from the anode and cathode of the first transistor Q1, the emitter of the first transistor Q1 to the collector, and the collector of the third transistor Q3 to the emitter. At the same time, current I2 flows from the drive system power supply Vcc through the anode and cathode of LED1, the emitter and collector of the second transistor Q2, and the collector and emitter of the fourth transistor Q4. As described above, the first and second transistors Q
1 and Q2 constitute a current mirror circuit 215. Further, since the current mirror circuit 215 is monolithically formed as a semiconductor integrated circuit, the first and second transistors Q1 and Q1 formed in the same cell.
The currents I1 and I2 flowing through 2 are equal.

[0121]

[Equation 18]   I1 = I2 (18) Therefore, the forward current IF flowing in the LED 1 is

[Formula 19]   IF = I1 + I2 (19) Becomes

That is, since the multi-emitter is adopted as the emitter of the fourth transistor Q4, the first resistor R1
By adjusting the above, I1 = I2 is established, and since the first and second transistors Q1 and Q2 are formed in the same cell,

[Equation 20]   I1 = I2 = 0.5 × IF (20) Becomes

Since the emitter area S (Q4) of each fourth transistor Q4 and the emitter area S (Q3) of the third transistor Q3 are formed in the same cell, the fourth transistor Q4 is used. Let n be the number of cells in

[Equation 21]   S (Q4) = n · S (Q3) (21) Becomes

Here, the base of the third transistor Q3
Voltage drop between emitters VBE (Q3) = VBE (Q4) + I
Since the relationship of 2 × R1 is established, the above equation (7)
Becomes Solving the above equation (7), the currents I1, I2,
The forward current IF of LED1 can be obtained respectively. The forward current IF generated by the bandgap circuit 217 increases as the junction temperature Tj rises, as shown in FIG.

As described above, at time t11, when the base voltage of the seventh transistor Q7 switches from the high level to the low level, the transistor Q7 switches from the on state to the off state, the collector of the transistor Q7 enters the open state, and the capacitor Q7 opens. A start trigger is generated from C1 and a start current IR2 flows through the fifth transistor Q5,
The bandgap circuit 217 is activated. As a result, LE
Since the above-mentioned constant current forward current IF is generated in D1,
LED1 lights up.

Next, the reset pulse signal will be described with reference to FIG. First, it is assumed that the control system power supply Vcc has already risen. At time t20, supply of the drive system power supply VLED is started, and it is assumed that the drive system power supply VLED is stable between the times t21 and t24.

Here, from time t22 to t23, E
If the reset pulse signal is applied to the point once from the outside, the LE pulse signal is applied after the falling edge (t23) of the reset pulse signal.
IF flows to D1. In FIG. 21, from time t24.
At t27, there is a voltage fluctuation in the drive system power supply VLED,
According to the present embodiment, since the constant current circuit 213 is used, the influence due to the voltage fluctuation does not appear in IF and is stable.

(2) Extinguishing Operation Next, at time t12, when the base voltage of the seventh transistor Q7 switches from low level to high level,
The seventh transistor Q7 is switched from the off state to the on state, and the collector-emitter of the seventh transistor Q7 becomes conductive. As a result, the base voltage of the sixth transistor Q6 switches from the low level to the high level, the collector-emitter of the sixth transistor Q6 becomes conductive, and the GND level stop signal is generated at the point B. A current I1 flows from VLED through the anode and cathode of LED1, the emitter and collector of the first transistor Q1, and the collector and emitter of the sixth transistor Q6.

In response to this stop signal, the voltage at the point B shown in FIG. 19 becomes the GND level, and at the same time, the third and fourth transistors Q3 and Q4 are turned off, and accordingly the current mirror circuit 215 is turned off. Second transistor Q
Since the supply of the current I2 flowing in 2 is stopped and becomes 0, the current I1 flowing in the first transistor Q1 also becomes 0. As a result, the forward current IF of LED1 becomes 0 and LED1 is turned off.

Immediately after the base voltage of the sixth transistor Q6 is switched from the low level to the high level, the parasitic capacitance of the semiconductor integrated circuit is maintained during the ON period of the collector current Ic flowing between the collector and the emitter of the sixth transistor Q6. It is decided by.

(Modification 1) FIG. 22 is a diagram showing a structure of modification 1 of the LED drive circuit 221 according to the first embodiment of the present invention. The current mirror circuit 21 shown in FIG.
In 5, the starting resistor R2 was connected to point A,
In this modification, in the ON-OFF control circuit 231,
One end of the starting resistor R2 is directly connected to the control system power supply Vcc, while the other end of the starting resistor R2 is connected to the fifth transistor Q5.
To connect to the collector.

As shown in FIG. 22, the starting resistor R2 is connected to the control system power supply Vcc from the collector of the fifth transistor Q5.
The configuration of directly connecting to the
It is also applicable to the configuration shown in FIG. Thus, the fifth
By directly connecting the starting resistor R2 from the collector of the transistor Q5 to the control system power supply Vcc, an ON-OFF control circuit 231 serving as a control system is connected to the control system power supply Vcc, and independently of this, the drive system power supply VLED. A constant current circuit 233, which serves as a drive system, and the LED 1 can be connected in series.
As a result, it is possible to configure the ON-OFF control circuit 231 that is less likely to be affected by the voltage fluctuation of the drive system power supply VLED.

(Fifth Embodiment) FIG. 23 is a diagram showing the structure of an LED drive circuit 241 according to a fifth embodiment of the present invention. The fifth embodiment has almost the same basic configuration as the LED drive circuit 201 corresponding to the fourth embodiment shown in FIG. 19, and the same components are designated by the same reference numerals. , Its description will be omitted.

As shown in FIG. 23, the LED drive circuit 24
The first feature is that the constant current circuit 251 is provided. Further, it has a temperature characteristic of constant current as in the second embodiment. The constant current circuit 251 is the ON-OFF control circuit 2
11. A function of inputting a start trigger and a stop signal from 11 to start the supply of constant current to the current mirror circuit 215 in response to the start trigger, and stopping the supply of constant current to the current mirror circuit 215 in response to the stop signal. I am in charge. Further, the reference voltage circuit 257 receives the current generated from the current mirror circuit 215, generates a reference voltage, and also generates a constant current having a negative temperature coefficient.

The reference voltage circuit 257 has an NPN-type third transistor Q3 and a fourth transistor Q4, the bases of which are commonly connected, and the collector of the first transistor Q1 and the collector and the base of the third transistor Q3 are connected. The collector of the second transistor Q2 and the collector of the fourth transistor Q4 are connected to each other, and the third transistor Q3
The emitters of at least one diode D1-D
It is connected to one end of the first resistor R1 via m, and the emitter of the fourth transistor Q4 is connected to the other end of the first resistor R1.

Next, the operation of the LED drive circuit 241 according to this embodiment of the present invention will be described with reference to FIGS. The time t is each timing shown in FIG. (1) Lighting Operation Next, at time t11, the ON-OFF control circuit 21
In No. 1, when the base voltage of the seventh transistor Q7 switches from high level to low level, the seventh transistor Q7
7 switches from the ON state to the OFF state, the collector of the seventh transistor Q7 shifts to the open state, and the charging current flows from the control system power supply Vcc to the capacitor C1 via the resistor R3.

At this time, since a high level pulse signal is input as a start trigger from the capacitor C1 to the base of the fifth transistor Q5 via the diode D0, the fifth transistor Q5 is turned on only during the high level period of the start trigger. An activation trigger appears at point B. As a result, the drive system power source VLED passes through the LED1 and the starting resistor R2 from the collector to the emitter of the fifth transistor Q5, and further the base voltage of the third transistor Q3 is increased to turn on the third transistor Q3 and turn on the third transistor Q3. A current IR2 flows from the base of Q3 to the emitter and further through the diodes D1 to Dm.

Since the voltage at the point B shown in FIG. 23 rises according to this starting current, the third and fourth transistors Q are generated.
3, Q4 turns on. Further, when the third and fourth transistors Q3 and Q4 are turned on, current flows from the emitters of the first and second transistors Q1 and Q2 toward the bases, and the first and second transistors Q1 and Q2 are turned on.

As a result, the drive system power source VLED to LED1
Current I1 flows through the anode and cathode of the first transistor Q1, the emitter of the first transistor Q1 to the collector, the collector of the third transistor Q3 to the emitter, and the diodes D1 to Dm. At the same time, a current I2 flows from the drive system power supply VLED through the anode and cathode of LED1, the emitter and collector of the second transistor Q2, and the collector and emitter of the fourth transistor Q4.

Thus, at time t11, when the base voltage of the seventh transistor Q7 switches from the high level to the low level, the transistor Q7 switches from the on state to the off state, the collector of the transistor Q7 goes into the open state, and the capacitor A start trigger is generated from C1 and a start current IR2 flows through the fifth transistor Q5,
The reference voltage circuit 257 is activated. As a result, the above-mentioned constant current forward current IF is generated in the LED 1,
1 lights up.

