JP2009016460A - Driving device and illuminating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device and an illuminating device which reduces a power loss in a constant current element for supplying a specified current to LEDs. <P>SOLUTION: In the driving device, one end of each of resistance elements R1, R2, R3, and R4 is connected to a cathode of each of LEDs 1-4, and the other end of each of resistance elements R1, R2, R3, and R4 is connected with a microcomputer 50. The microcomputer 50 detects voltage of the cathode of each of the LEDs 1-4 by means of the resistance elements R1-R4. The microcomputer 50 also controls a regulator 20 depending on a difference between a detected voltage and a specified threshold, and reduces voltage Vdd. Thus, emitter-collector voltage of a transistor Q1 is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a driving device that supplies current to an LED and an illumination device including the driving device.

  Conventionally, fluorescent lamps, incandescent lamps, and the like are used as light sources in lighting devices and display devices. On the other hand, technical development for using an LED (light emitting diode) having features of a long life and low power consumption as compared with a conventional light source as a light source for illumination or display has been performed.

When such an LED is used in a lighting device or the like, in order to ensure sufficient brightness, a large number of LEDs are connected in series or in parallel and arranged in the device as an aggregate of LEDs. Moreover, in order to make the brightness of each LED uniform, an LED driving device including a constant current element that makes a current flowing through each LED constant is disclosed (see Patent Document 1).
JP 2007-42758 A

  However, in the LED driving device as in Patent Document 1, for example, a transistor is used as the constant current element, and a total current of currents flowing through the LEDs connected in parallel flows through such a transistor. For this reason, the power loss caused by the voltage applied between the emitter and collector of the transistor and the current flowing through the collector increases, and it becomes a problem how to dissipate the heat generated by the transistor. In particular, when the heat generation of the transistor is large, the lifetime of the transistor may be deteriorated and the reliability of the device may be impaired.

  The present invention has been made in view of such circumstances, and provides a driving device that can reduce power loss caused by a constant current element that supplies a predetermined current to an LED, and an illumination device including the driving device. With the goal.

  The drive device according to the present invention is characterized in that a power loss generated in a constant current element that supplies a predetermined current to a load such as an LED can be reduced.

  The drive device according to the present invention is a drive device including a constant current element for supplying a predetermined current to a load such as an LED, and the voltage supplied to the load is variable, and is applied to the constant current element. A voltage detection unit that detects a voltage to be detected, a comparison unit that compares the voltage detected by the voltage detection unit with a predetermined threshold, and a voltage supplied to the load is changed based on the comparison result of the comparison unit And a control unit that controls the voltage applied to the constant current element to be low.

  In the driving device according to the present invention, the constant current element is a transistor and is connected in series to the load, and the voltage detection unit is either an anode or a cathode of the load, or a collector or an emitter of the transistor. It is configured to detect such a voltage.

  In the driving apparatus according to the present invention, the voltage supply unit is configured to divide the voltage supplied to the load by a circuit in which a plurality of series circuits of resistance elements having different resistance values and switching elements are connected in parallel. The control unit is configured to control one of the switching elements to be turned on based on a result of comparison by the comparison unit.

  In the driving device according to the present invention, the voltage supply unit is configured to divide a voltage supplied to the load by a circuit in which a plurality of series circuits of a resistance element and a switching element are connected in parallel, and the control unit Is configured to control the number of switching elements to be turned on based on the result of comparison by the comparison unit.

  The illumination device according to the present invention includes the drive device according to any one of the above-described inventions.

  In the present invention, power loss caused by a constant current element that supplies a predetermined current to a load such as an LED is reduced.

  In the present invention, the voltage applied to the constant current element is detected by the voltage detection unit, and the comparison unit compares the detected voltage with a predetermined threshold value. A control part changes the voltage supplied to LED (load) based on the comparison result, and makes the voltage applied to a constant current element low. For example, when the voltage detected by the voltage detector is high, it is considered that the power loss consumed by the constant current element is large, so the voltage applied to the constant current element is lowered. Thereby, the power loss which arises with a constant current element can be made small, and heat_generation | fever of a constant current element can be suppressed. Further, heat generation can be prevented and reliability can be improved. Further, it is not necessary to take a heat dissipation measure such as providing a heat dissipation member for the constant current element.

