JP2000347613A - Driving circuit for light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving circuit for a light emitting diode which can save an electric power and downsize. SOLUTION: A voltage detection circuit 4 outputs a voltage detection signal S4 which is H when a cathode voltage of a light emitting diode 1 is above 0.7 V (minimum level voltage which a constant electric current driving circuit 2 can supply a constant electric current), and whish is L when the cathode voltage is below 0.7 V. After a one-chip microcomputer 5 receives a start signal for a power supply S6 which indicates a control start, it increases a power supply voltage Vcc every 0.05 V from 0 V until the voltage detection signal S4 changes to H from L. When the voltage detection signal S4 changes to H, the one-chip microcomputer 5 stops a voltage increase of the power supply voltage Vcc and finishes a set-up of the power supply voltage Vcc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driving circuit for a display device such as a light emitting diode.

[0002]

2. Description of the Related Art FIG. 13 is a block diagram of a conventional light emitting diode driving circuit disclosed in Japanese Patent Application Laid-Open No. 61-201483. As shown in FIG. 13, the anode of the light emitting diode 1 is connected to the positive terminal of the power supply 17 and one end of the resistor 18, and the cathode is connected to the collector (output node N2) of the NPN bipolar transistor 16.

The base of the transistor 16 is connected to the node N1, and the emitter is connected to the negative terminal of the power supply. The other end of the resistor 18 is connected to one end of the resistor 13 and the constant voltage diode 15
The other end of the resistor 13 is connected to the node N1.

The anode of the diode 14 is connected to the node N 1, and the cathode is connected to the negative terminal of the power supply 17.
The anode of the constant voltage diode 15 is also connected to the negative terminal of the power supply 17.

[0005] In the example of FIG. 13, a constant current driving circuit is constituted by the resistor 18, the resistor 13, the diode 14, the constant voltage diode 15 and the transistor 16, and the voltage fluctuation of the power supply 17 is clamped by the constant voltage diode 15. Therefore, the base voltage of the transistor 16 is always kept constant, and the constant current drive circuit can perform a constant current operation.
If the configuration of FIG. 13 is roughly shown by a circuit block, the configuration shown in FIG. 14 is obtained. In the configuration of FIG. 13, the constant current drive circuit also uses the power supply 17 as the operation power supply. However, the operation is not affected even if another power supply is used. Therefore, the case where another power supply (not shown) is used.

In FIG. 14, the power supply voltage of the power supply 17 is V
Assuming that cc and the output voltage of the constant current drive circuit 2, that is, the voltage of the cathode of the light emitting diode is Vob, the forward voltage Vf of the light emitting diode is expressed by the following equation (I).

Vf = Vcc-Vob (I) The threshold value corresponding to the forward voltage at which the light emitting diode is turned on is Vf
Assuming that t, if Vft ≦ Vf, the light is turned on and Vf <Vf
If it is t, it will not be lit.

Generally, the constant current drive circuit 2 outputs the output voltage Vob
Does not operate normally at 0 V, and the output voltage Vob needs to be higher than a predetermined voltage.

With this configuration, it is possible to operate normally when the output voltage Vob of the constant current drive circuit 2 is 1.0 V or more. Also, the forward voltage Vf of the light emitting diode is usually
In this conventional example, the threshold voltage Vft of the light emitting diode 1 is assumed to be in the range of 1.6 V to 2 V.

The power supply voltage Vcc of the power supply 17 required under these conditions
Is obtained, the output voltage Vob of the constant current drive circuit 2 becomes 1.
To normally light all the light emitting diodes at 0 V or more, it is necessary to consider the maximum threshold voltage Vft of 2.0 V. As shown in the following equation (II), the power supply voltage Vcc is 3.
0 V or more is required.

Vcc ≧ Vob + Vft (max) = 1.0 + 2.0 = 3.0 V (II) Here, assuming that the current flowing through the light emitting diode 1 is 0.1 A, the light emitting diode 1 and the driving circuit (2 , 17)
, The power consumption P is: P = 3.0 V × 0.1 A =
0.3 W.

When driving a light emitting diode whose light emitting diode 1 has the lowest threshold voltage Vft of Vft = 1.6 V, the output voltage Vob of the constant current driving circuit 2 is 1.4 V１Vo.
b = 3.0V−1.6V = 1.4V｝, and the power Pc consumed by the constant current drive circuit 2 is 0.14W ｛Pc =
1.4V × 0.1A = 0.14W｝.

Since the constant current drive circuit 2 operates normally when the output voltage Vob is at least 1.0 V, a voltage exceeding 1.0 V, in this case 0.4 V is an unnecessary voltage, which is wastefully consumed by the drive circuit. Will be done. In this case, the power wastefully consumed by the constant current drive circuit 2 is 0.04W ｛0.4V ×
0.1A = 0.04W｝.

[0014]

The conventional light emitting diode driving circuit uses a fixed voltage power supply, and the threshold voltage Vft of the forward voltage of the light emitting diode varies by several tens of percent. Therefore, in order to normally light all the light emitting diodes, it is necessary to set the power supply voltage Vcc in consideration of the maximum value of the threshold voltage Vft, and it is necessary to set the power supply voltage Vcc higher.

When driving a light emitting diode having an average threshold voltage Vft with a power supply voltage Vcc set higher, the power consumption of the constant current drive circuit is increased more than necessary because an extra voltage is added to the constant current drive circuit. There was a problem that would be.

For example, the threshold voltage Vft of the forward voltage is 1.6.
When driving the light emitting diode of V, as described above, the power supply voltage Vcc needs to be 3.0 V in consideration of the maximum threshold voltage Vft (2.0 V).
4V ｛Vob = Vcc−Vf = 3.0V−1.6V = 1.
When a voltage of 4 V is applied, the power consumption of the constant current drive circuit becomes 0.14 W.

The constant current drive circuit has an output voltage Vob of 1.0
It operates normally at V and the power consumption of the constant current drive circuit at that time is 0.1 W, so 0.04 W of 0.14 W is wasted.

When driving a collective lamp in which a large number of light emitting diodes are wired in series, the power consumption of the driving circuit increases in proportion to the number of light emitting diodes. Therefore, heat radiating means such as heat radiating fins are required, which is a major obstacle to downsizing and power saving of the constant current drive circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a light emitting diode drive circuit that is reduced in size and power.

[0020]

Means for Solving the Problems Claim 1 according to the present invention.
The driving circuit of the light emitting diode described above, a light emitting diode, a power supply voltage for light emission of the light emitting diode is supplied to an anode of the light emitting diode, the power supply voltage is variably settable, and a cathode of the light emitting diode And a constant current driving means for supplying a constant current to the light emitting diode when the voltage at the cathode becomes an output voltage and the output voltage is equal to or higher than a predetermined voltage.

According to a second aspect of the present invention, the light emitting diode driving circuit further includes a light emitting diode characteristic value detecting means capable of detecting a light emitting diode characteristic value serving as an index indicating whether or not the light emitting diode emits light normally. I have.

According to a third aspect of the present invention, in the light emitting diode drive circuit, during the power supply voltage adjusting process, the light emitting diode characteristic value obtained by the light emitting diode characteristic value detection means while changing the power supply voltage is based on the light emitting diode characteristic value. There is further provided a power supply voltage adjusting means for finally setting the power supply voltage at the lowest level within a range in which the light emitting diode normally emits light.

5. A light emitting diode driving circuit according to claim 4, wherein said light emitting diode includes a plurality of light emitting diodes, and said constant current driving means includes a plurality of constant current driving means corresponding to said plurality of light emitting diodes on a one-to-one basis. Contains.

