JP2001008443A - Current drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption in a current drive circuit which drives a current drive element by supplying a current to the element from a power source, when the circuit drives the element. SOLUTION: A current drive circuit is provided with an LED 2, which emits light receiving a current and a coil 3 connected in series with the LED 2. The circuit is also provided with a diode 4, which supplies a counter electromotive force generated in the coil 3 to the LED 3 and is connected in parallel with the LED 2 and coil 3 and a switching element 5, which switches the output voltage of a DC power source 1 so that a pulse voltage is impressed upon the LED 2, the coil 3, and the diode 4. The cathode of the diode 4 is connected to the positive electrode of the DC electrode 1, so that a reverse bias is impressed on the diode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current driving circuit for driving a current driving element by supplying a current from a power supply, and more particularly, to a light emitting diode (Light Em) as a light emitting element.
It relates to a current driving circuit that drives an itting diode (hereinafter referred to as an LED) and a miniature bulb.

[0002]

2. Description of the Related Art FIG. 8 shows a schematic configuration of a conventional current drive circuit provided with, for example, an LED as a current drive element. In FIG. 8, a conventional current drive circuit includes a DC power supply 100 and an LE
A current limiting resistor 101 is connected between the current limiting resistor 101 and the D102. By adjusting the resistance value of the resistor 101, even if the output voltage value of the DC power
A predetermined operating current can be supplied to the power supply 102. For example, when driving an _LED 102 having an operation voltage V _LED of 2 V and an operation current I _LED of 10 mA,
If the output voltage V _DD of the DC power supply 100 is 10 V, a resistance element having a resistance value R = 800Ω may be used for the resistor 101, and if the output voltage V _DD is 20 V, the resistance value R = 180
A resistance element of 0Ω may be used.

Considering the power consumption in this circuit, when the output voltage V _DD is 10 V and the operating current I _LED is 10 m
In the case of A, the power consumption of the entire circuit is 0.1 W (= V _DD ×
I _LED ), but the power consumption of the _LED 102 is 0.0
2W (= V _LED × I _LED ). The remaining 0.08 W is converted into heat or the like by the resistor 101 and consumed. In this example, the power use efficiency is only about 20%.

Further, when the output voltage V _DD is 20 V and the operating current I _LED is 10 mA, the power consumption of the entire circuit is 0.
Although 2W (= V _DD × I _LED ), the power consumption of the _LED 102 is only 0.02W (= V _LED × I _LED ).
The remaining 0.18 W is consumed by the resistor 101, and in this example, only about 10% of the power use efficiency is obtained.

Thus, the operating current I of the LED 102
_{When the LED} is fixed at, for example, 10 mA, the DC power supply 100
If the output voltage value is selected as a high voltage, the resistance value of the resistor 101 must be increased. As a result, the power consumption of the resistor 101 increases, and the power use efficiency decreases. As described above, the conventional current driving circuit has a simple configuration with a small number of components, but has a problem that the energy lost by the resistor 101 is large and the power supply efficiency cannot be increased.

[0006]

As a suggestion of a current drive circuit which solves this problem, Japanese Patent Laid-Open Publication No.
There is a light emitting element driving device for a pulse oximeter disclosed in Japanese Patent Application Publication No. 2 (JP-A) No. 2 (1995). A schematic configuration of a current driving circuit based on the disclosed light emitting element driving device for a pulse oximeter will be described with reference to FIG. The current driving circuit shown in FIG.
LED as a current drive element that operates by supplying current
102 and a coil (inductor) 103 connected in parallel to the LED 102. A power supply unit that applies a pulse voltage to the LED 102 and the coil 103 is provided. The power supply unit includes a DC power supply 100 and a switching element 104 that functions as a switch that switches between application and non-application of the output voltage of the DC power supply 100. are doing. The switching element 104 includes, for example, a switching transistor and an oscillator. Note that the LED 102
Has a cathode connected to the positive electrode of the DC power supply 100 to apply a reverse bias voltage.