  In the present invention, the voltage detection unit detects the voltage of the anode or cathode of the LED or the collector or emitter of the transistor in the series circuit of the LED and the transistor. Since the forward voltage of the LED when a predetermined current flows through the LED can be grasped in advance, the magnitude of the voltage between the emitter and collector of the transistor can be determined, for example, by connecting the LED collector and the collector of the transistor. In this case, it is proportional to the magnitude of each voltage of the anode or cathode of the LED or the collector (when NPN type) or emitter (when PNP type) of the transistor. As a result, the voltage between the emitter and collector of the transistor as the constant current element can be detected, and power loss generated in the transistor can be reduced to suppress heat generation.

  In the present invention, the voltage supplied to the LED is divided by a circuit in which a plurality of series circuits of resistance elements and switching elements having different resistance values are connected in parallel, and the control unit determines the comparison result in the comparison unit. Based on this, control is performed to turn on any of the switching elements. For example, when the voltage applied to the constant current element is high, the voltage supplied to the LED is lowered by turning on the switching element connected to the resistance element having a small resistance value. Thereby, the voltage applied to the constant current element is lowered. When the voltage applied to the constant current element is higher, the voltage supplied to the LED is further lowered by turning on the switching element connected to the resistance element having a smaller resistance value. Thereby, the voltage applied to the constant current element is further lowered. Thereby, power loss generated in the transistor can be reduced and heat generation can be suppressed.

  In the present invention, the voltage supplied to the LED is divided by a circuit in which a plurality of series circuits of resistance elements and switching elements are connected in parallel, and the control unit is turned on based on the comparison result in the comparison unit. Control the number of switching elements to be used. For example, when the voltage applied to the constant current element is high, the voltage supplied to the LED is increased by increasing the number of switching elements that are turned on and increasing the number of resistance elements connected in parallel to lower the resistance value. Lower. Thereby, the voltage applied to the constant current element is lowered. Further, when the voltage applied to the constant current element is higher, the number of switching elements to be turned on is further increased, and the resistance value is further decreased by further increasing the number of resistance elements connected in parallel, thereby reducing the LED. The voltage supplied to is further reduced. Thereby, the voltage applied to the constant current element is further lowered. Thereby, power loss generated in the transistor can be reduced and heat generation can be suppressed.

  According to the present invention, it is possible to provide a lighting device that can reduce power loss caused by a constant current element that supplies a predetermined current to an LED, can prevent heat generation, and can improve reliability.

  In the present invention, it is possible to reduce power loss generated in the constant current element and to suppress heat generation of the constant current element. Further, heat generation can be prevented and reliability can be improved. Further, it is not necessary to take a heat dissipation measure such as providing a heat dissipation member for the constant current element.

  Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof. FIG. 1 is a circuit diagram showing a main configuration of a driving apparatus 100 according to the present invention. The driving device 100 supplies a predetermined voltage Vdd to the LEDs 1, 2, 3, and 4 mounted on a substrate (not shown) and supplies a predetermined constant current to the entire LEDs 1, 2, 3, and 4 connected in parallel. To do. In addition, the board | substrate which mounted the drive device 100 and LED1-4 can also be comprised as a separate component, or the electronic component which comprises the drive apparatus 100 can also be mounted in the board | substrate which mounted LED1-4. Each of the LEDs 1 to 4 has a plurality of LED chips connected in series and / or in parallel. The number of LEDs is an example, and is not limited to four.

  The cathodes of the LEDs 1 to 4 are connected to the anodes of diodes D1, D2, D3, and D4 as rectifying elements, and the cathodes of the diodes D1 to D4 are connected to the collector of a current driving transistor Q1. It is. The emitter of the transistor Q1 is connected to the ground level via the resistance element R6. The output terminal of the operational amplifier 10 is connected to the base of the transistor Q1. The inverting input terminal of the operational amplifier 10 is connected to the emitter of the transistor Q1 via the resistance element R5, and the non-inverting input terminal applies a reference voltage Vref. As a result, a constant current driving circuit that supplies a constant current (for example, about 1 to 2 A) to the entire LEDs 1 to 4 is configured.