According to a fifth aspect of the present invention, the light emitting diode driving circuit is provided for each of the plurality of light emitting diodes on a one-to-one basis, and each of the plurality of light emitting diodes normally emits light. There is further provided a plurality of light emitting diode characteristic value detecting means capable of detecting a light emitting diode characteristic value serving as an index indicating whether or not there is a light emitting diode characteristic value.

According to a sixth aspect of the present invention, in the light emitting diode driving circuit, the plurality of light emitting diode characteristic values obtained by measuring the plurality of light emitting diode characteristic value detecting means while changing the power supply voltage during the power supply voltage adjusting process. And a power supply voltage adjusting means for finally setting the power supply voltage at the lowest level within a range in which all of the plurality of light emitting diodes normally emit light.

[0026] In the light emitting diode driving circuit according to claim 7, the light emitting diode characteristic value detecting means includes voltage detecting means capable of detecting the voltage of the cathode of the light emitting diode as the light emitting diode characteristic value.

9. The light emitting diode driving circuit according to claim 8, wherein said light emitting diode includes a light emitting diode which normally emits light when said constant current flows, and wherein said light emitting diode characteristic value detecting means includes a light emitting diode of said cathode of said light emitting diode. A voltage detection unit that outputs a comparison result between a voltage and the predetermined voltage as a voltage detection signal, the light emitting diode characteristic value includes the voltage detection signal, and the power supply voltage adjustment unit performs the power supply voltage adjustment processing, Means for setting, based on the voltage detection signal obtained while changing the power supply voltage, the power supply voltage when the voltage at the cathode becomes equal to the predetermined voltage.

According to a ninth aspect of the present invention, in the light emitting diode drive circuit, the light emitting diode characteristic value detecting means includes a current detecting means capable of detecting a current flowing through the light emitting diode as the light emitting diode characteristic value.

11. A light emitting diode driving circuit according to claim 10, wherein said light emitting diode includes a light emitting diode which normally emits light when a predetermined current flows, and wherein said light emitting diode characteristic value detecting means determines a current flowing through said light emitting diode. A current detection unit that outputs a result of comparison with the predetermined current as a current detection signal; the light emitting diode characteristic value includes the current detection signal; and the power supply voltage adjustment unit performs the power supply voltage adjustment processing during the power supply voltage adjustment processing. Means for setting the power supply voltage when the current flowing through the light emitting diode becomes equal to the predetermined current based on the current detection signal while changing the voltage.

The light emitting diode driving circuit according to claim 11, wherein the light emitting diode characteristic value detecting means includes a luminance detecting means capable of detecting the light emission luminance of the light emitting diode as the light emitting diode characteristic value.

13. A light emitting diode driving circuit according to claim 12, wherein said light emitting diode characteristic value detecting means detects the luminance of the light emitting diode and a reference luminance of a level at which the light emitting diode emits light normally. The power supply voltage adjusting means includes a luminance detecting means for outputting as a signal, the light emitting diode characteristic value includes the luminance detecting signal, and the power supply voltage adjusting processing, based on the luminance detecting signal while changing the power supply voltage. Means for setting the power supply voltage when the light emission luminance is equal to the reference luminance.

The light emitting diode driving circuit according to claim 13, wherein a total value of the current flowing through the plurality of light emitting diodes is compared with a total reference value determined to be normal for the plurality of light emitting diodes to emit light. Current detection means for outputting as a detection signal, and when the total value of the current flowing through the light emitting diode becomes equal to a predetermined total reference value based on the current detection signal while changing the power supply voltage during the power supply voltage adjustment process. Power supply voltage adjusting means for setting the power supply voltage;

[0033]

<First Embodiment> FIG. 1 is a block diagram showing a configuration of a light emitting diode driving circuit according to a first embodiment of the present invention. As shown in the figure, the driving circuit of the light emitting diode according to the first embodiment has the light emitting diode 1,
The external control device 6 includes a constant current drive circuit 2, a variable DC power supply 3 with a signal control function, a voltage detection circuit 4, and a one-chip microcomputer 5. The one-chip microcomputer 5 of the light-emitting diode drive circuit of the first embodiment is used. An external device that can be connected to

The anode of the light emitting diode 1 is connected to the positive terminal (+) of the variable DC power supply 3 having a signal control function to receive the power supply voltage Vcc, and the cathode is connected to the constant current drive circuit 2.
Is connected to the output node N2. The constant current drive circuit 2 is connected to the cathode of the light emitting diode 1 and the negative terminal (-) of the variable DC power supply 3 having a signal control function, and supplies a constant current when the output voltage Vob which is the cathode voltage of the light emitting diode 1 is higher than a predetermined voltage. Perform the operation.

When a predetermined voltage is applied to the light emitting diode 1 in a forward direction, a current flows and light is emitted. FIG. 2 shows the relationship between the forward voltage Vf and the current If of a general light emitting diode. As shown in FIG. 2, the light emitting diode 1 has a voltage Vf = 1.8.
The current starts to flow at V, and If = f near 2.05 V, If =
A current of 0.1 A flows.

The forward voltage Vf of the light emitting diode is several tens of percent.
If = 0.1 A, V shown in FIG.
Assuming that the light emitting diode of f = 2.05V is an average diode, the forward voltage Vf varies from about 1.8V to 2.2V with respect to the current If = 0.1A.

The constant current drive circuit 2 has a predetermined output voltage Vob
When the voltage becomes higher, the circuit performs a constant current supply operation of flowing a preset constant current to the light emitting diode regardless of the output voltage. FIG. 3 shows an example of the relationship between the output voltage Vob and the current If. As shown in FIG. 3, the current reaches the set current value when Vob = 0.7 V, and supplies a constant current to the light emitting diode 1 regardless of the voltage when Vob ≧ 0.7 V.

The variable DC power supply 3 with a signal control function is provided with an electronic volume and the like.
Can be changed.

The voltage detection circuit 4 determines "H" (high) based on whether or not the cathode voltage of the light emitting diode 1 is equal to or higher than a predetermined voltage (the lowest voltage at which the constant current drive circuit 2 can supply a constant current). ) Or "L" (Low) voltage detection signal S4. Here, a voltage detection signal S4 of "H" is output when the cathode voltage of the light emitting diode 1 is 0.7 V or higher, and "L" when the cathode voltage is 0.7 V or lower. As the voltage detection circuit 4, a configuration including a reference voltage generation circuit for generating a reference voltage of 0.7 V and a voltage comparator for comparing the reference voltage with the cathode voltage of the light emitting diode 1 can be considered.

The one-chip microcomputer 5 is a general one-chip microcomputer, and a power control start signal S for instructing the start of control.
6, the voltage detection signal S4 from the voltage detection circuit 4
The power supply voltage control signal S5 for controlling the power supply voltage is sent to the variable DC power supply 3 with an external control circuit in accordance with the above.

The external control device 6 is composed of a personal computer or the like, and can send a power control start signal S6 for instructing the start of power supply voltage adjustment to the one-chip microcomputer 5.

In such a configuration, the light emitting diode 1 has a threshold voltage Vf corresponding to a current If of 0.1 A.
A method of adjusting the power supply voltage Vcc of the variable DC power supply 3 with a signal control function when a light emitting diode having t of 2.05 V is provided will be described.

When a power control start signal S6 for instructing the start of control from the external control device 6 is sent to the one-chip microcomputer 5,
The one-chip microcomputer 5 is a variable DC power supply 3 with a signal control function.
, A power supply voltage control signal S5 instructing 0 V is output, and the power supply voltage Vcc output from the positive terminal of the variable DC power supply with signal control function 3 is initialized to 0 V.

Then, based on the voltage detection signal S4, if the voltage detection signal S4 is "L", the one-chip microcomputer 5 controls the power supply voltage to instruct the power supply voltage to be increased in predetermined steps, for example, in steps of 0.05V. The signal S5 is sent to the variable DC power supply 3 with a signal control function. Thereafter, similarly, the power supply voltage control signal S5 for instructing the increase of the power supply voltage is continuously output to the variable DC power supply with signal control function 3 until the voltage detection signal S4 changes from "L" to "H".