(2) Extinguishing Operation Next, at time t12, when the base voltage of the seventh transistor Q7 switches from low level to high level,
The seventh transistor Q7 is switched from the off state to the on state, and the collector-emitter of the seventh transistor Q7 becomes conductive. As a result, the base voltage of the sixth transistor Q6 switches from the low level to the high level, the collector-emitter of the sixth transistor Q6 becomes conductive, and the GND level stop signal is generated at the point B. A current I1 flows from VLED through the anode and cathode of LED1, the emitter and collector of the first transistor Q1, and the collector and emitter of the sixth transistor Q6.

In response to this stop signal, the voltage at point B shown in FIG. 23 becomes the GND level, and at the same time, the third and fourth transistors Q3 and Q4 are turned off, and accordingly the current mirror circuit 215 is turned off. Second transistor Q
Since the supply of the current I2 flowing in 2 is stopped and becomes 0, the current I1 flowing in the first transistor Q1 also becomes 0. As a result, the forward current IF of LED1 becomes 0 and LED1 is turned off.

(Sixth Embodiment) FIG. 24 is a diagram showing the structure of an LED drive circuit 261 according to a sixth embodiment of the present invention. The sixth embodiment has almost the same basic configuration as the LED drive circuit 241 corresponding to the fifth embodiment shown in FIG. 23, and the same components are designated by the same reference numerals. , Its description will be omitted.

As shown in FIG. 24, the LED drive circuit 26
The first feature is that the reference voltage circuit 275 provided in the constant current circuit 273 has a bandgap circuit 277. In the constant current circuit 273 of this embodiment, the reference voltage circuit 275 and the bandgap circuit 277 are used in combination, so that the temperature characteristic of the constant current can be made flat as in the third embodiment. have.

The bandgap circuit 277 has an NPN type eighth transistor Q8 and a ninth transistor Q9, the bases of which are commonly connected to the resistor R1 which is connected to the collector of the fourth transistor Q4. The collector and base of the transistor Q8 are connected, the emitter of the second transistor Q2 and the collector of the ninth transistor Q9 are connected, the emitter of the eighth transistor Q8 is connected to one end of the resistor R5, and the emitter of the ninth transistor Q9 is GND. And is also connected to the other end of the resistor R5. The resistor R5 is the eighth transistor Q8.
It is provided to limit the current flowing to the.

Next, the operation of the LED drive circuit 261 according to this embodiment of the present invention will be described with reference to FIGS. The time t is each timing shown in FIG. (1) Lighting Operation Next, at time t11, the ON-OFF control circuit 21
In No. 1, when the base voltage of the seventh transistor Q7 switches from high level to low level, the seventh transistor Q7
7 switches from the ON state to the OFF state, the collector of the seventh transistor Q7 shifts to the open state, and the charging current flows from the control system power supply Vcc to the capacitor C1 via the resistor R3.

At this time, since a high level pulse signal is input as a start trigger from the capacitor C1 to the base of the fifth transistor Q5 via the diode D0, the fifth transistor Q5 is turned on only during the high level period of the start trigger. An activation trigger appears at point B.

As a result, the drive system power source VLED to LED
1. From the collector of the fifth transistor Q5 to the emitter through the starting resistor R2, further increase the base voltage of the third transistor Q3 to turn on the third transistor Q3, and further from the base to the emitter of the third transistor Q3. A current IR2 flows through the diodes D1 to Dm.

Since the voltage at the point B shown in FIG. 24 rises according to this starting current, the third and fourth transistors Q
3, Q4 turns on. Further, when the third and fourth transistors Q3 and Q4 are turned on, current flows from the emitters of the first and second transistors Q1 and Q2 toward the bases, and the first and second transistors Q1 and Q2 are turned on.

As a result, the drive system power source VLED to LED1
Of the second transistor Q2 from the emitter to the collector, the fourth transistor Q4 from the collector to the emitter, the first resistor R1, the eighth transistor Q8 from the collector to the emitter, and the resistor R5 to the current I
2 flows.

At this time, since the eighth transistor Q8 is turned on, at the same time, the ninth transistor Q9 is turned on, and the drive system power source VLED changes the anode, cathode and
G from the collector of the transistor Q9 via the emitter
A current I3 flows to ND.

Further, since the third transistor Q3 is turned on, the drive system power supply VLED to the anode and cathode of LED1, the emitter to collector of the first transistor Q1,
A current I1 flows from the collector of the third transistor Q3 to the emitter via the diodes D1 to Dm to GND.

Here, the forward current IF flowing in the LED 1
Is the sum of the currents flowing through the reference voltage circuit 275 and the bandgap circuit 277.

[Equation 22]   IF = I1 + I2 + I3 (22) Becomes

As described above, the first and second transistors Q1 and Q2 form the current mirror circuit 215. Further, since the current mirror circuit 215 is monolithically formed as a semiconductor integrated circuit, it is formed in the same cell. Formed by the first and second transistors Q
The currents I1 and I2 flowing through 1 and Q2 are equal.

Therefore, the forward current IF flowing in the LED 1 is
Is

IF = 2 × I1 + I3 (23) (2) Light-off operation Next, at time t12, when the base voltage of the seventh transistor Q7 switches from low level to high level,
The seventh transistor Q7 is switched from the off state to the on state, and the collector-emitter of the seventh transistor Q7 becomes conductive. As a result, the base voltage of the sixth transistor Q6 switches from the low level to the high level, the collector-emitter of the sixth transistor Q6 becomes conductive, and the GND level stop signal is generated at the point B. A current I1 flows from VLED through the anode and cathode of LED1, the emitter and collector of the first transistor Q1, and the collector and emitter of the sixth transistor Q6.

In response to this stop signal, the voltage at point B shown in FIG. 24 becomes GND level, and at the same time, the third and fourth transistors Q3 and Q4 are turned off, and accordingly the current mirror circuit 215 is turned off. Second transistor Q
Since the supply of the current I2 flowing in 2 is stopped and becomes 0, the current I1 flowing in the first transistor Q1 also becomes 0.

At the same time, in response to the turning off of the fourth transistor Q4, the eighth band gap circuit 277 is turned on.
Since the supply of the current I2 flowing in the transistor Q8 is stopped and becomes 0, accordingly, the ninth transistor Q9
The current I3 that was flowing into the memory also becomes zero. As a result, LED1
Forward current IF becomes 0 and the LED 1 is turned off.

(Seventh Embodiment) FIG. 25 is a diagram showing the structure of an LED drive circuit 281 according to the seventh embodiment of the present invention. As shown in FIG. 25, the LED drive circuit 2
Reference numeral 81 designates an ON-OFF control circuit 291 for ON / OFF controlling the operation of the constant current circuit 293 by generating a lighting signal and a stop signal which are alternately repeated in response to a pulse signal from the outside.
A constant current for inputting a lighting signal and a stop signal from the N-OFF control circuit 291 and supplying a constant current to the light emitting diode LED1 according to the lighting signal, while stopping the constant current supplied to the LED1 according to the stop signal. And a circuit 293. Note that the current mirror circuit 215 and the bandgap circuit 217 that form the constant current circuit 293 have been described above, and therefore description thereof will be omitted.

More specifically, the ON-OFF control circuit 291
Has a seventh NPN transistor Q7. A pulse signal from the outside is input to the base of the seventh transistor Q7, and one end of the starting resistor R2 has a constant current circuit 293.
The emitters of the first and second transistors Q1 and Q2 and the cathode of the LED1 are connected in common to the point A, while the other end of the starting resistor R2 is connected to the collector of the seventh transistor Q7. Has been done. further,
To the point B to which the collector of the seventh transistor Q7 is connected, the collector of the first transistor Q1 and the collector and base of the third transistor Q3 are commonly connected.

Next, the operation of the LED drive circuit 281 according to this embodiment of the present invention will be described with reference to FIG. Note that the time t is each timing shown in FIG. Now, at time t30, the drive system power supply VLED is applied to the LED drive circuit 281, and the description will start assuming that the base voltage of the seventh transistor Q7 is in the low level state. At this time, the seventh transistor Q
Since 7 is in the off state, current is flowing through the LED 1 and the constant current circuit 293. That is, the forward current IF = I1 + I2.

(1) At turn-off operation time t31, when the base voltage of the seventh transistor Q7 switches from low level to high level, the seventh transistor Q7 switches from off state to on state,
The collector and the emitter of the seventh transistor Q7 become conductive.

As a result, a GND level stop signal is generated at the point B at the collector of the seventh transistor Q7, so that the drive system power source VLED causes the anode and cathode of LED1 and the emitter and collector of the first transistor Q1 reach
A current I1 flows from the collector of the seventh transistor Q7 via the emitter.

Since the voltage at the point B shown in FIG. 25 becomes the GND level, at the same time, the third and fourth transistors Q3 and Q3 are connected.
Q4 is turned off, and in response to this, the current I2 flowing through the second transistor Q2 of the current mirror circuit 215.
Is stopped and becomes 0, the first transistor Q
The current I1 flowing in 1 also becomes 0. As a result, the LED
The forward current of 1 becomes IF = 0, and the LED 1 is turned off.
When the light is turned off, the current IR2 flowing through the starting resistor R2 is as small as several μA and the LED1 is not turned on.