  One end of each of the resistance elements R1, R2, R3, and R4 is connected to each cathode of the LEDs 1 to 4, and the other ends of the resistance elements R1, R2, R3, and R4 are connected to the microcomputer 50. The microcomputer 50 detects the voltages of the cathodes of the LEDs 1 to 4 via the resistance elements R1, R2, R3, and R4. The microcomputer 50 includes an analog / digital conversion circuit for converting an input voltage into a digital value. Moreover, the input of the resistance elements R1, R2, R3, and R4 to the microcomputer 50 may be input by dividing a voltage with a resistor.

  The regulator 20 is connected between the voltage Vdd and the ground level, and the output line S of the microcomputer 50 is connected to one end of the regulator 20. The configuration for detecting the cathode voltage of each LED 1 to 4 is not limited to the resistance elements R 1 to R 4, and a voltage conversion circuit is configured by combining other resistance elements with each of the resistance elements R 1 to R 4. Thus, it can be configured to detect the voltage.

  FIG. 2 is a circuit diagram showing a main configuration of the regulator 20. The regulator 20 has one end of the resistance element R20 connected to the voltage Vdd. One end of resistance elements R21, R22, R23, R24, R25 (for example, R21 <R22 <R23 <R24 <R25) is connected to the other end of the resistance element R20, and the resistance elements 21, R22, R23, R24 are connected. The collectors of transistors Q21, Q22, Q23, Q24, and Q25 as switching elements are connected to the other end of R25, and the emitters of the transistors Q21 to Q25 are connected to the ground level. The bases of the transistors Q21 to Q25 are connected to the output line S of the microcomputer 50. Each of the transistors Q21 to Q25 is configured so that one of them is turned on and the rest are turned off in accordance with the output from the microcomputer 50.

  Next, the operation of the driving apparatus 100 according to the present invention will be described. FIG. 3 is an explanatory diagram showing a method for reducing the power loss generated in the transistor Q1. In FIG. 3, although the circuit in series with LED1 is demonstrated, it is the same also about other LED2-4. As shown in FIG. 3A, LED1, diode D1, collector / emitter of transistor Q1, and resistance element R6 are connected in series between voltage Vdd and the ground level. If the forward voltage of LED1 is Vf, the forward voltage of diode D1 is Vd, the voltage between the emitter and collector of transistor Q1 is Vce, and the voltage across resistor element R6 is Vr, then Vdd = Vf + Vd + Vce + Vr.

  Assuming that the current flowing through the collector of the transistor Q1 with the LEDs 1 to 4 turned on is Ic, the transistor Q1 causes a power loss of W = Ic × Vce. In order to light up each LED1-4 with the required brightness, the current Ic flowing through the collector must be set to a required value, and in order to reduce the power loss in the transistor Q1, It is necessary to lower the emitter-collector voltage Vce.

  As shown in FIG. 3B, in order to reduce the emitter-collector voltage Vce of the transistor Q1 (eg, 0 V), the voltage Vdd is the forward voltage Vf of the LED 1, the forward voltage Vd of the diode D1, and the resistance. The voltage Vdd may be lowered so as to be equal to the sum of the voltages Vr across the element R6. That is, if the original voltage Vdd is reduced by Vce, the emitter-collector voltage Vce of the transistor Q1 becomes equal to zero.

  The microcomputer 50 compares the detected voltage with a threshold value Vth1 (for example, Vth1 = Vd + Vr), and turns on one of the transistors Q21 to Q25 of the regulator 20 according to the difference between the detected voltage and the threshold value Vth1. The other transistors are controlled to be turned off.

  For example, when the difference between the detection voltage and the threshold value Vth1 is relatively small, the transistor Q25 is turned on and the other transistors Q21 to Q24 are turned off. As a result, the voltage Vdd is shunted between the resistor element R20 and the resistor element R25 having a relatively large resistance value, so that the amount of decrease in the voltage Vdd can be made relatively small.

  On the other hand, when the difference between the detected voltage and the threshold value Vth1 is relatively large, the transistor Q21 is turned on and the other transistors Q22 to Q25 are turned off. As a result, the voltage Vdd is shunted between the resistor element R20 and the resistor element R21 having a relatively small resistance value, so that the amount of decrease in the voltage Vdd can be made relatively large. By connecting each of the series circuits of the resistance elements R21 to R25 and the transistors Q21 to Q25 in parallel, the voltage Vdd can be lowered stepwise according to the difference between the detection voltage and the threshold value Vth1, and the transistor Q1 The emitter-collector voltage Vce can be optimized (smallest) according to the detection voltage.