The power supply voltage Vcc increases in steps of 0.05 V. If the power supply voltage Vcc is 1.8 V or less, no current flows through the light emitting diode 1 and the output voltage Vob maintains 0 V. All Vcc will be applied to the light emitting diode 1. At this time, since the voltage detection signal S4 is maintained at "L", the one-chip microcomputer 5 sends the power supply voltage control signal S5 instructing the variable DC power supply 3 with signal control function to increase the power supply voltage to the variable DC power supply 3 with signal control function. Then, the power supply voltage Vcc is further increased.

When the power supply voltage Vcc exceeds 1.8 V, a current starts to flow through the light emitting diode 1 to light up the light emitting diode 1 lightly. The output voltage Vob becomes a voltage corresponding to the current flowing through the light emitting diode 1. For example, when the power supply voltage Vcc is 2.05 V, the diode Vf = 1.95 V, Vob = 0.1 V, If
= 0.01A.

At this time, since the voltage detection signal S4 is still "L", the one-chip microcomputer 5 sends the power supply voltage control signal S5 instructing the variable DC power supply 3 with a signal control function to increase the power supply voltage. The power supply voltage Vcc of the variable DC power supply with control function 3 is increased.

Thereafter, when the power supply voltage Vcc reaches 2.75 V, Vf = 2.05 V, Vob = 0.7 V, If
= 0.1 A, and the light emitting diode 1 normally lights up brightly. Here, for the first time, the voltage detection signal S4 changes from “L” to “H”. When the voltage detection signal S4 becomes "H", the one-chip microcomputer 5 stops sending the power supply voltage control signal S5 instructing the power supply voltage increase to the variable DC power supply with signal control function 3, and completes the adjustment of the power supply voltage Vcc. . At this time, the power consumption Pc of the constant current drive circuit 2 is 0.07 W ｛Pc
= 0.7V × 0.1A = 0.07W｝, and the power consumption can be suppressed to the minimum within a range in which the constant current drive circuit 2 operates normally.

That is, by setting the power supply voltage Vcc when the output voltage Vob becomes 0.7 V while changing the power supply voltage Vcc, low power consumption operation of the constant current drive circuit 2 is realized. Furthermore, the power saving of the constant current drive circuit 2 allows the heat dissipation means such as the radiation fins to be omitted, which leads to the downsizing of the constant current drive circuit 2.

Even if the power supply voltage Vcc is increased to 2.75 V or more, the current If hardly increases due to the operation of the constant current drive circuit 2. For example, the power supply voltage is increased to 2.75 V in consideration of the maximum threshold voltage Vft. When the voltage is set to 95 V, in the average light-emitting diode 1, Vf of the diode = 2.05 V and Vob =
0.90V, If = 0.1A. That is, almost all the rise of the power supply voltage Vcc becomes the rise voltage of the output voltage Vob of the constant current drive circuit 2. The power consumption of the drive circuit at this time is Pc = 0.9 V × 0.1 A = 0.09 W.

The light emitting diode 1 shown in FIG.
When a light emitting diode whose threshold voltage Vft corresponding to f = 0.1 A is 2.2 V is used, the power supply voltage Vcc is adjusted to 2.9 V by performing the voltage adjustment by the power supply voltage control signal S5 of the one-chip microcomputer 5 described above. At this point, the light emitting diode 1 normally lights up, and the voltage detection signal S4 changes from "L" to "H". Therefore, the power supply voltage Vcc of the variable DC power supply 3 with a signal control function is set to 2.9V. You. At this time, Vf = 2.2 V, Vob = 0.7 V, If = 0.
1A.

Also in this case, the power consumption P of the constant current drive circuit 2
c is the minimum 0.07W ｛Pc = 0.7V × 0.1A =
0.07 W}, and the power consumption can be suppressed to the minimum within a range in which the constant current drive circuit 2 operates normally.

When a plurality of light emitting diodes are connected in parallel to one variable DC power supply with a signal control function, the cathode of each of the plurality of light emitting diodes is connected to a constant current driving circuit, and the output of each constant current driving circuit is connected. A voltage detection circuit is provided for detecting a voltage, and when the voltage detection signals of all the voltage detection circuits become “H”, the adjustment of the power supply voltage of the variable DC power supply with a signal control function is completed. Thereby, the power supply voltage Vcc can be adjusted to the lowest power supply voltage within a range in which all of the plurality of light emitting diodes driven by one variable DC power supply 3 having the signal control function can be turned on.

<Embodiment 2> FIG. 4 is a block diagram showing a configuration of a light emitting diode driving circuit according to Embodiment 2 of the present invention. As shown in the figure, the light emitting diode drive circuit of the second embodiment includes a light emitting diode 1, a constant current drive circuit 2, a variable DC power supply 7, and a voltmeter 8.

The anode of the light emitting diode 1 is connected to the positive terminal (+) of the variable DC power supply 7 so that the power supply voltage V
cc, and the cathode is the output node N of the constant current drive circuit 2.
2 is connected. The constant current drive circuit 2 is provided between the negative terminal of the light emitting diode 1 and the variable DC power supply 7, and performs a constant current supply operation based on the output voltage Vob, which is the cathode voltage of the light emitting diode 1, as in the first embodiment.

The variable DC power supply 7 has no function of changing the power supply voltage Vcc by an external signal. To change the power supply voltage Vcc, it is necessary to manually adjust a variable resistor (not shown) provided.

The voltmeter 8 is connected to the cathode of the light emitting diode 1, and can measure the cathode voltage of the light emitting diode 1, that is, the output voltage Vob of the node N2 of the constant current drive circuit 2.

In such a configuration, as in the first embodiment, the variable DC power supply 7 in the case where a light emitting diode having a threshold voltage Vft of 2.05 V corresponding to a current If of 0.1 A is provided as in the first embodiment. A method of adjusting the power supply voltage Vcc will be described.

When the power supply voltage adjuster adjusts the variable resistor of the variable DC power supply 7 to gradually increase the power supply voltage Vcc from 0 V, when the power supply voltage Vcc reaches 2.75 V, Vf
= 2.05V, Vob = 0.7V, If = 0.1A, the voltmeter 8 indicates 0.7V, and the light emitting diode normally lights up brightly. When the voltmeter 8 indicates 0.7 V, the power supply voltage adjuster stops adjusting the variable DC power supply 7 and completes the adjustment of the power supply voltage. As a result, the constant current drive circuit 2
Can be suppressed to the lowest power consumption within a range where the device operates normally.

When the power supply voltage Vcc is further increased, the current If hardly increases due to the operation of the constant current drive circuit 2 as in the first embodiment, and almost all the rise of the power supply voltage Vcc is a constant current. The output voltage Vob of the drive circuit 2 corresponds to a rise.

The light emitting diode 1 shown in FIG.
When a light emitting diode whose threshold voltage Vft corresponding to f = 0.1 A is 2.2 V is used, the light emitting diode normally lights up when the power supply voltage Vcc is increased to 2.9 V, as in Embodiment 1. The voltmeter 8 indicates 0.7V. When the voltmeter 8 indicates 0.7 V, the power supply voltage adjuster stops adjusting the variable DC power supply 7 and completes the adjustment of the power supply voltage. As a result, the power consumption can be suppressed to the minimum within a range where the constant current drive circuit 2 operates normally.

When a plurality of light emitting diodes are connected in parallel to one variable DC power supply, the cathode of each of the plurality of light emitting diodes is connected to a constant current drive circuit to detect the output voltage of each constant current drive circuit. A voltmeter is provided, and when all voltmeters become 0.7 V or more, the variable DC power supply 7
The adjustment of the power supply voltage Vcc may be completed. As a result, the power supply voltage Vcc can be adjusted to the lowest power supply voltage within a range in which all of the plurality of light emitting diodes driven by one variable DC power supply 7 can be normally lit.