In the conventional current driving circuit having such a configuration, when the switching element 104 operates based on a predetermined light emission timing, the output voltage of the DC power supply 100 is intermittently applied to the coil 103 and the LED 102. FIG. 10 shows a control pulse (switching pulse) SW applied to the switching element 104 and the coil 10
3 and the current flowing through the LED 102 are illustrated. FIG.
0 (a), the switch is turned on at the falling edge of the switching pulse SW input to the switching element 104, and the DC voltage V
_DD is applied to coil 103 and LED 102. LED
Since 102 is reverse biased, as shown in FIG. 10C, when the switching pulse SW is in the "L" state, no current flows when the current I _LED = 0, but as shown in FIG. A current _IL flows through the coil 103. This current I _L
Changes with time t. Assuming that the inductance of the coil 103 is L, I _L = (V _DD / L) t.
Increases to _{I L = 0~I L = i 0} .

Next, as shown in FIG. 10A, a switching pulse S
When the switch is turned off at the rising edge of W, the application of the voltage from the DC power supply 100 is cut off, and a back electromotive force is generated in the coil 103. Current I _L flows through the coil 103 by the counter electromotive force, the current value is reduced to _{I L = i 0 ~I L =} 0 varies with time t. At this time, as shown in FIG. 10C, the operating current I _LED flows in the forward direction of the _LED 102 while decreasing from I _LED = i _{0 to} I _LED = 0, and the _LED 102 emits light.

As described above, according to the conventional current driving circuit based on the above publication, the LED 102 emits light using the back electromotive force of the coil 103.
00 can be used, and power consumption can be reduced as compared with a current driving circuit using a resistor.

However, in this conventional current driving circuit,
As is clear from FIG. 10C, since the LED 102 does not light when the reverse bias is applied, the LED 1 is continuously turned on.
02 cannot be turned on.

In general, the withstand voltage of the LED 102 in the reverse bias is about 6 V at most. Therefore, this conventional current drive circuit has no problem as long as a battery or the like having a low output voltage (for example, 6 V or less) is used. However, when a power supply that outputs a relatively high voltage (6 V or more) is used, LE is used.
D102 may be destroyed. However,
In many cases, LEDs used for various applications have to use a power supply that outputs a high voltage of 6 V or more that is used for driving another element or the like as a driving power supply. For example, a power supply having an output voltage of about several tens of volts (volts) to about 20 volts may be used in the electric system of general home appliances, but a DC-DC converter or the like is incorporated to transform a DC voltage and supply the LED to an LED. Doing so complicates circuit design and increases the number of circuit components, resulting in higher costs.
Also, when driving an element including an LED at a relatively low output voltage, the junction resistance in a circuit affects the LED.
There is a possibility that the light emitting operation of the device becomes unstable.

An object of the present invention is to provide a current driving circuit capable of reducing power consumption when driving a current driving element. Another object of the present invention is to provide a current drive circuit that can select a power supply voltage without depending on the breakdown voltage characteristics of the current drive element.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a current driving element which operates by supplying a current, a coil connected in series with the current driving element, and a counter electromotive force generated in the coil to the current driving element. The present invention is attained by a current driving circuit having a diode for supplying and a power supply section for intermittently applying a voltage to at least the current driving element and the coil.

According to the current driving circuit of the present invention, the current driving element is operated by applying the output voltage from the power supply unit, energy is stored in the coil, and the output voltage from the power supply unit is cut off. After that, the current driving element can be operated using the back electromotive force of the coil. Therefore, it is possible to drive the current driving element with small power consumption by eliminating the power consumption loss due to the resistance as in the conventional current driving circuit.

In the above-mentioned current drive circuit according to the present invention, the power supply section may include a DC power supply and a switching element for switching an output voltage of the DC power supply.
Further, the current driving element may be a light emitting element. In the above current drive circuit of the present invention, the diode may include:
The current driving element and the coil are connected in parallel. Then, one end of the diode may be connected to a tap provided on the coil. Alternatively, the diode may be connected in parallel to the switching element.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A current driving circuit according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a current drive circuit according to the present embodiment. The current drive circuit in FIG. 1 includes an LED 2 as a current drive element that emits light when a current is supplied, and a coil 3 connected in series to the LED 2. LED2
The diode 4 is connected in parallel with the coil 3. As will be described in detail later, the diode 4 is provided to supply the back electromotive force generated in the coil 3 to the LED 2.

A power supply unit for applying a pulse voltage to the LED 2, the coil 3, and the diode 4 is provided.
The power supply unit includes a DC power supply 1 and a switching element 5 that functions as a switch for switching application / non-application of the output voltage of the DC power supply 1. The switching element 5 includes, for example, a switching transistor and an oscillator. The diode 4 has a cathode connected to the positive electrode of the DC power supply 1 so that a reverse bias is applied.