Immediately after the base voltage of the seventh transistor Q7 is switched from low level to high level, the parasitic capacitance of the semiconductor integrated circuit is maintained during the ON period of the collector current Ic flowing between the collector and the emitter of the seventh transistor Q7. It is decided by.

(2) Lighting Operation Next, at time t32, when the base voltage of the seventh transistor Q7 switches from the high level to the low level,
The seventh transistor Q7 switches from the ON state to the OFF state, the collector of the seventh transistor Q7 shifts to the open state, and the drive system power source VLED to LED1 and the starting resistor R
The collector of the seventh transistor Q7 becomes high level via 2 and a lighting signal appears at the point B. The starting resistance R
Since 2 has a resistance value on the order of several MΩ, the starting current has a value on the order of μA.

Since the voltage at the point B shown in FIG. 25 rises according to this starting current, the third and fourth transistors Q
3, Q4 turns on. Further, when the third and fourth transistors Q3 and Q4 are turned on, current flows from the emitters of the first and second transistors Q1 and Q2 toward the bases, and the first and second transistors Q1 and Q2 are turned on.

As a result, the drive system power source VLED to LED1
A current I1 flows from the anode and cathode of the first transistor Q1, the emitter of the first transistor Q1 to the collector, and the collector of the third transistor Q3 to the emitter. At the same time, a current I2 flows from the drive system power source VLED through the anode and cathode of LED1, the emitter and collector of the second transistor Q2, and the collector and emitter of the fourth transistor Q4. As a result, the above-mentioned constant current forward current IF is generated in the LED 1, so that the LED 1 is turned on.

Next, referring to FIG. 27, drive system power supply VLE
The operation of the LED drive circuit 281 when D is turned on will be described. First, at time t40, the drive system power supply VLED
It is assumed that the voltage of the drive system power supply VLED exceeds the drivable voltage Vth at time t41 to t42.

At this time, if the voltage externally applied to the point E is 0 V, at time t42, a lighting signal is generated, IF flows to LED1, and LED1 is lit. In addition, between time t42 and t46, the drive system power source VLE
Suppose D is stable.

Here, from time t44 to t45, E
When a high level signal is applied to the point once from the outside, the point B shifts to the low level, so that the LED 1 is turned off. Figure 2
7, the voltage of the drive system power supply VLED fluctuates from time t46 to t49, but since the constant current circuit 293 is used according to the present embodiment, the influence of the voltage fluctuation does not appear in IF and is stable. .

(Eighth Embodiment) FIG. 28 is a diagram showing the structure of an LED drive circuit 301 according to an eighth embodiment of the present invention. As shown in FIG. 28, the LED drive circuit 3
01 is an ON-OFF control circuit 291 that generates a lighting signal and a stop signal that are alternately repeated according to a pulse signal from the outside to control ON / OFF of the operation of the constant current circuit 313;
A constant current for inputting a lighting signal and a stop signal from the N-OFF control circuit 291 and supplying a constant current to the light emitting diode LED1 according to the lighting signal, while stopping the constant current supplied to the LED1 according to the stop signal. And a circuit 313. The current mirror circuit 215 and the reference voltage circuit 257 which constitute the constant current circuit 313 have been described above, and therefore their explanations are omitted.

Next, with reference to FIG. 28, the operation of the LED drive circuit 301 according to the present embodiment of the present invention will be described. Note that the time t is each timing shown in FIG. Now, at time t30, the drive system power supply VLED is applied to the LED drive circuit 301, and the description will be started assuming that the base voltage of the seventh transistor Q7 is in the low level state.

At this time, since the seventh transistor Q7 is in the off state, the LED1 and the constant current circuit 313 are
A current is flowing through. That is, the forward current IF = I
It is 1 + I2. (1) When the base voltage of the seventh transistor Q7 switches from the low level to the high level at the turn-off operation time t31, the seventh transistor Q7 switches from the off state to the on state,
The collector and the emitter of the seventh transistor Q7 become conductive.

As a result, a GND level stop signal is generated at the point B at the collector of the seventh transistor Q7, so that the drive system power source VLED is connected to the anode and cathode of LED1 and the emitter to collector of the first transistor Q1.
A current I1 flows from the collector of the seventh transistor Q7 via the emitter.

Since the voltage at the point B shown in FIG. 28 becomes the GND level, at the same time, the third and fourth transistors Q3 and Q3 are connected.
Q4 is turned off, and in response to this, the current I2 flowing through the second transistor Q2 of the current mirror circuit 215.
Is stopped and becomes 0, the first transistor Q
The current I1 flowing in 1 also becomes 0. As a result, the LED
The forward current of 1 becomes IF = 0, and the LED 1 is turned off.
When the light is turned off, the current IR2 flowing through the starting resistor R2 is as small as several μA, and therefore the LED1 does not light. Immediately after the base voltage of the seventh transistor Q7 switches from low level to high level, the collector voltage of the seventh transistor Q7 is
The ON period of the collector current Ic flowing between the emitters is determined by the parasitic capacitance of the semiconductor integrated circuit.

(2) Lighting Operation Next, at time t32, when the base voltage of the seventh transistor Q7 switches from the high level to the low level,
The seventh transistor Q7 switches from the ON state to the OFF state, the collector of the seventh transistor Q7 shifts to the open state, and the drive system power source VLED to LED1 and the starting resistor R
The collector of the seventh transistor Q7 becomes high level via 2 and a lighting signal appears at the point B. The starting resistance R
Since 2 has a resistance value on the order of several MΩ, the starting current has a value on the order of μA.

Since the voltage at the point B shown in FIG. 28 rises according to this starting current, the third and fourth transistors Q
3, Q4 turns on.

Furthermore, the third and fourth transistors Q
When Q3 and Q4 are turned on, the first and second transistors Q
Current flows from the emitter of 1, Q2 to the base,
The first and second transistors Q1 and Q2 are turned on. As a result, a current I1 flows from the drive system power source VLED through the anode and cathode of LED1, the emitter and collector of the first transistor Q1, the collector and emitter of the third transistor Q3, and the diodes D1 to Dm. At the same time, from the drive system power source VLED to the anode and cathode of LED1, the emitter to collector of the second transistor Q2, the collector to emitter of the fourth transistor Q4, and the resistor R1.
A current I2 flows through the.

Thus, at time t32, when the base voltage of the seventh transistor Q7 switches from the high level to the low level, the seventh transistor Q7 switches from the on state to the off state, and the collector of the transistor Q7 becomes open. , The activation current IR2 flows through the third transistor Q3, and activates the reference voltage circuit 257. As a result, the above-mentioned constant current forward current IF is generated in the LED 1, so that the LED 1 is turned on.

(Ninth Embodiment) FIG. 29 is a diagram showing the structure of an LED drive circuit 321 according to a ninth embodiment of the present invention. As shown in FIG. 29, the LED drive circuit 3
Reference numeral 21 denotes an ON-OFF control circuit 291 that generates a lighting signal and a stop signal that are alternately repeated according to a pulse signal from the outside to control ON / OFF of the operation of the constant current circuit 333;
A constant current for inputting a lighting signal and a stop signal from the N-OFF control circuit 291 and supplying a constant current to the light emitting diode LED1 according to the lighting signal, while stopping the constant current supplied to the LED1 according to the stop signal. And a circuit 333. The current mirror circuit 215, the reference voltage circuit 275, and the bandgap circuit 277 that form the constant current circuit 333 have been described above, and thus description thereof will be omitted.

Next, the operation of the LED drive circuit 321 according to the present embodiment of the present invention will be described with reference to FIG. Note that the time t is each timing shown in FIG. Now, at time t30, the drive system power supply VLED is applied to the LED drive circuit 321, and the description starts with the base voltage of the seventh transistor Q7 in the low level state. At this time, the seventh transistor Q
Since 7 is in the off state, current is flowing through the LED 1 and the constant current circuit 333. That is, the forward current IF = I1 + I2 + I3.

(1) At turn-off operation time t31, when the base voltage of the seventh transistor Q7 switches from low level to high level, the seventh transistor Q7 switches from off state to on state,
The collector and the emitter of the seventh transistor Q7 become conductive. As a result, a GND level stop signal is generated at the point B at the collector of the seventh transistor Q7, so that the drive system power supply VLED causes the anode and cathode of LED1, the emitter and collector of the first transistor Q1 and the collector of the seventh transistor Q7. A current I1 flows from the source through the emitter.

Since the voltage at the point B shown in FIG. 29 becomes the GND level, at the same time, the third and fourth transistors Q3 and Q3 are connected.
Q4 is turned off, and in response to this, the current I2 flowing through the second transistor Q2 of the current mirror circuit 215.
Is stopped and becomes 0, the first transistor Q
The current I1 flowing in 1 also becomes 0. At the same time, the supply of the current I2 flowing in the eighth transistor Q8 of the bandgap circuit 277 is stopped and becomes 0 in response to the turning off of the fourth transistor Q4, and accordingly, the ninth transistor Q9 is responded. The current I3 that was flowing into the memory also becomes zero. As a result, the forward current IF of LED1 becomes 0,
LED1 goes out.