<Embodiment 3> FIG. 5 is a block diagram showing a configuration of a light emitting diode driving circuit according to Embodiment 3 of the present invention. As shown in the figure, the light emitting diode drive circuit of the third embodiment is composed of a light emitting diode 1, a constant current drive circuit 2, a variable DC power supply with a signal control function 3, a current detection circuit 9, and a one-chip microcomputer 5. The external control device 6 is an external device that can be connected to the one-chip microcomputer 5 of the light emitting diode drive circuit of the third embodiment.

The current detection circuit 9 is provided between the cathode of the light emitting diode 1 and the output node N2 of the constant current drive circuit 2, and outputs a current detection signal S9 based on the current If.

FIG. 6 is an explanatory diagram showing an example of the internal configuration of the current detection circuit 9. As shown in the figure, the current-voltage conversion circuit 21 performs current-voltage conversion of the current If of the light emitting diode 1 with a resistor or the like and outputs a converted voltage V21 to the positive input of the comparator 23. The reference voltage VR is applied from the reference voltage generation circuit 22 to the negative input of the comparator 23. The reference voltage VR is set to a voltage equal to the converted voltage V21 when the current If is 0.1 A.

When the current If of the light emitting diode 1 is equal to or more than 0.1 A, the current detection circuit 9 having such a configuration outputs “H”.
(V21> VR), "L" (V21
<VR) The current detection signal S9 is output.

The one-chip microcomputer 5 performs the same operation as the one-chip microcomputer 5 of the first embodiment. The only difference is that a current detection signal S9 is used instead of the voltage detection signal S4. The other configuration is the same as that of the light emitting diode driving circuit of the first embodiment, and the description is omitted.

In such a configuration, the light emitting diode 1 has a threshold voltage Vf corresponding to a current If of 0.1 A.
A method of adjusting the power supply voltage Vcc of the variable DC power supply 3 with a signal control function when a light emitting diode having t of 2.05 V is provided will be described.

When a power control start signal S6 for instructing the start of control is sent from the external control device 6 to the one-chip microcomputer 5,
The one-chip microcomputer 5 is a variable DC power supply 3 with a signal control function.
, A power supply voltage control signal S5 instructing 0 V is output, and the power supply voltage Vcc output from the positive terminal of the variable DC power supply 3 with a signal control function is set to 0 V.

Then, based on the current detection signal S9, if the current detection signal S9 is "L", the one-chip microcomputer 5 controls the power supply voltage to instruct the power supply voltage to increase in predetermined steps, for example, in steps of 0.05V. The signal S5 is sent to the variable DC power supply 3 with a signal control function. Thereafter, similarly, the power supply voltage control signal S5 for instructing an increase in the power supply voltage is continuously output to the variable DC power supply with signal control function 3 until the current detection signal S9 changes from "L" to "H".

The power supply voltage Vcc rises in steps of 0.05 V. If the power supply voltage Vcc is 1.8 V or less, no current flows through the light emitting diode 1 and the current If maintains 0 A, so that the power supply voltage Vcc increases. Are all applied to the light emitting diode 1. At this time, since the current detection signal S9 is maintained at "L", the one-chip microcomputer 5 sends the power supply voltage control signal S5 instructing the variable DC power supply 3 with signal control function to increase the power supply voltage to the variable DC power supply 3 with signal control function. Then, the power supply voltage Vcc is further increased.

Thereafter, when the power supply voltage Vcc reaches 2.75 V, Vf = 2.05 V, Vob = 0.7 V, If
= 0.1 A, and the light emitting diode 1 normally lights up brightly. Here, the current detection signal S9 becomes "H" for the first time. In the one-chip microcomputer 5, the current detection signal S9 is "H".
Then, the transmission of the power supply voltage control signal S5 instructing the power supply voltage rise to the variable DC power supply with signal control function 3 is stopped,
The adjustment of the power supply voltage Vcc is completed. At this time, the power consumption Pc of the constant current drive circuit 2 is 0.07 W ｛Pc = 0.7 V ×
0.1 A = 0.07 W｝, and this constant current driving circuit 2
Can be suppressed to the lowest power consumption within a range where the device operates normally.

That is, by setting the power supply voltage Vcc when the current If = 0.1 A while changing the power supply voltage Vcc, low power consumption operation of the constant current drive circuit 2 is realized. Further, since the heat dissipation means can be omitted by saving the power of the constant current drive circuit 2, the size of the constant current drive circuit 2 can be reduced.

Even if the power supply voltage Vcc is increased to 2.75 V or more, the current If hardly increases due to the operation of the constant current drive circuit 2 as in the first embodiment.

The light emitting diode 1 shown in FIG.
When a light emitting diode whose threshold voltage Vft corresponding to f = 0.1 A is 2.2 V is used, the power supply voltage Vcc is adjusted to 2.9 V by performing the voltage adjustment by the power supply voltage control signal S5 of the one-chip microcomputer 5 described above. At this point, the light emitting diode 1 normally lights up, and the current detection signal S9 changes from "L" to "H". Therefore, the power supply voltage Vcc of the variable DC power supply 3 with a signal control function is set to 2.9V. You.

Also in this case, the power consumption P of the constant current drive circuit 2
c is the minimum 0.07W ｛Pc = 0.7V × 0.1A =
0.07 W}, and the power consumption can be suppressed to the minimum within a range in which the constant current drive circuit 2 operates normally.

When a plurality of light emitting diodes are connected in parallel to one variable DC power supply having a signal control function, a constant current drive circuit is connected to each cathode of the plurality of light emitting diodes to detect the current flowing through the light emitting diodes. A current detection circuit is provided, and when the current detection signals of all the current detection circuits become “H”, the adjustment of the power supply voltage of the variable DC power supply with a signal control function is completed. Thus, the power supply voltage Vcc can be adjusted to the lowest power supply voltage within a range in which all of the plurality of light emitting diodes driven by the single variable DC power supply with signal control function 3 can be normally lit.

<Embodiment 4> FIG. 7 is a block diagram showing a configuration of a light emitting diode driving circuit according to Embodiment 4 of the present invention. As shown in the figure, the light emitting diode drive circuit of the fourth embodiment includes a light emitting diode 1, a constant current drive circuit 2, a variable DC power supply 7, and an ammeter 10.

The ammeter 10 is provided between the cathode of the light emitting diode 1 and the constant current drive circuit 2, and can measure the current If flowing through the light emitting diode 1. FIG. 4 shows another configuration.
Since the second embodiment is the same as the second embodiment shown in FIG.

In such a configuration, as in the first embodiment, the variable DC power supply 7 in the case where a light emitting diode with a threshold voltage Vft of 2.05 V corresponding to a current If of 0.1 A is provided as the light emitting diode 1. A method of adjusting the power supply voltage Vcc will be described.

When the power supply voltage adjuster adjusts the variable resistor of the variable DC power supply 7 to gradually increase the power supply voltage Vcc from 0 V, when the power supply voltage Vcc reaches 2.75 V, Vf
= 2.05V, Vob = 0.7V, If = 0.1A, the ammeter 10 indicates 0.1A, and the light emitting diode normally lights up brightly. When the ammeter 10 indicates 0.1 A, the power supply voltage adjuster stops adjusting the variable DC power supply 7 and completes the adjustment of the power supply voltage. As a result, the power consumption can be suppressed to the minimum within a range where the constant current drive circuit 2 operates normally.