  Thereby, the power loss generated in the transistor Q1 can be reduced, and the heat generation of the transistor Q1 can be suppressed. Further, heat generation can be prevented and reliability can be improved. In addition, it is not necessary to take a heat dissipation measure such as providing a heat dissipation member for the transistor Q1, the structure of the device can be simplified, and the size can be reduced.

  The microcomputer 50 can be configured to detect the voltage of the cathode of each of the LEDs 1 to 4 and compare the lowest voltage among the detected voltages with the threshold value Vth1. Thereby, for example, even when the forward voltage variations of the LEDs 1 to 4 occur, it is possible to prevent the excessive voltage Vdd from being reduced so that the emitter-collector voltage Vce of the transistor Q1 becomes negative. The emitter-collector voltage of the transistor Q1 can be optimally set so that a predetermined current flows through .about.4.

  In addition, it is not limited to the above-mentioned structure, You may abbreviate | omit the diodes D1-D4. Further, the position where the voltage is detected may be only the cathode of any of LEDs 1 to 4. As a result, the number of parts can be reduced and the structure can be simplified, and the apparatus can be realized at low cost.

  In addition, in the example of FIG. 1, the position where the voltage is detected is not limited to the cathode of each LED 1 to 4, and may be the anode of each LED 1 to 4. Further, it may be the collector of the transistor Q1 (in the case of the NPN type), or may be the emitter in the case of the PNP type transistor. In this case, the threshold value Vth1 may be set as appropriate according to the location where the voltage is detected.

  In the example of FIG. 2, the microcomputer 50 is configured to turn on one of the transistors Q21 to Q25 according to the detected voltage. However, the present invention is not limited to this. For example, the resistance elements R21 to R25 are all set to the same resistance value (may be different resistance values), and the microcomputer 50 changes the number of transistors Q21 to Q25 to be turned on according to the difference between the detected voltage and the threshold value Vth1. be able to.

  For example, when the difference between the detection voltage and the threshold value Vth1 is relatively small, only one of the transistors Q21 to Q25 is turned on and the other transistors are turned off. Thereby, voltage Vdd is shunted by the series resistance of resistance element R20 and any one of resistance elements R21 to R25, so that the amount of decrease in voltage Vdd can be made relatively small.

  On the other hand, when the difference between the detection voltage and the threshold value Vth1 is relatively large, for example, all of the transistors Q21 to Q25 are turned on. Thereby, the voltage Vdd is shunted by the series resistance of the resistance element R20 and the parallel circuit of the resistance elements R21 to R25, so that the reduction amount of the voltage Vdd can be made relatively large. By changing the number of transistors Q21 to Q25 that are turned on according to the difference between the detection voltage and the threshold value Vth1, the voltage Vdd can be lowered stepwise, and the emitter-collector voltage Vce of the transistor Q1 can be reduced to the detection voltage. It can be optimized (smallest) depending on.

  FIG. 4 is a circuit diagram showing another example of the configuration of the main part of the driving device 100. As shown in FIG. 4, in the driving apparatus 100, the collector of the transistor Q1 is connected to the voltage Vdd, and the anodes of the LEDs 1 to 3 are connected to the emitter of the transistor Q1 via the resistor element R12. The cathode of each LED 1-3 is connected to the ground level. The output terminal of the operational amplifier 10 is connected to the base of the transistor Q1. The inverting input terminal of the operational amplifier 10 is connected to the emitter of the transistor Q1 via the resistance element R13, and the non-inverting input terminal applies a reference voltage Vref. As a result, a constant current driving circuit for supplying a constant current (for example, about 1 to 2 A) to the entire LEDs 1 to 3 is configured.

  One end of the resistor element R11 is connected to the collector of the transistor Q1, and the other end is connected to the microcomputer 50, and the collector voltage of the transistor Q1 is detected via the resistor element R11. The microcomputer 50 and the regulator 20 are the same as in the example of FIG.

  In this case, assuming that the forward voltage of the LEDs 1 to 3 is Vf, the voltage between the emitter and the collector of the transistor Q1 is Vce, and the voltage across the resistance element R12 is Vr, Vdd = Vf + Vce + Vr. In order to reduce the emitter-collector voltage Vce of the transistor Q1 (for example, 0 V), the voltage Vdd is equal to the sum of the forward voltage Vf of the LEDs 1 to 3 and the voltage Vr across the resistor element R12. Can be lowered. That is, if the original voltage Vdd is reduced by Vce, the emitter-collector voltage Vce of the transistor Q1 becomes equal to zero.

  The microcomputer 50 compares the detected voltage with a threshold value Vth2 (for example, Vth2 = Vf + Vr), and turns on one of the transistors Q21 to Q25 of the regulator 20 according to the difference between the detected voltage and the threshold value Vth2. The other transistors are controlled to be turned off.

  For example, when the difference between the detection voltage and the threshold value Vth2 is relatively small, the transistor Q25 is turned on and the other transistors Q21 to Q24 are turned off. As a result, the voltage Vdd is shunted between the resistor element R20 and the resistor element R25 having a relatively large resistance value, so that the amount of decrease in the voltage Vdd can be made relatively small.

  On the other hand, when the difference between the detected voltage and the threshold value Vth2 is relatively large, the transistor Q21 is turned on and the other transistors Q22 to Q25 are turned off. As a result, the voltage Vdd is shunted between the resistor element R20 and the resistor element R21 having a relatively small resistance value, so that the amount of decrease in the voltage Vdd can be made relatively large. By connecting each of the series circuits of the resistance elements R21 to R25 and the transistors Q21 to Q25 in parallel, the voltage Vdd can be lowered stepwise in accordance with the difference between the detected voltage and the threshold value Vth2. The emitter-collector voltage Vce can be optimized (smallest) according to the detection voltage.

  Thereby, the power loss generated in the transistor Q1 can be reduced, and the heat generation of the transistor Q1 can be suppressed. Further, heat generation can be prevented and reliability can be improved. In addition, it is not necessary to take a heat dissipation measure such as providing a heat dissipation member for the transistor Q1, the structure of the device can be simplified, and the size can be reduced.

  In the embodiment described above, a plurality of LEDs are connected in parallel. However, the number of LEDs is not particularly limited, and may be one. In addition, a constant current element such as an organic EL element can be used as a load instead of the LED. The driving device according to the present invention can be applied not only to a lighting device but also to a display device using LEDs.

It is a circuit diagram which shows the principal part structure of the drive device which concerns on this invention. It is a circuit diagram which shows the principal part structure of a regulator. It is explanatory drawing which shows the method of reducing the power loss which arises in a transistor. It is a circuit diagram which shows the other example of a principal part structure of a drive device.

Explanation of symbols

1, 2, 3, 4 LED
D1, D2, D3, D4 Diode R1-R6 Resistance element R11-R13 Resistance element Q1 Transistor (constant current element)
10 operational amplifier 20 regulator 50 microcomputer

Claims (6)

  A driving device characterized in that power loss caused by a constant current element that supplies a predetermined current to a load such as an LED can be reduced. In a driving device including a constant current element for supplying a predetermined current to a load such as an LED,
A voltage supply unit having a variable voltage supplied to the load;
A voltage detector for detecting a voltage applied to the constant current element;
A comparison unit that compares the voltage detected by the voltage detection unit with a predetermined threshold;
And a control unit configured to control the voltage applied to the constant current element to be lowered by changing a voltage supplied to the load based on a result of comparison by the comparison unit. The constant current element is a transistor connected in series to the load;
The voltage detector is
3. The driving device according to claim 2, wherein the driving device is configured to detect a voltage of an anode or a cathode of the load or a collector or an emitter of the transistor. The voltage supply unit
The voltage supplied to the load is divided by a circuit in which a plurality of series circuits of resistance elements and switching elements having different resistance values are connected in parallel,
The controller is
4. The drive device according to claim 2, wherein the switching device is configured to control any one of the switching elements to be turned on based on a result of comparison by the comparison unit. 5. The voltage supply unit
The voltage supplied to the load is divided by a circuit in which a plurality of series circuits of a resistance element and a switching element are connected in parallel.
The controller is
4. The drive device according to claim 2, wherein the number of switching elements to be turned on is controlled based on a result of comparison by the comparison unit. 5.   An illuminating device comprising the driving device according to any one of claims 1 to 5.

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