When turned off, the current IR2 flowing through the starting resistor R2
Is a few μA, which is so small that LED1 does not light up. In addition,
Immediately after the base voltage of the seventh transistor Q7 switches from low level to high level, the seventh transistor Q7
The ON period of the collector current Ic flowing between the collector and the emitter of is determined by the parasitic capacitance of the semiconductor integrated circuit.

(2) Lighting Operation Next, at time t32, when the base voltage of the seventh transistor Q7 switches from high level to low level,
The seventh transistor Q7 switches from the ON state to the OFF state, the collector of the seventh transistor Q7 shifts to the open state, and the drive system power source VLED to LED1 and the starting resistor R
The collector of the seventh transistor Q7 becomes high level via 2 and a lighting signal appears at the point B. The starting resistance R
Since 2 has a resistance value on the order of several MΩ, the starting current has a value on the order of μA.

Since the voltage at the point B shown in FIG. 29 rises according to this starting current, the drive system power source VLED changes to LED1,
The base voltage of the third transistor Q3 is raised via the starting resistor R2 to turn on the third transistor Q3, and the current IR2 flows from the base to the emitter of the third transistor Q3 and further via the diodes D1 to Dm.

Since the voltage at the point B shown in FIG. 29 rises according to this starting current, the third and fourth transistors Q are generated.
3, Q4 turns on. Further, when the third and fourth transistors Q3 and Q4 are turned on, current flows from the emitters of the first and second transistors Q1 and Q2 toward the bases, and the first and second transistors Q1 and Q2 are turned on.

As a result, the drive system power source VLED to LED1
Of the second transistor Q2 from the emitter to the collector, the fourth transistor Q4 from the collector to the emitter, the first resistor R1, the eighth transistor Q8 from the collector to the emitter, and the resistor R5 to the current I
2 flows. At this time, since the eighth transistor Q8 is turned on, at the same time, the ninth transistor Q9 is turned on, and the drive system power source VLED changes the anode, cathode, and
G from the collector of the transistor Q9 via the emitter
A current I3 flows to ND.

Further, since the third transistor Q3 is turned on, the drive system power supply VLED to the anode and cathode of LED1, the emitter to collector of the first transistor Q1,
A current I1 flows from the collector of the third transistor Q3 to the emitter via the diodes D1 to Dm to GND.

Here, the forward current IF flowing in the LED 1
Is the sum of the currents flowing through the reference voltage circuit 275 and the bandgap circuit 277.

IF = I1 + I2 + I3 (24) As a result, the above-mentioned constant current forward current IF is generated in the LED 1, so that the LED 1 is turned on.

(Tenth Embodiment) FIG. 30 is a diagram showing the structure of an LED drive circuit 341 according to a tenth embodiment of the present invention. As shown in FIG. 30, the LED drive circuit 341 generates an ON / OFF control circuit 351 that ON / OFF controls the operation of the constant current circuit 353 by generating a lighting signal and a stop signal that are alternately repeated according to a pulse signal from the outside.
And a lighting signal and a stop signal from the ON-OFF control circuit 351, and the light emitting diode LE is input according to the lighting signal.
While supplying a constant current to D1, LED according to the stop signal
1 and a constant current circuit 353 that stops the constant current supplied to the first circuit. It should be noted that the current mirror circuit 215 and the bandgap circuit 21 that form the constant current circuit 353.
The description of 7 is omitted because it has been described above.

More specifically, the ON-OFF control circuit 351
Is a CMOS type 7-1 transistor Q7-1 and a seventh type
-2 transistor Q7-2. The gates of the 7-1th transistor Q7-1 and the 7-2th transistor Q7-2 are commonly connected, and a pulse signal from the outside is input to the gate and connected to the source of the 7-1th transistor Q7-1. One end of the activated resistance R2 is connected to the constant current circuit 3
First and second transistors Q1 and Q provided at 53
The emitter of 2 and the cathode of LED1 are commonly connected A
Connected to a point. Furthermore, the 7-1th transistor Q
The collector of the first transistor Q1, the collector and the base of the third transistor Q3 are commonly connected to a point B where the drain of the transistor 7-1 and the drain of the transistor 7-2 are commonly connected. The source of the 7-2nd transistor Q7-2 is connected to GND.

Next, the operation of the LED drive circuit 341 according to this embodiment of the present invention will be described with reference to FIG. The time t is each timing shown in FIG. At time t60, the drive system power supply VLED is applied to the LED drive circuit 341, and the seventh-
1-transistor Q7-1 and 7-2th transistor Q7-
The description will be started assuming that the gate voltage of 2 is in the low level state. At this time, since the 7-1th transistor Q7-1 is in the ON state, current flows through the LED 1 and the constant current circuit 353. That is, the forward current I
F = I1 + I2.

(1) When the gate voltage at the point E switches from the low level to the high level at the turn-off operation time t61, the 7-1th transistor Q
7-1 switches from the on state to the off state, and the 7-2
The transistor Q7-2 is switched from the off state to the on state, and the drain-source of the 7-2th transistor Q7-2 becomes conductive. As a result, a GND level stop signal is generated at the point B, so that the drive system power source VLED goes to L
The anode and cathode of ED1, the emitter to collector of the first transistor Q1, the 7-2th transistor Q7-2
A current I1 flows from the drain of the above to the GND via the source.

In response to this stop signal, the voltage at point B shown in FIG. 30 becomes the GND level, and at the same time, the third and fourth transistors Q3 and Q4 are turned off, and accordingly the current mirror circuit 215 is turned off. Second transistor Q
Since the supply of the current I2 flowing in 2 is stopped and becomes 0, the current I1 flowing in the first transistor Q1 also becomes 0. As a result, the forward current IF of LED1 becomes 0 and LED1 is turned off. Immediately after the gate voltage of the 7-2th transistor Q7-2 is switched from the low level to the high level, the semiconductor integrated circuit is operated during the ON period of the drain current Id flowing between the drain and the source of the 7-2th transistor Q7-2. It is determined by the parasitic capacitance of the circuit.

(2) Lighting Operation Next, at time t62, when the gate voltage at the point E switches from the high level to the low level, the 7-1th transistor Q7-1 switches from the off state to the on state, and the 7th- The two-transistor Q7-2 is switched from the on state to the off state, and the drain-source of the 7-1th transistor Q7-1 becomes conductive. As a result, the drive system power source V
The drain of the 7-1th transistor Q7-1 becomes high level from the LED through the LED1 and the starting resistor R2, and the lighting signal appears at the point B. Since the starting resistor R2 has a resistance value on the order of several MΩ, the starting current has a value on the order of μA.

Since the voltage at the point B shown in FIG. 30 rises according to this starting current, the third and fourth transistors Q
3, Q4 turns on. Further, when the third and fourth transistors Q3 and Q4 are turned on, current flows from the emitters of the first and second transistors Q1 and Q2 toward the bases, and the first and second transistors Q1 and Q2 are turned on.

As a result, the drive system power source VLED to LED1
A current I1 flows from the anode and cathode of the first transistor Q1, the emitter of the first transistor Q1 to the collector, and the collector of the third transistor Q3 to the emitter. At the same time, a current I2 flows from the drive system power source VLED through the anode and cathode of LED1, the emitter and collector of the second transistor Q2, and the collector and emitter of the fourth transistor Q4. As a result, the above-mentioned constant current forward current IF is generated in the LED 1, so that the LED 1 is turned on.

Next, referring to FIG. 32, drive system power supply VLE
The operation of the LED drive circuit 341 when D is turned on will be described. First, at time t70, drive system power supply VLED
It is assumed that the voltage of the drive system power supply VLED exceeds the drivable voltage Vth at times t71 to t72.

At this time, if the voltage externally applied to the point E is 0 V, at time t72, a lighting signal is generated, IF flows to LED1, and LED1 is lit. In addition, between time t72 and t76, the drive system power source VLE
Suppose D is stable.

At time t74 to t75, E
When a high level signal is applied to the point once from the outside, the point B shifts to the low level, so that the LED 1 is turned off. Figure 3
2, the voltage of the drive system power supply VLED fluctuates from time t76 to t79, but since the constant current circuit 353 is used according to the present embodiment, the influence of the voltage fluctuation does not appear in IF and is stable. .

(Eleventh Embodiment) FIG. 33 is a diagram showing the structure of an LED drive circuit 361 according to an eleventh embodiment of the present invention. As shown in FIG. 33, the LED drive circuit 361 generates an ON / OFF control circuit 351 that ON / OFF controls the operation of the constant current circuit 373 by generating a lighting signal and a stop signal that are alternately repeated according to a pulse signal from the outside.
And a lighting signal and a stop signal from the ON-OFF control circuit 351, and the light emitting diode LE is input according to the lighting signal.
While supplying a constant current to D1, LED according to the stop signal
1 and a constant current circuit 373 for stopping the constant current supplied to the first circuit. Note that the current mirror circuit 215 and the reference voltage circuit 257 which form the constant current circuit 373 have been described above, and therefore description thereof will be omitted.