When the power supply voltage Vcc is further increased, the current If hardly increases due to the operation of the constant current drive circuit 2 as in the first embodiment, and almost all the rise of the power supply voltage Vcc is a constant current. The output voltage Vob of the drive circuit 2 corresponds to a rise.

The light emitting diode 1 shown in FIG.
When a light emitting diode whose threshold voltage Vft corresponding to f = 0.1 A is 2.2 V is used, the light emitting diode normally lights up when the power supply voltage Vcc is increased to 2.9 V, as in Embodiment 1. The ammeter 10 indicates 0.1 A. When the ammeter 10 indicates 0.1 A, the power supply voltage adjuster stops adjusting the variable DC power supply 7 and completes the adjustment of the power supply voltage.
As a result, the power consumption can be suppressed to the minimum within a range where the constant current drive circuit 2 operates normally.

When a plurality of light emitting diodes are connected in parallel to one variable DC power supply, a constant current drive circuit is connected to the cathode of each of the plurality of light emitting diodes, and an ammeter is used to detect the current flowing through each light emitting diode. The adjustment of the power supply voltage Vcc of the variable DC power supply 7 may be completed when all the ammeters have reached 0.1 A or more. As a result, the power supply voltage Vcc can be adjusted to the lowest power supply voltage within a range in which all of the plurality of light emitting diodes driven by one variable DC power supply 7 can be normally lit.

<Fifth Embodiment> FIG. 8 is a block diagram showing a configuration of a light emitting diode driving circuit according to a fifth embodiment of the present invention. As shown in the figure, the driving circuit of the light emitting diode according to the fifth embodiment includes a light emitting diode 1, a constant current driving circuit 2, a variable DC power supply 3 having a signal control function, a voltage detecting circuit 4, an optical-electrical converting circuit 11, Chip microcomputer 5
The external control device 6 is an external device that can be connected to the one-chip microcomputer 5 of the light emitting diode drive circuit of the fifth embodiment.

The photoelectric conversion circuit 11 is composed of a photoelectric conversion element used for a solar cell or the like and an amplifier circuit such as an operational amplifier. The photoelectric conversion circuit 11 outputs a converted voltage V11 proportional to the light emission luminance of the light emitting diode 1 to the voltage detection circuit 4. I do. For example, when the light emission luminance L = 0.2 cd / m ² , the conversion voltage V1
1 is 0.09 V, and when the light emission luminance L = 2 cd / m ² , the conversion voltage V11 is 0.7 V.

FIG. 9 shows a current If flowing through the light emitting diode 1.
6 is a graph showing the relationship between the luminance and the light emission luminance L. As shown in the figure, there is a proportional relationship between the current If and the light emission luminance L. For example, if If = 0.01 A, L = 0.2 cd / m ² , If
At 0.10 A, it becomes 2.0 cd / m ² . Therefore,
If the light emission luminance L is 2.0 cd / m ² or more, the light emitting diode 1 is normally lit.

The voltage detection circuit 4 has a conversion voltage V11 of the photoelectric conversion circuit 11 of 0.7 V or more (light emission luminance L = 2 cd /
if to m ² or more) "H", if less than 0.7V "L"
Is output. That is, the voltage detection signal S4 of the fifth embodiment functions as a luminance detection signal indicating whether or not the light emission luminance L of the light emitting diode 1 is equal to or higher than the reference luminance (2.0 cd / m ² ). Note that the other configuration is the same as the configuration of the first embodiment shown in FIG.

In such a configuration, the light emitting diode 1 has a threshold voltage Vf corresponding to a current If of 0.1 A.
A method of adjusting the power supply voltage Vcc of the variable DC power supply 3 with a signal control function when a light emitting diode having t of 2.05 V is provided will be described.

When a power control start signal S6 for instructing the start of control is sent from the external control device 6 to the one-chip microcomputer 5,
The one-chip microcomputer 5 is a variable DC power supply 3 with a signal control function.
, A power supply voltage control signal S5 instructing 0 V is output, and the power supply voltage Vcc output from the positive terminal of the variable DC power supply 3 with a signal control function is set to 0 V.

Then, based on the voltage detection signal S4, if the voltage detection signal S4 is "L", the one-chip microcomputer 5 controls the power supply voltage instructing to increase the power supply voltage in predetermined steps, for example, in steps of 0.05V. The signal S5 is sent to the variable DC power supply 3 with a signal control function. Thereafter, similarly, the power supply voltage control signal S5 for instructing the increase of the power supply voltage is continuously output to the variable DC power supply with signal control function 3 until the voltage detection signal S4 changes from "L" to "H".

Thereafter, when the power supply voltage Vcc reaches 2.75 V, Vf = 2.05 V, Vob = 0.7 V, If
= 0.1 A, L = 2.0 cd / m ² , and the light emitting diode 1 normally lights up brightly. Here, the voltage detection signal S4 becomes "H" for the first time. When the voltage detection signal S4 becomes "H", the one-chip microcomputer 5 stops sending the power supply voltage control signal S5 instructing the power supply voltage increase to the variable DC power supply with signal control function 3, and completes the adjustment of the power supply voltage Vcc. . The power consumption Pc of the constant current drive circuit 2 at this time is 0.0
7 W {Pc = 0.7 V × 0.1 A = 0.07 W}, and the power consumption can be suppressed to the minimum within a range where the constant current drive circuit 2 operates normally.

That is, the power supply voltage Vcc when the light emission luminance L becomes 2.0 cd / m ² while changing the power supply voltage Vcc
, Low power consumption operation of the constant current drive circuit 2 is realized. Further, since the heat dissipation means can be omitted by saving the power of the constant current drive circuit 2, the size of the constant current drive circuit 2 can be reduced.

Even if the power supply voltage Vcc is increased to 2.75 V or more, the current If hardly increases due to the operation of the constant current drive circuit 2, and the rise of the power supply voltage Vcc is almost entirely reduced by the constant current drive circuit 2. It becomes the rising voltage of the output voltage Vob.

The light emitting diode 1 shown in FIG.
When a light emitting diode whose threshold voltage Vft corresponding to f = 0.1 A is 2.2 V is used, the power supply voltage Vcc is adjusted to 2.9 V by performing the voltage adjustment by the power supply voltage control signal S5 of the one-chip microcomputer 5 described above. At this point, the light emitting diode 1 normally lights up, and the voltage detection signal S4 changes from "L" to "H". Therefore, the power supply voltage Vcc of the variable DC power supply 3 with a signal control function is set to 2.9V. You. At this time, Vf = 2.2 V, Vob = 0.7 V, If = 0.
1A, L = 2.0 cd / m ² .

Also in this case, the power consumption P of the constant current drive circuit 2
c is the minimum 0.07W ｛Pc = 0.7V × 0.1A =
0.07 W}, and the power consumption can be suppressed to the minimum within a range in which the constant current drive circuit 2 operates normally.

When a plurality of light-emitting diodes are connected in parallel to one variable DC power supply with a signal control function, a constant current drive circuit is connected to each of the plurality of light-emitting diodes' cathodes to detect the luminance of each light-emitting diode. Is provided with an optical-electrical conversion circuit and a voltage detection circuit, and when the voltage detection signals of all the voltage detection circuits become “H”, the adjustment of the power supply voltage of the variable DC power supply with a signal control function is completed. Thereby, the power supply voltage Vcc can be adjusted to the lowest power supply voltage within a range in which all of the plurality of light emitting diodes driven by one variable DC power supply 3 having the signal control function can be turned on.

<Sixth Embodiment> FIG. 10 is a block diagram showing a configuration of a light emitting diode driving circuit according to a sixth embodiment of the present invention. As shown in the figure, the light emitting diode drive circuit of the sixth embodiment includes a light emitting diode 1, a constant current drive circuit 2, a variable DC power supply 7, and a luminance meter 12.