In the current driving circuit according to the present embodiment having such a configuration, when the switching element 5 operates based on a desired light emission timing for causing the LED 2 to emit light, the output voltage of the DC power supply 1 is changed to the coil 3 side and the diode 4 Is applied intermittently. FIG. 2 shows a control pulse (switching pulse) S applied to the switching element 5.
W and a current flowing through the coil 3 and the LED 2 are illustrated. As shown in FIG. 2A, when the switch is turned on at the falling edge of the switching pulse SW input to the switching element 5, the DC voltage V
_DD is applied to the coil 3 and the diode 4. Since the diode 4 is reverse-biased, no current flows.
As shown in (b) and (c), the switching pulse S
When W is in the “L” state, the current I _L flows through the coil 3, and the same amount of current I _LED flows through the LED 2 connected in series with the coil 3, causing the LED 2 to emit light. The current I _L and the current value of the current I _LED change with time t, and the current I _{L of the} coil 3 becomes ₀ to i ₀
And the current I _LED flowing through _{LED 2} also becomes 0
Ｉi ₀ .

Next, as shown in FIG. 2A, when the switch is turned off at the rising edge of the switching pulse SW input to the switching element 5 and the application of the voltage from the DC power supply 1 is cut off, the coil 3 generates a back electromotive force. Due to this back electromotive force, a current _IL flows through the coil 3, and the current value changes with time t, so that I _L = i ₀ to I _L
L = 0. The back electromotive voltage generated in the circuit is LED
2 and the diode 4 are applied in the forward direction.
Current I _L of the coil 3 flows in LED2 and the diode 4. Therefore, as shown in FIG. 2C, the current I _LED flows through the _LED 2 while decreasing from I _LED = i _{0 to} I _LED = 0.
LED2 emits light.

As described above, according to the current drive circuit of this embodiment, when the switch is turned on by the switching element 5, the LED 2 emits light by applying the output voltage from the DC power supply 1, and the switch is turned off. , The back electromotive force of the coil 3 is used to
Is made to emit light. Therefore, it is possible to reduce the power consumption loss that occurs in the current driving circuit using the resistor as in the related art, so that the LED can emit light with low power consumption.

Further, as is apparent from FIG. 2C, since the LED 2 can be turned on regardless of the on / off state of the switch of the switching element 5, the LED 2 can be turned on continuously. For example, even if the switching cycle becomes longer, light emission with less flicker can be obtained.

Further, since no reverse bias is applied to the LED 2, it is not necessary to separately prepare a power supply circuit capable of applying a voltage in accordance with the withstand voltage performance of the reverse bias of the LED 2.
A current driving element can be manufactured with a simple circuit configuration by directly using a power supply voltage already provided in a device on which the ED is mounted. As described above, according to the present embodiment, it is possible to reduce power consumption when driving a current driving element, and to select a power supply voltage without depending on withstand voltage characteristics of the current driving element. become.

FIG. 3 shows the effect of reducing power consumption in the current driving circuit according to the present embodiment in comparison with a conventional current driving circuit. The horizontal axis indicates the output voltage of the DC power supply, and the vertical axis indicates power consumption. In FIG. 3, the operating voltage V _LED of the _LED is 2 V and the operating current I
_{The LED} was set to 10 mA. Therefore, in the current drive circuit according to the present embodiment, the inductance L of the coil 3 is adjusted according to the output voltage of the DC power supply 1. Further, in the conventional current driving circuit using the resistor shown in FIG. 8, the resistance value of the resistor 101 is adjusted according to the output voltage of the DC power supply 100. As shown in FIG. 3, the voltage versus power consumption line (α) of the current drive circuit according to the present embodiment has a constant and low power consumption of 0.02 regardless of the output voltage value of DC power supply 1.
W maintains a _{(= V LE D × I LED} ).

On the other hand, the voltage vs. power consumption line (β) of the conventional current driving circuit using the resistor 101
As the output voltage of the resistor 101 increases, the resistance of the resistor 101 also increases, resulting in an increase in power consumption. FIG. 3 also shows the voltage versus power consumption line (γ) of the conventional current drive circuit using the coil described with reference to FIG. 9, but as described above, the reverse bias applied to the LED is 6 V. Not compared because it cannot be exceeded. As described above, according to the present embodiment, it is possible to realize a current driving circuit that consumes the least power when the emission luminance of the LED is the same in at least the region where the output voltage of the DC power supply is 6 V or more.