Next, the operation of the LED drive circuit 361 according to this embodiment of the present invention will be described with reference to FIG. The time t is each timing shown in FIG. At time t60, the drive system power supply VLED is applied to the LED drive circuit 361, and the seventh-
1-transistor Q7-1 and 7-2th transistor Q7-
The description will be started assuming that the gate voltage of 2 is in the low level state. At this time, since the 7-1th transistor Q7-1 is in the ON state, current is flowing through the LED 1 and the constant current circuit 361. That is, the forward current I
F = I1 + I2.

(1) When the gate voltage at the point E switches from the low level to the high level at the turn-off operation time t61, the 7-1th transistor Q
7-1 switches from the on state to the off state, and the 7-2
The transistor Q7-2 is switched from the off state to the on state, and the drain-source of the 7-2th transistor Q7-2 becomes conductive. As a result, a GND level stop signal is generated at the point B, so that the drive system power source VLED goes to L
The anode and cathode of ED1, the emitter to collector of the first transistor Q1, the 7-2th transistor Q7-2
A current I1 flows from the drain of the above to the GND via the source.

In response to this stop signal, the voltage at point B shown in FIG. 33 goes to the GND level, and at the same time, the third and fourth transistors Q3 and Q4 are turned off, and accordingly the current mirror circuit 215 is turned off. Second transistor Q
Since the supply of the current I2 flowing in 2 is stopped and becomes 0, the current I1 flowing in the first transistor Q1 also becomes 0. As a result, the forward current IF of LED1 becomes 0 and LED1 is turned off. Immediately after the gate voltage of the 7-2th transistor Q7-2 is switched from the low level to the high level, the semiconductor integrated circuit is operated during the ON period of the drain current Id flowing between the drain and the source of the 7-2th transistor Q7-2. It is determined by the parasitic capacitance of the circuit.

(2) Lighting Operation Next, at time t62, when the gate voltage at the point E switches from the high level to the low level, the 7-1th transistor Q7-1 switches from the off state to the on state, and the 7th- The two-transistor Q7-2 is switched from the on state to the off state, and the drain-source of the 7-1th transistor Q7-1 becomes conductive. As a result, the drive system power source V
The drain of the 7-1th transistor Q7-1 becomes high level from the LED through the LED1 and the starting resistor R2, and the lighting signal appears at the point B. Since the starting resistor R2 has a resistance value on the order of several MΩ, the starting current has a value on the order of μA.

Since the voltage at the point B shown in FIG. 33 rises according to this starting current, the third and fourth transistors Q
3, Q4 turns on. Further, when the third and fourth transistors Q3 and Q4 are turned on, current flows from the emitters of the first and second transistors Q1 and Q2 toward the bases, and the first and second transistors Q1 and Q2 are turned on.

As a result, the drive system power source VLED to LED1
Current I1 flows through the anode and cathode of the first transistor Q1, the emitter of the first transistor Q1 to the collector, the collector of the third transistor Q3 to the emitter, and the diodes D1 to Dm. At the same time, a current I2 flows from the drive system power source VLED to the anode and cathode of LED1, the emitter and collector of the second transistor Q2, the collector and emitter of the fourth transistor Q4, and the resistor R1. As a result,
Since the above-mentioned constant current forward current IF is generated in the LED 1, the LED 1 is turned on.

(Twelfth Embodiment) FIG. 34 is a diagram showing the structure of an LED drive circuit 381 according to a twelfth embodiment of the present invention. As shown in FIG. 34, the LED drive circuit 381 generates an ON signal and a stop signal that are alternately repeated according to a pulse signal from the outside to control ON / OFF of the operation of the constant current circuit 393.
And a lighting signal and a stop signal from the ON-OFF control circuit 351, and the light emitting diode LE is input according to the lighting signal.
While supplying a constant current to D1, LED according to the stop signal
1 and a constant current circuit 393 for stopping the constant current supplied to the first circuit. The current mirror circuit 215, the reference voltage circuit 257, and the bandgap circuit 277 that form the constant current circuit 393 have been described above, and thus description thereof will be omitted.

Next, the operation of the LED drive circuit 381 according to the present embodiment of the present invention will be described with reference to FIG. The time t is each timing shown in FIG. Now, at time t60, the drive system power supply VLED is applied to the LED drive circuit 381, and
1-transistor Q7-1 and 7-2th transistor Q7-
The description will be started assuming that the gate voltage of 2 is in the low level state. At this time, since the 7-1th transistor Q7-1 is in the ON state, current is flowing through the LED 1 and the constant current circuit 393. That is, the forward current I
F = I1 + I2 + I3.

(1) When the gate voltage at the point E switches from the low level to the high level at the turn-off operation time t61, the 7-1th transistor Q
7-1 switches from the on state to the off state, and the 7-2
The transistor Q7-2 is switched from the off state to the on state, and the drain-source of the 7-2th transistor Q7-2 becomes conductive. As a result, a GND level stop signal is generated at the point B, so that the drive system power source VLED goes to L
The anode and cathode of ED1, the emitter to collector of the first transistor Q1, the 7-2th transistor Q7-2
A current I1 flows from the drain of the above to the GND via the source.

In response to this stop signal, the voltage at point B shown in FIG. 34 becomes GND level, and at the same time, the third and fourth transistors Q3 and Q4 are turned off, and accordingly the current mirror circuit 215 is turned off. Second transistor Q
Since the supply of the current I2 flowing in 2 is stopped and becomes 0, the current I1 flowing in the first transistor Q1 also becomes 0.

At the same time, in response to the turning off of the fourth transistor Q4, the eighth band gap circuit 277 is turned on.
Since the supply of the current I2 flowing in the transistor Q8 is stopped and becomes 0, accordingly, the ninth transistor Q9
The current I3 that was flowing into the memory also becomes zero. As a result, LED1
Forward current IF becomes 0 and the LED 1 is turned off.

Immediately after the gate voltage of the 7-2th transistor Q7-2 is switched from low level to high level, the ON period of the drain current Id flowing between the drain and source of the 7-2th transistor Q7-2 is , Is determined by the parasitic capacitance of the semiconductor integrated circuit.

(2) Lighting Operation Next, at time t62, when the gate voltage at the point E switches from the high level to the low level, the 7-1th transistor Q7-1 switches from the off state to the on state, and the 7th- The two-transistor Q7-2 is switched from the on state to the off state, and the drain-source of the 7-1th transistor Q7-1 becomes conductive. As a result, the drive system power source V
The drain of the 7-1th transistor Q7-1 becomes high level from the LED through the LED1 and the starting resistor R2, and the lighting signal appears at the point B. Since the starting resistor R2 has a resistance value on the order of several MΩ, the starting current has a value on the order of μA.

Since the voltage at the point B shown in FIG. 34 rises according to this starting current, the drive system power source VLED changes to LED1,
The base voltage of the third transistor Q3 is raised via the starting resistor R2 to turn on the third transistor Q3, and the current IR2 flows from the base to the emitter of the third transistor Q3 and further via the diodes D1 to Dm. Since the voltage at the point B shown in FIG. 34 rises according to this starting current,
The third and fourth transistors Q3 and Q4 are turned on.

Furthermore, the third and fourth transistors Q
When Q3 and Q4 are turned on, the first and second transistors Q
Current flows from the emitter of 1, Q2 to the base,
The first and second transistors Q1 and Q2 are turned on. As a result, the drive system power source VLED passes through the anode and cathode of LED1, the emitter and collector of the second transistor Q2, the collector and emitter of the fourth transistor Q4, the first resistor R1, the collector and emitter of the eighth transistor Q8, and the resistor R5. Then, the current I2 flows to GND.
At this time, since the eighth transistor Q8 is turned on, at the same time, the ninth transistor Q9 is turned on and the drive system power source VLED
From the anode and the cathode of LED1 and the collector of the ninth transistor Q9 through the emitter to the current I
3 flows.

Further, since the third transistor Q3 is turned on, the drive system power source VLED to the anode and cathode of LED1, the emitter to collector of the first transistor Q1,
A current I1 flows from the collector of the third transistor Q3 to the emitter via the diodes D1 to Dm to GND.
Here, the forward current IF flowing through the LED 1 is the sum of the currents flowing through the reference voltage circuit 275 and the bandgap circuit 277.

IF = I1 + I2 + I3 (25) As a result, the above-mentioned constant current forward current IF is generated in the LED 1, so that the LED 1 is turned on.

(Application Example 1) FIG. 35 is a diagram showing the structure of an LED drive device 401 to which the LED drive circuit 341 according to the tenth embodiment of the present invention described above is applied. Figure 3
As shown in FIG. 5, the LED drive device 401 drives the drive system power source V in accordance with control signals CNTY1 to CNTY4 input from the outside.
The switches SW1 to SW4, which are, for example, relay contacts or semiconductor switches, for turning on / off the connection lines supplied from the LEDs to the respective LEDs 11 to 44, and the switch SW1.
LED11 to 44 and LED1 respectively connected to
1 to 44 are connected in series to constant current circuits ICC1 to ICC4 for supplying a constant current, respectively.

Further, the constant current circuits ICC1 to IC4 have ON-OFF control circuits 411 to 41 for ON / OFF control according to pulse signals externally input to E1 to E4, respectively.
4 is connected. In this LED driving device 401, the switches SW1 to SW4 are controlled to be turned on / off in accordance with control signals CNTY1 to 4 which are externally input, LEDs to be lit are designated, and pulse signals externally input to E1 to E4, respectively. Since the lighting timing of the LED is designated according to the above, it can be used as a display device by setting the generation timing of the pulse signal to a frequency higher than the frequency at which flicker does not matter.

The constant current circuits ICC1 to ICC4 used in the LED driving device 401 are the LED driving circuits 201, 221, 241, 261 and 28 shown in the fourth to twelfth embodiments.
Any of 1,301,321,341,361,381 can be adopted. Moreover, since the constant current circuit has high impedance characteristics, the drive system power source VLED
The current value IF becomes constant even if the voltage of is increased.

Dynamically driven L as shown in FIG.
When it is assumed that a large number of LEDs having the same light intensity are mounted on the ED driving device 401, (1) any of the constant current circuits shown in the fourth to twelfth embodiments is used to drive the LEDs. Stable constant current forward current IF independent of system power supply VLED voltage and forward voltage VF
Therefore, it is extremely unlikely that the light intensity varies from LED to LED. Further, when the stop signal is output from the ON-OFF control circuit for ON / OFF controlling the LED, the constant current circuit is in the OFF state, so that no unnecessary current other than the current generated during lighting flows. It is possible to realize a highly efficient "constant current LED driver".

(2) A monolithic IC having high area efficiency can be realized by, for example, the above-mentioned ON-OFF control circuit and constant current circuit, and an LED defect detection function and a surge protection function can be added. Is.

(Common Effects in Fourth to Twelfth Embodiments) The LED drive circuits in the fourth to twelfth embodiments have the following common effects. In particular, compared to the conventional light emitting diode drive circuit, the lightness of the light emitting diode is stable, and the power supply efficiency can be improved.

(1) Since a stable constant current can be supplied to the LED 1 without depending on the voltage or VF of the driving system power source, even if the LED 1 is replaced with another LED, there is a possibility that the luminous intensity varies. Extremely low.

(2) When the stop signal is output from the ON-OFF control circuit, the constant current circuit is also turned off, and no unnecessary current flows. Therefore, a highly efficient LED drive circuit is provided. You can Note that, as shown in FIG. 26, in the seventh, eighth, and ninth embodiments, the starting resistance is several μA.
Current flows, but at a current level that does not affect the reduction in efficiency.

(3) Since the transistor used in the ON-OFF control circuit can reduce the Pc loss by less than that of the switching element Q7 that controls the ON / OFF of the LED.
It can contribute to the reduction of the amount of heat generation. (4) A monolithic IC with high area efficiency can be realized.

(5) Bipolar process and BiCMOS
Can be adapted to the process.

Compared with the above-described conventional light emitting diode drive circuit, the lightness of the light emitting diode can be stabilized and the power supply efficiency can be improved.

[0230]

According to the first aspect of the present invention, when the operation of the constant current circuit is ON-controlled by the switching element according to the pulse signal from the outside, the current is activated by activating the current mirror circuit by the activation resistor. The bandgap circuit receives the current generated by the current mirror circuit to generate a constant current having a positive temperature coefficient and supplies it to the switching element and the light emitting diode connected in series to the constant current circuit. Compared with the conventional light emitting diode drive circuit described above, the lightness of the light emitting diode is stable, and the power supply efficiency can be improved.

According to the second aspect of the present invention, when the operation of the constant current circuit is ON-controlled by the switching element in response to the pulse signal from the outside, the current mirror circuit is activated by the activation resistor to generate the current. Is generated, and the current generated from the current mirror circuit is received by the reference voltage circuit to generate the reference voltage and the constant current having the negative temperature coefficient is generated. It is possible to stabilize the brightness of the diode and contribute to the improvement of power supply efficiency.

According to the third aspect of the present invention, when the operation of the constant current circuit is on-controlled by the switching element according to the pulse signal from the outside, the current mirror circuit is activated by the activation resistance to generate the current. Then, the current generated by the current mirror circuit is received by the reference voltage circuit to generate the reference voltage, the constant current having a negative temperature coefficient is generated, and the constant current generated by the reference voltage circuit is received. Since the gap circuit generates a constant current having a temperature coefficient of a predetermined sign and magnitude, the lightness of the light emitting diode is more stable and contributes to the improvement of power supply efficiency as compared with the conventional light emitting diode drive circuit. be able to.

According to the twelfth aspect of the present invention, when a DC power source is applied to the light emitting diode and the constant current circuit connected in series, the current mirror circuit is activated by the activation resistance to generate a current, The bandgap circuit receives the current generated from the mirror circuit to generate a constant current having a positive temperature coefficient and supplies it to the light emitting diode connected in series to the constant current circuit. In comparison, the lightness of the light emitting diode is stable, and the power efficiency can be improved.

According to the thirteenth aspect of the present invention, when a DC power source is applied to the light emitting diode and the constant current circuit connected in series, the current mirror circuit is activated by the activation resistance to generate a current, The current generated from the mirror circuit is received by the reference voltage circuit to generate the reference voltage and the constant current having a negative temperature coefficient is generated, so that the brightness of the light emitting diode is stable compared to the conventional light emitting diode drive circuit. In addition, it can contribute to the improvement of power supply efficiency.

According to the fourteenth aspect of the present invention, when a DC power source is applied to the light emitting diode and the constant current circuit connected in series, the current mirror circuit is activated by the activation resistance to generate a current, The reference voltage circuit receives the current generated from the mirror circuit to generate the reference voltage, the constant current having a negative temperature coefficient is generated, and the bandgap circuit receives the constant current generated from the reference voltage circuit. Since a constant current having a temperature coefficient of a predetermined sign and magnitude is generated, the brightness of the light emitting diode can be further stabilized and the power supply efficiency can be improved as compared with the conventional light emitting diode drive circuit. .

According to the sixteenth aspect of the present invention, a start trigger and a stop signal that are alternately repeated according to a pulse signal from the outside are generated, and a constant current is supplied to the light emitting diode according to the start trigger, while the stop signal is stopped. Since the constant current supplied to the light emitting diode is stopped according to the signal, the lightness of the light emitting diode is stable and contributes to the improvement of power supply efficiency, as compared with the conventional light emitting diode drive circuit described above. You can

According to the twentieth aspect of the present invention, a lighting signal and a stop signal which are alternately repeated according to a pulse signal from the outside are generated, and a constant current is supplied to the light emitting diode according to the lighting signal, while the stop signal is stopped. Since the constant current supplied to the light emitting diode is stopped according to the signal, the lightness of the light emitting diode is stable and contributes to the improvement of power supply efficiency, as compared with the conventional light emitting diode drive circuit described above. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an LED drive circuit 11 according to a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the LED drive circuit 11 according to the first embodiment of the present invention.

FIG. 3 is a constant current circuit 1 provided in the LED drive circuit 11.
6 is a graph showing the characteristics of the DC power supply Vcc and the forward current IF in FIG.

FIG. 4 is a graph showing characteristics of a forward current IF and a junction temperature Tj in the constant current circuit 13.

FIG. 5 is a diagram showing a configuration of a modification 1 of the LED drive circuit 11 according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a modified example 2 of the LED drive circuit 11 according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of an LED drive circuit 21 according to a second embodiment of the present invention.

FIG. 8 is a constant current circuit 2 provided in the LED drive circuit 21.
6 is a graph showing the characteristics of the DC power supply Vcc and the forward current IF in FIG.

9 is a graph showing the characteristics of the forward current IF and the junction temperature Tj in the constant current circuit 23. FIG.

FIG. 10 is a diagram showing a configuration of an LED drive circuit 31 according to a third embodiment of the present invention.

FIG. 11 shows characteristics of the first resistance R1 and the third resistance R3 and the junction temperature Tj when the constant current circuit 33 provided in the LED drive circuit 31 according to the third embodiment of the present invention is monolithically formed. It is a graph which shows.

FIG. 12 is a graph showing the characteristics of the forward voltage VF and the junction temperature Tj in the constant current circuit 33.

FIG. 13 is an LE according to the first to third embodiments of the present invention.
It is a figure which shows the structure of the LED drive device 41 which applied D drive circuit 11,21,31.

FIG. 14 is an LE according to the first to third embodiments of the present invention.
It is a figure which shows the structure of the LED drive device 51 which applied D drive circuit 11,21,31.

FIG. 15 is a diagram showing a conventional LED drive circuit 101.

16 is a timing chart for explaining the operation of the conventional LED drive circuit 101. FIG.

FIG. 17 is a diagram showing a conventional LED drive circuit 102.

FIG. 18 is a timing chart for explaining the operation of the conventional LED drive circuit 102.

FIG. 19 is a diagram showing a configuration of an LED drive circuit 201 according to a fourth embodiment of the present invention.

FIG. 20 is a timing chart for explaining the operation of the LED drive circuit 201 according to the fourth embodiment of the present invention.

21 is a graph showing the characteristics of the drive system power supply VLED and the forward current IF in the constant current circuit provided in the LED drive circuit 201. FIG.

FIG. 22 is a diagram showing a configuration of Modification 1 of the LED drive circuit 201 according to the fourth embodiment of the present invention.

FIG. 23 is a diagram showing a configuration of an LED drive circuit 241 according to a fifth embodiment of the present invention.

FIG. 24 is a diagram showing a configuration of an LED drive circuit 261 according to a sixth embodiment of the present invention.

FIG. 25 is a diagram showing a configuration of an LED drive circuit 281 according to a seventh embodiment of the present invention.

FIG. 26 is a timing chart for explaining the operation of the LED drive circuit 281 according to the seventh embodiment of the present invention.

27 is a graph showing the characteristics of the drive system power supply VLED and the forward current IF in the constant current circuit provided in the LED drive circuit 281. FIG.

FIG. 28 is a diagram showing a configuration of an LED drive circuit 301 according to an eighth embodiment of the present invention.

FIG. 29 is a diagram showing a configuration of an LED drive circuit 321 according to a ninth embodiment of the present invention.

FIG. 30 is a diagram showing a configuration of an LED drive circuit 341 according to a tenth embodiment of the present invention.

FIG. 31 is a timing chart for explaining the operation of the LED drive circuit 341 according to the tenth embodiment of the present invention.

32 is a graph showing the characteristics of the drive system power supply VLED and the forward current IF in the constant current circuit provided in the LED drive circuit 341. FIG.

FIG. 33 is a diagram showing a configuration of an LED drive circuit 361 according to an eleventh embodiment of the present invention.

FIG. 34 is a diagram showing a configuration of an LED drive circuit 381 according to a twelfth embodiment of the present invention.

FIG. 35 is an L according to fourth to twelfth embodiments of the present invention.
It is a figure which shows the structure of the LED drive device 401 which applied the ED drive circuit.

[Explanation of symbols]

11,21,31 LED drive circuit LED1 light emitting diode 12,13,14,23,33 constant current circuit Q7 switching element 15,16,19 current mirror circuit 17,18,37 bandgap circuit 27,35 reference voltage circuit 201, 221, 241, 261, 281, 301, 3
21,341,361,381 LED drive circuit LED1 Light emitting diode 213,233,251,273,293,313,3
33, 353, 361, 393 Constant current circuit 215, 235 Current mirror circuit 217, 237, 277 Bandgap circuit 257, 275 Reference voltage circuit

Claims (32)

[Claims] 1. A constant current circuit for supplying a constant current having a positive temperature coefficient to a light emitting diode, and a constant current circuit connected in series to the light emitting diode and the constant current circuit connected in series to receive a pulse signal from the outside. And a switching element that controls the operation of the constant current circuit on and off,
A constant current circuit comprising: a current mirror circuit as a current source; a starting resistor for starting the current mirror circuit; and a current generated by the current mirror circuit. And a bandgap circuit for generating a constant current having a positive temperature coefficient, and a light emitting diode drive circuit. 2. A constant current circuit for supplying a constant current having a negative temperature coefficient to the light emitting diode, and a constant current circuit connected in series to the light emitting diode and the constant current circuit connected in series to receive a pulse signal from the outside. And a switching element that controls the operation of the constant current circuit on and off,
A constant current circuit comprising: a current mirror circuit as a current source; a starting resistor for starting the current mirror circuit; and a current generated by the current mirror circuit. And a reference voltage circuit for generating a constant current having a negative temperature coefficient, and a light emitting diode drive circuit. 3. A constant current circuit for supplying a constant current having a temperature coefficient of a predetermined sign and magnitude to the light emitting diode, and the light emitting diode and the constant current circuit connected in series, which are connected in series to each other from the outside. A switching element for controlling the on / off operation of the constant current circuit according to the pulse signal of
A constant current circuit comprising: a current mirror circuit as a current source; a starting resistor for starting the current mirror circuit; and a current generated by the current mirror circuit. Generating a reference voltage and generating a constant current having a negative temperature coefficient, and a constant current having a predetermined sign and magnitude for receiving the constant current generated from the reference voltage circuit. And a bandgap circuit for generating the light emitting diode drive circuit. 4. The constant current circuit, wherein the current mirror circuit has first and second PNP type transistors, the emitters are commonly connected, the bases are commonly connected, and the base of the second transistor is further provided. A collector is connected, the bandgap circuit has NPN-type third and fourth transistors, the bases are commonly connected, and the collector of the first transistor and the collector and base of the third transistor are connected The collector of the second transistor is connected to the collector of the fourth transistor, the emitter of the third transistor is connected to one end of the first resistor, and the emitter of the fourth transistor is connected to the other of the first resistor. The starting resistor is connected between the base of the second transistor and one end of the first resistor. The light emitting diode drive circuit according to claim 1, wherein 5. In the constant current circuit, the current mirror circuit has first and second PNP type transistors, emitters are commonly connected, bases are commonly connected, and further, a base of the second transistor is provided. A collector is connected, the reference voltage circuit has NPN-type third and fourth transistors, the bases are commonly connected, and the collector of the first transistor and the collector and base of the third transistor are connected. The collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected to the first through at least one diode.
Is connected to one end of the resistor, the emitter of the fourth transistor is connected to the other end of the first resistor, and the start-up resistor is between the base of the second transistor and one end of the first resistor. The light emitting diode drive circuit according to claim 2, wherein the light emitting diode drive circuit is connected. 6. The constant current circuit, wherein the current mirror circuit has first and second PNP type transistors, the emitters are commonly connected, the bases are commonly connected, and the base of the second transistor is further provided. A collector is connected, the reference voltage circuit has NPN-type third and fourth transistors, the bases are commonly connected, and the collector of the first transistor and the collector and base of the third transistor are connected. The collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected to the anode of the first diode of the m diodes connected in series. The emitter of the transistor is connected to the other end of the first resistor, and the bandgap circuit is an NPN-type fifth and A sixth transistor, the bases of which are commonly connected, and one end of the first resistor is connected to the collector and the base of the fifth transistor;
The emitter of the transistor is connected to the collector of the sixth transistor, and the emitter of the fifth transistor is connected to the third
Is connected to the other end of the resistor, the emitter of the sixth transistor is connected to one end of the third resistor, and is connected to the cathode of the m-th diode of the m diodes connected in series, The light emitting diode drive circuit according to claim 3, wherein is connected between the base of the second transistor and one end of the third resistor. 7. The light emitting diode drive circuit according to claim 4, wherein the fourth transistor provided in the bandgap circuit has a multi-emitter. 8. The light emitting diode drive circuit according to claim 6, wherein the sixth transistor provided in the bandgap circuit has a multi-emitter. 9. The first resistor and the third resistor limit the current flowing through the fourth transistor and the fifth transistor and adjust the temperature coefficient of the current flowing through the sixth transistor. 7. The light emitting diode drive circuit according to claim 6. 10. The switching element is any one of a piper transistor, a FET, and an IGBT.
4. The light emitting diode drive circuit according to claim 1, wherein the light emitting diode drive circuit is a semiconductor switching element composed of two elements. 11. The light emitting diode drive circuit according to claim 1, which is monolithically formed as a semiconductor integrated circuit. 12. A light emitting diode drive circuit comprising a constant current circuit for supplying a constant current having a positive temperature coefficient to a light emitting diode, wherein the light emitting diode and the constant current circuit are connected in series. The current circuit includes a current mirror circuit as a current source, a starting resistor for starting the current mirror circuit, and a band for receiving a current generated from the current mirror circuit and generating a constant current having a positive temperature coefficient. A light emitting diode drive circuit comprising: a gap circuit. 13. A light emitting diode drive circuit comprising a constant current circuit for supplying a constant current having a negative temperature coefficient to the light emitting diode, wherein the light emitting diode and the constant current circuit are connected in series. The current circuit has a current mirror circuit as a current source, a starting resistor for starting the current mirror circuit, a current generated from the current mirror circuit to generate a reference voltage, and a negative temperature coefficient. A reference voltage circuit for generating a constant current, and a light emitting diode drive circuit. 14. A light emitting diode drive circuit comprising a constant current circuit for supplying a constant current having a temperature coefficient of a predetermined sign and magnitude to the light emitting diode, wherein the light emitting diode and the constant current circuit are connected in series. The constant current circuit includes a current mirror circuit as a current source, a starting resistor for starting the current mirror circuit, a current generated from the current mirror circuit, a reference voltage, and a negative voltage. A reference voltage circuit for generating a constant current having a temperature coefficient of, and a bandgap circuit for receiving a constant current generated from the reference voltage circuit and generating a constant current having a temperature coefficient of a predetermined sign and magnitude. A light-emitting diode drive circuit having. 15. The light emitting diode drive circuit according to claim 12, which is monolithically formed as a semiconductor integrated circuit. 16. An on / off control circuit for alternately generating a start trigger and a stop signal according to a pulse signal from the outside, and an on / off control circuit which is connected in series to the light emitting diode and which supplies the start trigger and the stop signal from the on / off control circuit. And a constant current circuit that supplies a constant current to the light emitting diode in response to the start trigger and stops the constant current supplied to the light emitting diode in response to the stop signal. Light emitting diode drive circuit. 17. The constant current circuit inputs a start trigger and a stop signal from the on / off control circuit, and a current mirror circuit for supplying a constant current to the light emitting diode, and the current mirror circuit operates in response to the start trigger. A bandgap circuit that receives the generated current and starts generating a constant current having a positive temperature coefficient, and stops the supply of the constant current to the current mirror circuit in response to the stop signal. The light emitting diode drive circuit according to claim 16. 18. The constant current circuit inputs a start trigger and a stop signal from the current mirror circuit that supplies a constant current to the light emitting diode, and the on / off control circuit, and the current mirror circuit operates in response to the start trigger. A reference voltage circuit that receives the generated current and generates a reference voltage to start generating a constant current having a negative temperature coefficient, and that stops supplying the constant current to the current mirror circuit in response to the stop signal. The light emitting diode drive circuit according to claim 16, further comprising: 19. The constant current circuit inputs a start trigger and a stop signal from the on / off control circuit, the current mirror circuit supplying a constant current to the light emitting diode, and the current mirror circuit according to the start trigger. A reference voltage circuit that receives the generated current and generates a reference voltage to start generating a constant current having a negative temperature coefficient, and that stops supplying the constant current to the current mirror circuit in response to the stop signal. 17. The light emitting diode drive circuit according to claim 16, further comprising a bandgap circuit that receives a constant current generated from the reference voltage circuit and generates a constant current having a temperature coefficient of a predetermined sign and magnitude. . 20. An ON / OFF control circuit for alternately generating a lighting signal and a stop signal in response to a pulse signal from the outside, and an ON / OFF control circuit connected in series to the ON / OFF control circuit for supplying the lighting signal and the stop signal. A constant current circuit for inputting and supplying a constant current to the light emitting diode in response to the lighting signal, and for stopping the constant current supplied to the light emitting diode in response to the stop signal. Light emitting diode drive circuit. 21. The constant current circuit inputs a lighting signal and a stop signal from the on / off control circuit and a current mirror circuit which supplies a constant current to the light emitting diode, and the current mirror circuit operates in response to the lighting signal. A bandgap circuit that receives the generated current and starts generating a constant current having a positive temperature coefficient, and stops the supply of the constant current to the current mirror circuit in response to the stop signal. 21. The light emitting diode drive circuit according to claim 20. 22. The constant current circuit inputs a lighting signal and a stop signal from the on / off control circuit and a current mirror circuit which supplies a constant current to the light emitting diode, and the current mirror circuit operates in response to the lighting signal. A reference voltage circuit that receives the generated current and generates a reference voltage to start generating a constant current having a negative temperature coefficient, and that stops supplying the constant current to the current mirror circuit in response to the stop signal. The light emitting diode drive circuit according to claim 20, further comprising: 23. The constant current circuit inputs a lighting signal and a stop signal from the on / off control circuit, and a current mirror circuit for supplying a constant current to the light emitting diode, and the current mirror circuit operates according to the lighting signal. A reference voltage circuit that receives the generated current and generates a reference voltage to start generating a constant current having a negative temperature coefficient, and that stops supplying the constant current to the current mirror circuit in response to the stop signal. 21. The light emitting diode drive circuit according to claim 20, further comprising a bandgap circuit that receives a constant current generated from the reference voltage circuit and generates a constant current having a temperature coefficient of a predetermined sign and magnitude. . 24. In the constant current circuit, the current mirror circuit has first and second PNP type transistors, emitters thereof are commonly connected, bases thereof are commonly connected, and further, a base of the second transistor. A collector is connected, the bandgap circuit has NPN-type third and fourth transistors, the bases are commonly connected, and the collector of the first transistor and the collector and base of the third transistor are connected The collector of the second transistor is connected to the collector of the fourth transistor, the emitter of the third transistor is connected to one end of the first resistor, and the emitter of the fourth transistor is connected to the other of the first resistor. 22. The light emitting diode drive circuit according to claim 17, which is connected to an end. 25. In the constant current circuit, the current mirror circuit has first and second PNP-type transistors, emitters are commonly connected, bases are commonly connected, and bases of the second transistors are further provided. A collector is connected, the reference voltage circuit has NPN-type third and fourth transistors, the bases are commonly connected, and the collector of the first transistor and the collector and base of the third transistor are connected. The collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected to the first through at least one diode.
23. The light emitting diode drive circuit according to claim 18, wherein the resistor is connected to one end of the resistor, and the emitter of the fourth transistor is connected to the other end of the first resistor. 26. In the constant current circuit, the current mirror circuit has first and second PNP type transistors, emitters thereof are commonly connected, bases thereof are commonly connected, and further, a base of the second transistor. A collector is connected, the reference voltage circuit has NPN-type third and fourth transistors, the bases are commonly connected, and the collector of the first transistor and the collector and base of the third transistor are connected. The collector of the second transistor is connected to the collector of the fourth transistor, and the emitter of the third transistor is connected to the anode of the first diode of the m diodes connected in series. The emitter of the transistor is connected to the other end of the first resistor, and the bandgap circuit is an NPN-type eighth and And a ninth transistor, the bases of which are commonly connected, one end of the first resistor is connected to the collector and the base of the eighth transistor, and the second transistor is connected to the second resistor.
The emitter of the transistor is connected to the collector of the ninth transistor, and the emitter of the eighth transistor is connected to the fifth transistor.
Connected to the other end of the resistor, the emitter of the ninth transistor is connected to one end of the fifth resistor, and is connected to the cathode of the m-th diode of the m diodes connected in series. Claim 19 or 2 characterized by
3. The light emitting diode drive circuit described in 3. 27. The on / off control circuit has NPN-type fifth, sixth, and seventh transistors, a pulse signal from the outside is input to the base of the seventh transistor, and the power source is a third resistor. Connected to the collector through the emitter, the emitter is grounded through the fourth resistor,
The connection point between the collector of the transistor and the third resistor is connected to the anode of the diode through the capacitor, and the cathode of the diode is connected to the base of the fifth transistor, while the emitter of the seventh transistor is connected. And a fourth resistor are connected to the base of the sixth transistor, and are connected to a common connection point between the emitters of the first and second transistors of the constant current circuit and the cathode of the light emitting diode, or to the power supply. The activated resistance is connected to the collector of the fifth transistor, and the common connection point of the emitter of the fifth transistor and the collector of the sixth transistor is connected to the collector of the first transistor and the constant current circuit. The collector and base of the third transistor are commonly connected, and the emitter of the sixth transistor is grounded. Claim, characterized in 16,24,2
The light emitting diode drive circuit according to 5 or 26. 28. The on / off control circuit has an NPN-type seventh transistor, a pulse signal from the outside is input to the base of the seventh transistor, and the first and second transistors of the constant current circuit are provided. A common connection point between the emitter of the light emitting diode and the cathode of the light emitting diode, or a starting resistor connected to the power supply, is connected to the collector of the seventh transistor, and the collector of the seventh transistor is connected to the collector of the first transistor and the collector of the first transistor. 27. The light emitting diode drive circuit according to claim 20, wherein the collector and the base of the third transistor of the constant current circuit are commonly connected, and the emitter of the seventh transistor is grounded. 29. The on / off control circuit has a CMOS type 7-1 transistor and a 7-2 transistor, and is externally connected to the commonly connected gates of the 7-1 and 7-2 transistors. From the source of the 7-1th transistor whose starting resistance is connected to the common connection point of the emitters of the first and second transistors of the constant current circuit and the cathode of the light-emitting diode And the drain of the 7-1th transistor and the drain of the 7-2th transistor are commonly connected, the collector of the first transistor and the collector of the third transistor of the constant current circuit. And the bases are commonly connected, and the source of the 7th-2nd transistor is grounded.
The light emitting diode drive circuit according to 0, 24, 25, or 26. 30. The light emitting diode drive circuit according to claim 24, wherein the fourth transistor provided in the bandgap circuit has a multi-emitter. 31. The light emitting diode drive circuit according to claim 26, wherein the ninth transistor provided in the bandgap circuit has a multi-emitter. 32. The light emitting diode driving circuit according to claim 16, wherein the semiconductor integrated circuit is monolithically formed.