The luminance meter 12 can measure the light emission luminance of the light emitting diode 1. The other configuration is the same as the configuration of the second embodiment shown in FIG.

In such a configuration, as in the first embodiment, a variable DC power supply 7 having a threshold voltage Vft of 2.05 V corresponding to a current If of 0.1 A is provided as light emitting diode 1. A method of adjusting the power supply voltage Vcc will be described.

When the power supply voltage adjuster adjusts the variable resistor of the variable DC power supply 7 to gradually increase the power supply voltage Vcc from 0 V, when the power supply voltage Vcc reaches 2.75 V, Vf
= 2.05 V, Vob = 0.7 V, If = 0.1 A, the luminance meter 12 indicates 2.0 cd / m ² , and the light emitting diode normally lights up brightly. This luminance meter 12 is 2.0
When cd / m ² (reference luminance) is indicated, the power supply voltage adjuster stops adjusting the variable DC power supply 7 and completes the adjustment of the power supply voltage. As a result, the power consumption can be suppressed to the minimum within a range where the constant current drive circuit 2 operates normally.

When the power supply voltage Vcc is further increased, the current If hardly increases due to the operation of the constant current drive circuit 2 as in the first embodiment, and almost all the rise of the power supply voltage Vcc is a constant current. The output voltage Vob of the drive circuit 2 corresponds to a rise.

Further, as the light emitting diode 1 of FIG.
When a light emitting diode whose threshold voltage Vft corresponding to If = 0.1 A is 2.2 V is used, the light emitting diode normally lights up when the power supply voltage Vcc is increased to 2.9 V, as in the second embodiment. The luminance meter 12 indicates 2.0 cd / m ² . When the luminance meter 12 indicates 2.0 cd / m ² , the power supply voltage adjuster stops adjusting the variable DC power supply 7 and completes the adjustment of the power supply voltage. As a result, the power consumption can be suppressed to the minimum within a range where the constant current drive circuit 2 operates normally.

When a plurality of light emitting diodes are connected in parallel to one variable DC power supply, a constant current drive circuit is connected to the cathode of each of the plurality of light emitting diodes, and a luminance meter for detecting the light emission luminance of each light emitting diode. The adjustment of the power supply voltage Vcc of the variable DC power supply 7 may be completed when all the luminance meters become 2.0 cd / m ² or more. As a result, the power supply voltage Vcc can be adjusted to the lowest power supply voltage within a range in which all of the plurality of light emitting diodes driven by one variable DC power supply 7 can be normally lit.

<Seventh Embodiment> FIG. 11 is a block diagram showing a configuration of a light emitting diode driving circuit according to a seventh embodiment of the present invention. As shown in the figure, the light emitting diode drive circuit of the seventh embodiment has five light emitting diodes 1a.
1e, five constant current drive circuits 2a to 2e, a variable DC power supply 3 with a signal control function, a current detection circuit 9, and a one-chip microcomputer 5. The external control device 6 is a light emitting diode according to the seventh embodiment. Is an external device that can be connected to the one-chip microcomputer 5 of the drive circuit.

The anodes of the five light emitting diodes 1a to 1e are connected to the positive terminal (+) of the variable DC power supply with signal control function 3 via the current detecting circuit 19 to receive the power supply voltage Vcc. Each of the cathodes 1a to 1e is connected to a corresponding one of the constant current driving circuits 2a to 2e. The constant current drive circuits 2a to 2e perform a constant current supply operation to each of the light emitting diodes 1a to 1e based on the output voltage Vob which is the cathode voltage of the light emitting diodes 1a to 1e.

The current detection circuit 19 includes the light emitting diodes 1a to 1a.
The current detection signal S19 is provided between the anode of the variable DC power supply 1e and the positive terminal side of the variable DC power supply 3 with a signal control function, and outputs a current detection signal S19 based on a total current TIf that is a total current flowing through the light emitting diodes 1a to 1e.

The current detection circuit 19 calculates the total current TIf
Is higher than 0.5A, the current detection signal S19 of "H" is output if it is 0.5A or lower, and "L" is output if it is 0.5A or lower. That is, if the total current TIf is 0.5 A, the light emitting diode 1
It is determined that all of a to 1e emit light normally. Other configurations are the same as those of the light emitting diode driving circuit of the first embodiment shown in FIG.

In such a configuration, as the light emitting diodes 1a to 1e of FIG. 11, light emitting diodes whose current If varies with a threshold voltage Vft corresponding to 0.1 A in a range of 1.9V to 2.1V are provided. The method of adjusting the power supply voltage Vcc of the variable DC power supply 3 with a signal control function in the case where the power supply voltage Vcc is adjusted will be described.

When a power control start signal S6 for instructing the start of control is sent from the external control device 6 to the one-chip microcomputer 5,
The one-chip microcomputer 5 is a variable DC power supply 3 with a signal control function.
, A power supply voltage control signal S5 instructing 0 V is output, and the power supply voltage Vcc output from the positive terminal of the variable DC power supply 3 with a signal control function is set to 0 V.

If the current detection signal S19 is "L" based on the current detection signal S19, the one-chip microcomputer 5 controls the power supply voltage to instruct the power supply voltage to be increased in predetermined steps, for example, in steps of 0.05V. The signal S5 is sent to the variable DC power supply 3 with a signal control function. Thereafter, similarly, the power supply voltage control signal S5 for instructing the increase in the power supply voltage is continuously output to the variable DC power supply with signal control function 3 until the current detection signal S19 changes from "L" to "H".

The power supply voltage Vcc increases in steps of 0.05 V. If the power supply voltage Vcc is 1.8 V or less, no current flows through the light emitting diode 1 and the current If maintains 0 A, so that the power supply voltage Vcc increases. Are all applied to the light emitting diode 1. At this time, since the current detection signal S19 maintains “L”, the one-chip microcomputer 5 sends the power supply voltage control signal S5 instructing the variable DC power supply 3 with a signal control function to increase the power supply voltage to the variable DC power supply 3 with a signal control function. Then, the power supply voltage Vcc is further increased.

For example, when the power supply voltage Vcc is 2.05 V, the variation of the light emitting diodes 1a to 1e is Vf = 1.85.
-2.05V, Vob = 0-0.2V, If = 0-0.
05A, and the total current TIf is at most 0.07
There is about A.

Therefore, since the voltage detection signal S4 is still "L", the one-chip microcomputer 5 sends the one-chip microcomputer 5 for instructing the variable DC power supply 3 with a signal control function to increase the power supply voltage. The power supply voltage Vcc of the variable DC power supply 3 is increased.

Thereafter, when the power supply voltage Vcc reaches 2.75 V, the current If of the light emitting diodes 1a to 1e is
The light emitting diode whose threshold voltage Vft corresponding to = 0.1 A is 2.05 V or less normally lights up brightly, and the total current TIf is about 0.45 A.

Therefore, since the voltage detection signal S4 is still "L", the one-chip microcomputer 5 sends the one-chip microcomputer 5 instructing the variable DC power supply 3 with a signal control function to increase the power supply voltage. The power supply voltage Vcc of the variable DC power supply 3 is increased.

Thereafter, when the power supply voltage Vcc reaches 2.80 V, the threshold voltage Vf corresponding to the current If = 0.1 A is applied.
All of the light emitting diodes 1a to 1e whose t is 2.1 V or less normally light up brightly, and the total current TIf is 0.1.
Reaches 5A.

Here, the current detection signal S19 becomes "H" for the first time. The one-chip microcomputer 5 receives the current detection signal S
When “19” becomes “H”, the variable DC power supply with signal control function 3
To stop supplying the power supply voltage control signal S5 for instructing the power supply voltage rise to complete the adjustment of the power supply voltage Vcc. At this time, the power consumption Pc of each of the constant current drive circuits 2a to 2e is 0.075W ｛Pc = 0.75V × 0.1A = 0.07
5W}, and the power consumption can be suppressed to the minimum within a range where all the constant current drive circuits 2a to 2e operate normally.