Next, a modification of the current driving circuit according to the present embodiment will be described with reference to FIG. Note that the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The current drive circuit shown in FIG. 4 is characterized in that a tap 6 that can be connected at a position other than between both ends of the coil is provided. The cathode side of the diode 4 is connected to the tap 6. By adjusting this tap 6,
The current I flowing through the coil 3 when the circuit switch is turned on
_At time t1 when _L increases from ₀ to i0, the switch is turned off and a back electromotive force is generated in the coil 3, and the coil 3 and LE
D2, the current I _L flowing through the diode 4 is a time t2 which decreases to i ₀ ~0 so can be substantially the same. By providing the tap 6, especially when a self-excited oscillation circuit is provided in the current drive circuit as the switching element 5, the application of the output voltage of the DC power supply 1 is performed.
Since the duty ratio for switching off can be set to about 50%, there is an advantage that circuit design is simplified.

Next, another modified example of the current driving circuit according to the present embodiment will be described with reference to FIG. FIG.
The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted. The current drive circuit shown in FIG. 5 is characterized in that the connection of the diode 4 connected in parallel to the coil 3 and the LED 2 in FIG. This configuration is such that when the switch is turned on by the switching element 5,
The output voltage from the DC power supply 1 is applied and the coil 3 and L
When a current flows through the ED 2 and the switch is turned off, a current due to the back electromotive force in the coil 3 flows through the LED 2 and the diode 4.

In the circuit configuration shown in FIG. 1, when the switch of the switching element 5 is turned off, the current caused by the back electromotive force of the coil 3 flows through the closed loop of the coil 3, the LED 2, and the diode 4. However, in the circuit configuration shown in FIG. 5 of this modification, when the switch of the switching element 5 is turned off, the diode 4 is connected in parallel with the switching element 5, so that the voltage from the DC power supply 1 is also applied. A current flows from the DC power supply 1 to the DC power supply 1 via the coil 3, the LED 2, and the diode 4. As described above, according to the present modification, the power supply from the DC power supply 1 can be always received. Therefore, even when the back electromotive force of the coil 3 is small, the power loss due to various resistances including the junction resistance in the circuit is very small. You can design circuits without worrying about them.

Next, an example of the switching element 5 used in the current drive circuit according to the present embodiment will be described with reference to FIG. Components other than the switching element 5 are the same as those shown in FIG. The switching element 5 is, for example, a DC power supply 1
Has a switching transistor 7 whose voltage is applied to the collector. A resistor 8 for inputting a switching pulse SW from an oscillator 9 is connected to a base of the switching transistor 7. By outputting the switching pulse SW as shown in FIG. 2A from the oscillator 9, switching by the switching transistor 7 can be performed.

Next, still another modification of the current drive circuit according to the present embodiment will be described with reference to FIG. FIG.
7A shows a schematic configuration of a current driving circuit provided with a self-excited oscillation circuit, and FIG. 7B shows a circuit configuration in a block 20 in FIG. 7A. In FIG. 7A, the positive terminal of the DC power supply 1 is connected to the input terminal V _IN of the block 20, and the output terminal LCD _OUT of the block 20 is connected to the anode of the LED 2. The cathode side of the LED 2 is maintained at the ground potential together with the ground (ground) terminal G of the block 20. The switching element 5 shown in FIG. 7A does not have an oscillator for supplying a switching pulse SW, and has a function of only switching a switch in response to, for example, a single ON / OFF signal from the outside. ing. In FIG. 7B, the coil (L1) 3 is connected to a resistor R9.
Is connected in series with LED2 through a diode (D
1) 4 is connected between the connection point between the transistor Q1 and the coil 3 and the ground terminal G to connect the coil 3 and the LED 2
Are connected in parallel.

Further, resistors R2 to R5, R7 to R9, transistors Q2 to Q6, and a Zener diode DZ1,
DZ2 forms a constant current control circuit and a low voltage protection circuit. Although not described in detail, an oscillation circuit is configured by the transistors Q1 and Q7, the resistors R1 and R20, and the diode D2 as illustrated. In addition,
The diode D2 is used for stabilizing the oscillation.