Even if power supply voltage Vcc is increased to 2.80 V or more, constant current drive circuit 2a
The current If hardly increases due to the action of ~ 2e.

In FIG. 11, the current detecting circuit 19
Is replaced by an ammeter, the variable DC power supply with signal control function 3 is replaced by a variable DC power supply 7, and the one-chip microcomputer 5 and the external control device 6 are omitted. When it becomes 5A or more,
It is also conceivable to obtain a light emitting diode drive circuit having a configuration capable of completing the adjustment of the power supply voltage Vcc of the variable DC power supply 7.

<Eighth Embodiment> FIG. 12 is a block diagram showing a configuration of a light emitting diode drive circuit according to an eighth embodiment of the present invention. As shown in the figure, the light emitting diode driving circuit of the eighth embodiment has five light emitting diodes 1a.
1e, five constant current drive circuits 2a to 2e, and a variable DC power supply 7.

The five light emitting diodes 1a to 1e are connected to the positive terminals of the respective variable anode DC power supplies 7 to receive the power supply voltage Vcc, and the respective cathodes are connected to the constant current driving circuits 2a to 2e.
2e is connected to the corresponding constant current drive circuit. The constant current driving circuits 2a to 2e are light emitting diodes 1a to 1 respectively.
The constant current supply operation to each of the light emitting diodes 1a to 1e is performed based on the output voltage Vob which is the cathode voltage of e. The variable DC power supply 7 is the same as in the second embodiment.

In such a configuration, when the light emitting diodes 1a to 1e are provided, the threshold voltage Vft corresponding to the current If of 0.1 A varies in the range of 1.9V to 2.1V. A method of adjusting the power supply voltage Vcc of the variable DC power supply 7 will be described.

First, the threshold voltage Vft corresponding to the current If = 0.1 A of each of the light emitting diodes 1a to 1e is measured in advance using an external device. Then, among the light emitting diodes 1a to 1e, the lowest power supply voltage V in a range where the light emitting diode having the maximum threshold voltage Vft normally lights up.
Adjust the variable DC power supply 7 to cc.

In this case, since the threshold voltage Vft = 2.1 V is the maximum, the constant current drive circuit 2 outputs the current If = 0.1 A
0.7V which is the output voltage Vob when supplying
The variable DC power supply 7 is adjusted so that the power supply voltage Vcc becomes 2.8 V (= 2.1 + 0.7).

When the power supply voltage Vcc is set to 2.80 V,
All of the light emitting diodes 1a to 1e whose threshold voltage Vft at the current If = 0.1 A is 2.1 V or less normally light up brightly. At this time, the power consumption Pc of each of the constant current drive circuits 2a to 2e is 0.075W ｛Pc = 0.75V ×
0.1A = 0.075 W｝, and the power consumption can be suppressed to the minimum within a range where all the constant current drive circuits 2a to 2e operate normally.

It is to be noted that, instead of measuring the threshold voltage Vft corresponding to the current If = 0.1 A of each of the light emitting diodes 1a to 1e, the measured values of the light emitting diodes 1a to 1e at the time of shipment inspection are used. 1a ~
The work of measuring the threshold voltage Vft of 1e can be omitted.

In the eighth embodiment, the case where the number of light emitting diodes is plural (five) is described as an example. In this case, the threshold voltage Vft corresponding to the current If = 0.1 A of the light emitting diode is measured in advance by using an external device or by using the measured value at the time of shipping inspection, and the light emitting diode is normally turned on. The variable DC power supply 7 may be adjusted to the lowest power supply voltage Vcc within the range.

[0129]

As described above, in the light emitting diode driving circuit according to the first aspect of the present invention, the variable power supply for supplying the power supply voltage for light emission of the light emitting diode to the anode of the light emitting diode has a variable power supply voltage. Since it is possible, by setting the power supply voltage to the lowest level at which the light emitting diode normally emits light, the low power consumption operation in which the output voltage of the constant current driving means defined by the power supply voltage is minimized. Making it possible.

According to a second aspect of the present invention, the light emitting diode driving circuit includes a light emitting diode characteristic value detecting means capable of detecting a light emitting diode characteristic value serving as an index indicating whether the light emitting diode emits light normally. Based on the light emitting diode characteristic value, the power supply voltage at the lowest level at which the light emitting diode normally emits light can be relatively easily detected.

According to a third aspect of the present invention, the power supply voltage adjusting means of the light emitting diode driving circuit includes a light emitting diode normally emitting light based on a light emitting diode characteristic value obtained while changing the power supply voltage during the power supply voltage adjusting process. In order to finally set the power supply voltage at the lowest level, the power supply voltage adjusting means executes the power supply voltage adjustment processing, so that the power supply voltage can be automatically adjusted to a power supply voltage that can operate normally with low power consumption.

According to a fourth aspect of the present invention, in the light emitting diode driving circuit, by setting the power supply voltage at the lowest level at which the plurality of light emitting diodes can emit light normally, a low power consumption operation in which the output voltage is minimized. Is possible.

The light emitting diode driving circuit according to claim 5 includes a plurality of light emitting diode characteristic value detecting means capable of detecting a plurality of light emitting diode characteristic values indicating whether or not the plurality of light emitting diodes emit light normally. Therefore, based on the plurality of light emitting diode characteristic values, it is possible to relatively easily detect the lowest power supply voltage at a level at which all of the plurality of light emitting diodes normally emit light.

According to a sixth aspect of the present invention, in the light emitting diode driving circuit, a range in which all of the plurality of light emitting diodes emit light normally based on the plurality of light emitting diode characteristic values obtained while changing the power supply voltage during the power supply voltage adjusting process. Power supply voltage adjusting means for finally setting the lowest level of power supply voltage, the power supply voltage adjusting means executes the power supply voltage adjustment processing, thereby automatically reducing the power supply voltage to a power supply voltage capable of normal operation with low power consumption. Can be adjusted.

According to a seventh aspect of the present invention, the voltage detecting means of the light emitting diode driving circuit comprises:
That is, since the output voltage of the constant current driving means can be detected, the comparison result between the output voltage and the predetermined voltage (the lowest level voltage at which a constant current flows through the light emitting diode) is verified while changing the power supply voltage. The power supply voltage at the lowest level at which the light emitting diode normally emits light can be relatively easily detected.

The power supply voltage adjusting means of the light emitting diode driving circuit according to claim 8, wherein the power supply when the cathode voltage becomes equal to a predetermined voltage based on the voltage detection signal while changing the power supply voltage during the power supply voltage adjustment processing. In order to set the power supply voltage, the power supply voltage adjustment unit can execute the power supply voltage adjustment processing, so that the power supply voltage can be automatically adjusted to a power supply voltage that can operate normally with low power consumption.

Since the current detecting means according to the ninth aspect can detect the current flowing through the light emitting diode, it is possible to verify whether or not the current is at a level at which the light emitting diode normally emits light while changing the power supply voltage. In addition, the power supply voltage at the lowest level at which the light emitting diode normally emits light can be detected relatively easily.

According to a tenth aspect of the present invention, in the power supply voltage adjusting means of the light emitting diode driving circuit, the current flowing through the light emitting diode becomes equal to a predetermined current based on the current detection signal while changing the power supply voltage during the power supply voltage adjusting process. In order to set the power supply voltage at the time, the power supply voltage adjusting means executes the power supply voltage adjustment processing, so that the power supply voltage can be automatically adjusted to a power supply voltage which can operate normally with low power consumption.