When the switch is turned on by the switching element 5, the output voltage from the DC power supply 1 is applied to the oscillation circuit in the block 20, and oscillation is started at a predetermined cycle and duty cycle. As a result, the output voltage from the DC power supply 1 is applied to the coil 3 intermittently. When a voltage is applied from the DC power supply 1, the coil 3 and L
Currents I _L and I _LED flow through ED 2, respectively, and _LED 2 emits light. When no voltage is applied from DC power supply 1, LED 2 emits light due to the back electromotive force generated in coil 3. Therefore, even if the switching pulse SW from the external oscillator 9 is not supplied to the switching transistor 7 as shown in FIG. 5 and the like, in the current drive circuit according to the present modification, as long as the switching element 5 is turned on. The LED 2 can be kept lit.

The present invention is not limited to the above embodiment, but can be variously modified. For example, in the above embodiment, an LED which is one of the light emitting elements is described as an example of the current driving element. However, the present invention is not limited to this, and the present invention may be applied to various circuits including a transistor driven by current supply. It is possible to apply In the above embodiment, the DC power supply and the switching element are used. However, the present invention is not limited to this, and a unipolar voltage source or the like can be used.

Further, the current driving circuit for causing the LED to emit light in the above-described embodiment has a wide variety of uses, such as displaying an operation mode of various electronic devices and home appliances, and using a plurality of L-modes.
The EDs can be arranged in a plane and used as a surface-emitting display device. For example, indoors, it is used as an alarm display on a production line of a factory, various information boards, and the like, and outdoors, as a destination display or traffic information display board in a station yard. The present invention is applicable to LED driving circuits in such various applications, and
It is possible to obtain a large power-saving effect by using this in a device that is frequently used.

[0034]

As described above, according to the present invention, it is possible to reduce the power consumption when driving the current driving element.
Further, according to the present invention, the power supply voltage can be selected without depending on the breakdown voltage characteristics of the current driving element. Therefore, the circuit configuration of the current drive circuit can be simplified.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a current drive circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a switching circuit applied to a switching element in a current driving circuit according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating an example of a pulse SW and a current flowing through a coil 3 and an LED 2.

FIG. 3 is a diagram showing the effect of reducing power consumption in the current drive circuit according to one embodiment of the present invention, in comparison with a conventional current drive circuit.

FIG. 4 is a diagram showing a schematic configuration of a modified example of the current drive circuit according to one embodiment of the present invention;

FIG. 5 is a diagram showing a schematic configuration of another modified example of the current drive circuit according to the embodiment of the present invention;

FIG. 6 is a diagram showing an example of a switching element 5 used in the current drive circuit according to one embodiment of the present invention.

FIG. 7 is a diagram showing a schematic configuration of still another modified example of the current drive circuit according to one embodiment of the present invention;

FIG. 8 is a diagram showing a schematic configuration of a conventional current drive circuit including an LED as a current drive element.

FIG. 9 is a diagram showing a schematic configuration of a conventional current driving circuit based on the disclosed light emitting element driving device for a pulse oximeter.

10 is a diagram illustrating an example of a switching pulse SW applied to the switching element 104 of the current drive circuit illustrated in FIG. 9 and an example of a current flowing through the coil 103 and the LED 102.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 100 DC power supply 2, 102 LED 3 Coil 4 Diode 5, 104 Switching element 6 Tap 7 Switching transistor 8, 101 Resistance 9 Oscillator

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (6)

[Claims] A current driving element that operates by supplying a current; a coil connected in series with the current driving element; a diode for supplying a back electromotive force generated in the coil to the current driving element; A current drive circuit, comprising: a power supply section for intermittently applying a voltage to the current drive element and the coil. 2. The current drive circuit according to claim 1, wherein the power supply unit includes a DC power supply, and a switching element for switching an output voltage of the DC power supply. . 3. The current driving circuit according to claim 1, wherein the current driving element is a light emitting element. 4. The current driving circuit according to claim 1, wherein the diode is connected in parallel to the current driving element and the coil. Current drive circuit. 5. The current driving circuit according to claim 4, wherein one end of said diode is connected to a tap provided on said coil. 6. The current drive circuit according to claim 2, wherein the diode is connected in parallel with the switching element.