Since the luminance detecting means of the light emitting diode driving circuit according to the eleventh aspect can detect the light emitting luminance of the light emitting diode, the luminance detecting means compares the light emitting luminance with the normal level reference luminance while changing the power supply voltage. By performing the verification, it is possible to relatively easily detect the power supply voltage at the lowest level at which the light emitting diode normally emits light.

According to a twelfth aspect of the present invention, in the power supply voltage adjusting means of the light emitting diode driving circuit, the power supply voltage when the emission luminance becomes equal to the reference luminance based on the luminance detection signal while changing the power supply voltage during the power supply voltage adjustment processing. To set
By causing the power supply voltage adjusting means to execute the power supply voltage adjustment processing, the power supply voltage can be automatically adjusted to a power supply voltage capable of operating normally with low power consumption.

According to a thirteenth aspect of the present invention, in the power supply voltage adjusting means of the light emitting diode driving circuit, the total value of the current flowing through the light emitting diode is a predetermined total value based on the current detection signal while changing the power supply voltage during the power supply voltage adjusting process. In order to set the power supply voltage when it becomes equal to the reference value, the power supply voltage adjusting means can execute the power supply voltage adjustment processing to set the power supply voltage to the lowest level in a range where all of the plurality of light emitting diodes can normally emit light, As a result, the power supply voltage can be automatically adjusted to a power supply voltage that allows normal operation with low power consumption.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a light emitting diode drive circuit according to Embodiment 1 of the present invention.

FIG. 2 is a graph showing current-voltage characteristics of a light emitting diode.

FIG. 3 is a graph showing a constant current supply characteristic of a constant current drive circuit.

FIG. 4 is a block diagram illustrating a configuration of a light emitting diode drive circuit according to Embodiment 2.

FIG. 5 is a block diagram illustrating a configuration of a light emitting diode drive circuit according to Embodiment 3.

6 is an explanatory diagram showing an internal configuration of the current detection circuit of FIG.

FIG. 7 is a block diagram illustrating a configuration of a light emitting diode driving circuit according to a fourth embodiment.

FIG. 8 is a block diagram illustrating a configuration of a light emitting diode drive circuit according to a fifth embodiment.

FIG. 9 is a graph showing current-luminance characteristics of a light emitting diode.

FIG. 10 is a block diagram illustrating a configuration of a light emitting diode drive circuit according to Embodiment 6.

FIG. 11 is a block diagram illustrating a configuration of a light emitting diode drive circuit according to Embodiment 7.

FIG. 12 is a block diagram illustrating a configuration of a light emitting diode drive circuit according to an eighth embodiment.

FIG. 13 is a block diagram showing a configuration of a conventional light emitting diode drive circuit.

FIG. 14 is a block diagram schematically showing the circuit of FIG.

[Explanation of symbols]

1, 1a-1e light emitting diode, 2, 2a-2e constant current drive circuit, 3 variable DC power supply with signal control function, 4
Voltage detection circuit, 5 one-chip microcomputer, 7 variable DC power supply, 8 voltmeter, 9, 19 current detection circuit, 10 ammeter, 11 opto-electric conversion circuit, 12 luminance meter.

Claims (13)

[Claims] 1. A light emitting diode, a power supply voltage for light emission of the light emitting diode is supplied to an anode of the light emitting diode, and a variable power supply capable of variably setting the power supply voltage; and a cathode connected to the light emitting diode, A constant current driving means for supplying a constant current to the light emitting diode when the voltage at the cathode becomes an output voltage and the output voltage is equal to or higher than a predetermined voltage. 2. The light-emitting diode driving circuit according to claim 1, further comprising a light-emitting diode characteristic value detecting means capable of detecting a light-emitting diode characteristic value serving as an index indicating whether the light-emitting diode emits light normally. . 3. A power supply voltage adjusting process, wherein the power supply voltage is changed while the light emitting diode characteristic value obtained by measurement by the light emitting diode characteristic value detection means is based on:
3. The light emitting diode driving circuit according to claim 2, further comprising a power supply voltage adjusting unit that finally sets the power supply voltage at the lowest level in a range where the light emitting diode normally emits light. 4. The light emitting diode according to claim 1, wherein the light emitting diode includes a plurality of light emitting diodes, and the constant current driving unit includes a plurality of constant current driving units corresponding to the plurality of light emitting diodes on a one-to-one basis. Drive circuit. 5. A light emitting diode which is provided in a one-to-one correspondence with each of the plurality of light emitting diodes and serves as an index indicating whether or not a corresponding light emitting diode among the plurality of light emitting diodes normally emits light. 5. The light emitting diode driving circuit according to claim 4, further comprising a plurality of light emitting diode characteristic value detecting means capable of detecting characteristic values. 6. In the power supply voltage adjustment process, all of the plurality of light emitting diodes are changed based on the plurality of light emitting diode characteristic values obtained by measuring the plurality of light emitting diode characteristic value detecting means while changing the power supply voltage. 6. The light emitting diode driving circuit according to claim 5, further comprising a power supply voltage adjusting means for finally setting the power supply voltage at the lowest level within a range in which light emission is normal. 7. The light emitting diode characteristic value detecting means,
Including voltage detection means capable of detecting the voltage of the cathode of the light emitting diode as the light emitting diode characteristic value,
A driving circuit for a light emitting diode according to claim 2. 8. The light-emitting diode includes a light-emitting diode that emits light normally when the constant current flows, and the light-emitting diode characteristic value detecting means calculates a comparison result between the voltage of the cathode of the light-emitting diode and the predetermined voltage. The power supply voltage adjustment unit includes a voltage detection unit that outputs a voltage detection signal, the light emitting diode characteristic value includes the voltage detection signal,
4. The light emitting diode driving circuit according to claim 3, further comprising: means for setting the power supply voltage when the voltage of the cathode becomes equal to the predetermined voltage, based on the voltage detection signal obtained while changing the power supply voltage. 9. The light emitting diode characteristic value detecting means,
3. A light emitting device according to claim 2, further comprising a current detecting means for detecting a current flowing through the light emitting diode as the light emitting diode characteristic value.
The driving circuit of the light-emitting diode according to the above. 10. The light-emitting diode includes a light-emitting diode that emits light normally when a predetermined current flows, and the light-emitting diode characteristic value detecting means determines a comparison result between the current flowing through the light-emitting diode and the predetermined current. The power supply voltage adjustment unit includes a current detection unit that outputs the detection signal, and the light emitting diode characteristic value includes the current detection signal.
Based on the current detection signal while changing the power supply voltage, including means for setting the power supply voltage when the current flowing through the light emitting diode becomes equal to the predetermined current,
A light emitting diode driving circuit according to claim 3. 11. The light emitting diode driving circuit according to claim 2, wherein said light emitting diode characteristic value detecting means includes a luminance detecting means capable of detecting a light emitting luminance of said light emitting diode as said light emitting diode characteristic value. 12. The light emitting diode characteristic value detecting means includes a luminance detecting means for outputting, as a luminance detecting signal, a comparison result between the light emitting luminance of the light emitting diode and a reference luminance of a level at which the light emitting diode emits light normally. The light emitting diode characteristic value includes the luminance detection signal, the power supply voltage adjustment means, during the power supply voltage adjustment processing,
4. The light emitting diode driving circuit according to claim 3, further comprising: a unit that sets the power supply voltage when the light emission luminance becomes equal to the reference luminance based on the luminance detection signal while changing the power supply voltage. 13. Current detection means for outputting, as a current detection signal, a comparison result between a total value of currents flowing through the plurality of light emitting diodes and a total reference value determined to be normal for the plurality of light emitting diodes to emit light; Power supply voltage adjusting means for setting the power supply voltage at the time when the total value of the current flowing through the light emitting diode becomes equal to a predetermined total reference value based on the current detection signal while changing the power supply voltage during the power supply voltage adjustment process The driving circuit for a light emitting diode according to claim 4, further comprising: