JP2007324493A - Light-emitting device, light-emitting element drive circuit, and driving method of light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably drive a semiconductor light emitting element regardless of a change in temperature, and enhance efficiency by reducing the loss of a drive circuit. <P>SOLUTION: A light emitting device is provided with: a light emitting element group 12 with semiconductor light emitting elements 11 connected in series; a constant-current drive circuit 16 that is connected with the light emitting element group 12 to drive the light emitting element group 12 at a constant current; a power supply circuit 20 having an input terminal 21 and an output terminal 22, driving the light emitting element group 12 with the output terminal 22 connected with one end of the light emitting element group 12, supplying the voltage to drive the constant-current drive circuit 16, and outputting the voltage on the basis of the signal input in the input terminal 21; and a temperature compensation circuit 30 detecting the ambient temperature of the light emitting element group 12 to generate temperature signals. The power supply circuit 20 inputs temperature signals in the input terminal of the power supply circuit 20, and controls to decrease the output voltage by the temperature signal having detected a rise in the ambient temperature and increase the output voltage by the temperature signal having detected a fall in the ambient temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting device including a light emitting element such as an LED or an LD, a drive circuit for driving the light emitting element, and a driving method for driving the same.

  A light-emitting device using a semiconductor element as a light-emitting element emits light with a small color, high power efficiency, and vivid colors. In addition, a light-emitting element that is a semiconductor element does not have to worry about running out of a ball, has excellent initial driving characteristics, and has a feature of being strong against vibration and repeated on / off lighting. Because of such excellent characteristics, light-emitting devices using semiconductor light-emitting elements such as light-emitting diodes (LEDs) and laser diodes (LDs) are used as various light sources. In particular, as a result of the development of high-luminance blue LEDs using GaN-based compound semiconductors, LEDs of the three primary colors red (Red), green (Green), and blue (Blue) are available. Display and illumination that can emit full color or white light have been realized.

FIG. 5 shows an LED display using a plurality of LEDs 211 as an example of the light emitting device 200. Shown in this figure. This display can display characters and images by arranging the LEDs 211 in a matrix and controlling the ON / OFF of each LED 211 and the light emission amount. Specifically, a plurality of LEDs 211 are connected in series, and a constant current driving circuit 216 that drives the LEDs 211 at a constant current is connected to the cathode side. By arranging a plurality of such LEDs 211 in parallel and connecting each anode side to the power supply circuit 220, the LED 211 is driven by the output voltage _Vout supplied by the power supply circuit 220.
JP 2005-268622 A Japanese Patent Application Laid-Open No. 9-232074

By the way, the forward voltage V _f varies depending on the temperature of the LED. Specifically, as shown in FIG. 6, the forward voltage V _f of the LED is small during high temperature operation, and the forward voltage V _f is large during low temperature operation. For this reason, the output voltage V _out of the power supply circuit can be obtained so that a plurality of LEDs connected in series with the constant current drive circuit can be driven and a sufficient output voltage V _out that can secure the drive voltage V _dr of the constant current drive circuit itself can be obtained. _out is set.

However, if the output voltage _Vout is increased so as to ensure a sufficient output voltage _Vout even during low temperature operation, the voltage applied to the constant current drive circuit also increases, resulting in heat loss and wasted power consumption. In addition, the amount of heat generated by the circuit also increases, so the stability deteriorates and measures for heat dissipation are required. On the other hand, if the output voltage _Vout is kept low in order to suppress heat loss, the forward voltage _Vf of the LED increases during low temperature operation, so that a sufficient drive voltage _Vdr for driving the constant current drive circuit is secured. There was a problem that the LED could not be driven.

  The present invention has been made in view of such problems. One object of the present invention is to provide a light-emitting device, a light-emitting element drive circuit, and a light-emitting element that can stably drive semiconductor light-emitting elements connected in series regardless of temperature changes, and that increase the efficiency by reducing the loss of the drive circuit. It is to provide a driving method.

  To achieve the above object, a first light emitting device includes a light emitting element group in which semiconductor light emitting elements are connected in series, a constant current driving circuit that is connected to the light emitting element group and drives the light emitting element group at a constant current, A voltage based on a signal input to the input terminal, which has an input terminal and an output terminal, and the output terminal is connected to one end of the light emitting element group to supply a voltage for driving the light emitting element group and driving the constant current driving circuit. And a temperature compensation circuit that detects the ambient temperature of the light emitting element group and generates a temperature signal. The power circuit inputs the temperature signal to the input terminal of the power circuit, and It is possible to control the output voltage to be lowered by the temperature signal that has detected the increase, and to increase the output voltage by the temperature signal that has detected the decrease in the ambient temperature.

  In addition, the second light emitting device includes a plurality of light emitting element groups and these are arranged in parallel to form a light emitting unit, and the plurality of light emitting element groups can be connected in parallel to the power supply circuit.

  Further, in the third light emitting device, the light emitting unit can be configured to arrange a plurality of semiconductor light emitting elements in a matrix.

  Furthermore, in the fourth light emitting device, the ambient temperature can be the temperature of the substrate on which the semiconductor light emitting element is mounted.

  Furthermore, in the fifth light emitting device, the temperature compensation circuit includes a thermistor whose resistance value changes in accordance with a change in ambient temperature. The thermistor has one end connected to the output terminal of the power supply circuit and the other end connected to the second end. The voltage of the first resistor can be input to the input terminal of the power supply circuit as a feedback voltage.

  In the sixth light emitting device, the power supply circuit can be a switching regulator.

  Furthermore, the seventh light emitting device is a light emitting device including a plurality of light emitting diodes, and a plurality of light emitting element groups in which light emitting diodes driven in constant current are connected in series, a light emitting unit connected in parallel, and a light emitting element group A constant current driving circuit for driving the light emitting element group at a constant current, and driving the light emitting element group and an output voltage necessary for driving the constant current driving circuit. Connected to the anode side of the light emitting diode at the other end of the light emitting element group, and a power supply circuit that makes the output voltage variable based on a signal from the input terminal, and a temperature signal for detecting the ambient temperature of the light emitting element group A thermistor is provided, and the temperature signal detected by the thermistor is input to the input terminal of the power supply circuit. The power supply circuit can adjust the output voltage according to the ambient temperature. And the output voltage is lowered, so that the output voltage ambient temperature becomes lower the higher the power supply circuit can control the output voltage.

  The eighth light emitting element driving circuit is a driving circuit for a plurality of semiconductor light emitting elements, and is connected to a light emitting element group in which the semiconductor light emitting elements are connected in series, and is a constant current for driving the light emitting element group at a constant current. The drive circuit has an input terminal and an output terminal. The output terminal is connected to one end of the light emitting element group to supply an output voltage necessary for driving the light emitting element group and driving the constant current drive circuit. A temperature compensation circuit comprising: a power supply circuit that varies an output voltage based on a signal input to a terminal; and a temperature compensation circuit that detects a temperature signal for adjusting the output voltage based on an ambient temperature of the light emitting element group. The temperature signal detected in step 1 is input to the input terminal of the power supply circuit, and the power supply circuit can adjust the output voltage according to the ambient temperature. The output voltage decreases as the ambient temperature increases, and the output voltage decreases as the ambient temperature decreases. As higher, can be the power supply circuit controls the output voltage.

  Furthermore, a ninth light emitting element driving method is a driving method for a plurality of semiconductor light emitting elements, and includes a light emitting element group in which semiconductor light emitting elements are connected in series, and a constant current driving circuit connected to the light emitting element group. The temperature signal related to the ambient temperature of the light emitting element group is detected by supplying the output voltage necessary for driving with the power supply circuit and the temperature compensation circuit connected to the output terminal of the power supply circuit that outputs the output voltage. In addition, the detected temperature signal is input to the input terminal of the power supply circuit. In the power supply circuit, based on the temperature signal, the output voltage decreases as the ambient temperature increases, and the output voltage increases as the ambient temperature decreases. And controlling the output voltage.

  According to the first and seventh to ninth inventions, even if the ambient temperature changes, the power supply circuit controls the output voltage according to the temperature signal detected by the temperature compensation circuit, so that the required output voltage value is adjusted. Unnecessary power loss can be reduced. According to the second invention, a plurality of light emitting element groups can be driven and controlled by a single power supply circuit. According to the third aspect of the invention, a dot matrix display or illumination can be configured. According to the fourth invention, temperature compensation can be realized by detecting the substrate temperature. According to the fifth aspect of the present invention, the output voltage obtained at the output terminal of the power supply circuit is divided by the thermistor that changes the resistance value according to the ambient temperature and the first resistor and is feedback-controlled to the power supply circuit. The output voltage can be increased or decreased according to the ambient temperature. According to the sixth aspect of the invention, the output voltage of the power supply circuit can be easily changed, and a highly efficient power supply circuit can be configured at low cost.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a light emitting device, a light emitting element driving circuit, and a light emitting element driving method for embodying the technical idea of the present invention. The driving circuit and the driving method of the light emitting element are not specified as follows. Further, in the present specification, for easy understanding of the scope of claims, numbers corresponding to the members shown in the embodiments are indicated in the scope of claims and “Means for Solving the Problems”. It is added to the member. However, the members shown in the claims are not limited to the members in the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, and are merely explanations. It's just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Further, in the following description, the same name and reference numeral indicate the same or the same members, and detailed description will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.
(Embodiment 1)

FIG. 1 shows a light emitting device 100 according to Embodiment 1 of the present invention. The light emitting device 100 shown in this figure includes a light emitting unit 10, a temperature compensation circuit 30, and a power supply circuit 20.
(Light Emitting Unit 10)

The light emitting unit 10 is connected in parallel with a light emitting element group 12 in which a plurality of light emitting elements 11 are connected in series.
(Light emitting element 11)

  As the light-emitting element 11 in Embodiment 1, various light-emitting elements such as an LED chip and an LD can be used. These semiconductor light emitting devices have the advantages of excellent output linearity with respect to input, excellent efficiency, long life, and stable use. In Embodiment 1, an LED is used. As this LED, various light-emitting elements are disposed on lead electrodes, packages, and the like, electrically connected, and then covered with a light-transmitting member such as a resin.

The light-emitting element of Embodiment 1 is made of ZnS, SiC, GaN, GaP, InN, AlN, ZnSe, GaAsP, GaAlAs, InGaN, GaAlN, AlInGaP, AlInGaN, etc. on a substrate by liquid phase growth, HDVPE, or MOCVD. What formed the semiconductor as a light emitting layer is used suitably. The emission wavelength of the light-emitting element can be selected from ultraviolet light to visible light and infrared light depending on the material of the semiconductor layer and the degree of mixed crystal. In particular, when a display device that can be suitably used outdoors, a light emitting element capable of emitting light with high luminance is required. Therefore, it is preferable to select a nitride semiconductor as a material of a light emitting element that emits green and blue light with high luminance. For example, In _X Al _Y Ga _1-XY N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, X + Y ≦ 1) can be used as the material of the light emitting layer. Further, a light emitting diode in which such a light emitting element and various phosphors that are excited by the light emission and emit light having a wavelength different from the light emission wavelength of the light emitting element can be combined. It is preferable to select a gallium / aluminum / arsenic semiconductor or an aluminum / indium / gallium / phosphorous semiconductor as a material of a light emitting element emitting red light. For a color display device, it is preferable to combine LED chips having a red emission wavelength of 610 nm to 700 nm, a green emission wavelength of 495 nm to 565 nm, and a blue emission wavelength of 430 nm to 490 nm.

  The light emitting element is electrically connected to a lead electrode that supplies power to the light emitting element, and is covered with a sealing member that protects the light emitting element from the outside, thereby forming a light emitting diode. As the light emitting element, a semiconductor light emitting element in which a semiconductor layer is epitaxially grown on a growth substrate can be suitably used. For the growth substrate, for example, a known material such as sapphire, spinel, SiC, GaN, or GaAs can be used. In addition, by using a conductive substrate such as SiC, GaN, or GaAs instead of an insulating substrate such as sapphire, the p electrode and the n electrode can be arranged to face each other.

Further, if necessary, a wavelength conversion member may be disposed around the light emitting element to convert the light wavelength of the light emitting element, and convert the light to a different wavelength for output. The wavelength conversion member is formed, for example, by mixing in a translucent resin a phosphor that emits fluorescence when excited by the light of the light emitting element 11. Thereby, it becomes possible to convert the light of the light emitting element 11 into light having a longer wavelength, and to extract the mixed color light of the light of the light emitting element 11 and the long wavelength light converted by the wavelength conversion member to the outside.
(Phosphor)

The phosphor converts visible light or ultraviolet light emitted from the light emitting element 11 into another emission wavelength. For example, it is excited by light emitted from the semiconductor light emitting layer of the LED and emits light. Preferred phosphors are YAG phosphors that are rare earth aluminates such as (Y, Gd) ₃ (Al, Ga) ₅ O ₁₂ : Ce that emit light in the yellow region, and alkaline earth silicon nitride fluorescence. Nitride-based phosphors such as phosphors and oxynitride-based phosphors such as alkaline earth silicon oxynitride phosphors can be used. Furthermore, a known phosphor that is excited by ultraviolet light and generates light of a predetermined color can be used.

When the light emitted from the LED chip and the light emitted from the phosphor are in a complementary color relationship or the like, white light can be emitted by mixing each light. Specifically, the light emitted from the LED chip and the phosphor light excited and emitted thereby correspond to the three primary colors of light (red, green, and blue), or the blue light emitted from the LED chip. The light and the yellow light of the fluorescent substance excited and emitted by it are mentioned. In particular, when using ultraviolet light, the emission color of the phosphor excited and emitted by the ultraviolet light can be used independently, so it is possible to realize light emitting devices of various intermediate colors such as blue-green, yellow, red and pastel colors for signals. Is possible.
(Constant current drive circuit 16)

Each light emitting element group 12 is connected to a constant current drive circuit 16. Therefore, the current driver 22 shown in FIG. 1 includes a constant current driver circuit 16 corresponding to the light emitting element group. Each constant current drive circuit 16 serves both as a constant current drive circuit 16 that drives the light emitting element 11 at a constant current, and a control circuit that controls the amount of energization by switching or the like. Here, a MOSFET or a bipolar transistor which is a semiconductor switching element can be used as the driving element.
(Power supply circuit 20)

  The power supply circuit 20 supplies an output voltage for driving the light emitting element group 12 and the constant current drive circuit 16 connected in series. The power supply circuit 20 shown in FIG. 1 includes an input terminal 21 and an output terminal 22, and can output an output voltage from the output terminal 22 and adjust an output voltage based on an input signal to the input terminal 21.

  For the power supply circuit 20, a switching power supply, a linear power supply, a DC / DC converter, or the like can be used as an output variable direct current stabilizing power supply. Here, a switching power supply is used as the power supply circuit 20. Unlike series regulators that release voltage drops as Joule heat, power loss can be reduced, so high accuracy and high efficiency can be obtained. Switching power supplies are also suitable for miniaturization. Here, a switching power supply is configured by the switching regulator IC 23, the rectifier diode 24, the choke coil 25, and the smoothing capacitor 26.

The output voltage V _out is set according to the number of LEDs 11 to be connected and the specification (voltage required for operation) of the constant current drive circuit 16. Here, three LEDs 11 and a constant current drive circuit 16 are connected, and when 24V is applied as an input voltage to the switching regulator IC 23, it is stepped down to output a DC voltage of 12V.
(Temperature compensation circuit 30)

Further, a temperature compensation circuit 30 is connected between the power supply circuit 20 and the light emitting unit 10. The temperature compensation circuit 30 is controlled such that the temperature of the LED 11 is detected and received by the power supply circuit 20 and an appropriate output voltage based on the temperature is applied to the light emitting element group 12. The temperature compensation circuit 30 includes a temperature detection element 31 and a first resistor 32, which divides the output voltage and uses the voltage of the first resistor 32 as a feedback voltage on the input terminal 21 side of the power supply circuit 20. Send it out. Thus, feedback control is performed so that an appropriate output voltage corresponding to the operating temperature of the LED 11 is supplied to the light emitting element group 12 and the constant current drive circuit 16. As a result, a high voltage is unnecessarily applied to the constant current drive circuit 16 to cause heat loss, or conversely, the drive voltage V _dr necessary for driving the constant current drive circuit 16 cannot be secured, resulting in malfunction. It is possible to avoid a situation such as that, and to apply a minimum output voltage to achieve a highly efficient and stable operation.

  In the example of FIG. 1, the temperature compensation circuit 30 includes a thermistor as a temperature detection element 31 and a third resistor 34 in which a resistor R4 is connected in parallel. The third resistor 34 is connected in series with the second resistor 36 and the first resistor 32 and grounded. In this example, the second resistor 36 is formed by connecting resistors R2 and R3 in parallel. The first resistor 32 is constituted by a resistor R1. Further, NCP18XQ102F03RB manufactured by Murata Manufacturing Co., Ltd. was used as the thermistor in the first embodiment.

Further, the connection point between the first resistor 32 and the second resistor 36 is connected to the output terminal 22 of the power supply circuit 20. As a result, the feedback voltage V _fb at the connection point can be sent to the power supply circuit 20 side. In the power supply circuit 20, the voltage input to the input terminal 21 is compared with the reference voltage, and the output voltage is feedback-controlled so that they match. According to this configuration, the output voltage can be adjusted to the optimum value according to the temperature very easily.

The thermistor is disposed close to the LED 11 so that the operating temperature of the LED 11 can be detected. Here, a thermistor is also mounted on the substrate on which the LED 11 is mounted, and the operating temperature of the LED 11 is determined by detecting the temperature of the substrate. Table 1 shows the substrate temperature, the resistance value of the thermistor at this time, the output voltage V _out (rated value) necessary for driving the light emitting element group 12 and the constant current drive circuit 16, and the substrate temperature and the output voltage V _out. FIG. 2 shows the relationship. As shown in these tables and figures, the required output voltage value varies depending on the ambient temperature.

On the other hand, the relationship between the substrate temperature, the output voltage _Vout, and the forward voltage _Vf of the LED 11 in the temperature compensation circuit 30 is shown in Table 2 and FIG. In FIG. 3, the output voltage V _out is indicated by a solid line, and the forward voltage V _f is indicated by a broken line. Further, the forward voltage V _f is represented by the sum of the forward voltages of the three LEDs 11 in FIG. In these tables and figures, the difference between the output voltage V _out and the forward voltage V _{f at} each temperature is the drive voltage V _dr applied to the constant current drive circuit 16.

（比較例）

(Comparative example)

Further, in order to confirm the loss reduction effect by the temperature compensation circuit 30, the driving voltage V _{dr depends on the} substrate temperature between the light emitting device 100 according to the first embodiment and the conventional light emitting device 200 without temperature compensation (FIG. 5). The state in which changes are measured. The results are shown in Table 3 and FIG. In FIG. 4, the solid line indicates the first embodiment, and the broken line indicates the comparative example. In this example, the drive voltage V _dr of the constant current drive circuit 16 is set at a rating of 0.6 V with the goal of applying 1 V in consideration of the margin. The output voltage in the comparative example was fixed at 12V. As a result, in the light emitting device 100 according to the first embodiment in which the temperature compensation is performed, the drive voltage V _dr is maintained substantially constant at around 1 V, whereas in the comparative example, the result is a linear increase with the temperature. It was. For this reason, a driving voltage V _{dr of} 0.6 V cannot be secured at a temperature lower than the substrate temperature of around 13 ° C., resulting in a malfunction. On the other hand, a voltage exceeding 1 V at a substrate temperature of 25 ° C. or higher, and a voltage of 1.88 V at 60 ° C. Was applied to the constant current drive circuit 16, and considerable heat loss occurred. In particular, in LED displays and the like, the inside of the device becomes high temperature due to heat generation, and it is considered that the temperature becomes higher depending on the installation environment. It also affects reliability. On the other hand, in the light emitting device according to the first embodiment, the required minimum constant driving voltage _Vdr can be maintained, and thus a highly efficient and highly reliable light emitting device can be obtained while suppressing loss and heat generation.

  The light-emitting device, the light-emitting element driving circuit, and the light-emitting element driving method of the present invention can be suitably used for a display, an illumination device, and the like using LEDs.

It is a circuit diagram which shows the light-emitting device which concerns on Embodiment 1 of this invention. It is a graph which shows the relationship between board | substrate temperature and output voltage _Vout . It is a graph which shows the relationship between the board _| substrate temperature in a temperature compensation circuit, output voltage _Vout, and the forward voltage _Vf of LED. 4 is a graph showing a relationship between a substrate temperature and a drive voltage V _dr for each of Embodiment 1 and a comparative example. It is a circuit diagram which shows the LED display which uses several LED. It is a graph which shows the temperature characteristic of the forward direction voltage _Vf of LED.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Light-emitting device 11 ... Light-emitting element 10 ... Light-emitting part 11 ... Light-emitting element (LED)
DESCRIPTION OF SYMBOLS 12 ... Light emitting element group 16 ... Constant current drive circuit 20 ... Power supply circuit 21 ... Input terminal 22 ... Output terminal 23 ... Switching regulator IC
24 ... Rectifier diode 25 ... Choke coil 26 ... Smoothing capacitor 30 ... Temperature compensation circuit 31 ... Temperature detection element (thermistor)
32 ... 1st resistor 34 ... 3rd resistor 36 ... 2nd resistor 200 ... Conventional light-emitting device 211 ... LED
216: Constant current drive circuit 220: Power supply circuit

Claims (9)

A light emitting element group in which semiconductor light emitting elements are connected in series;
A constant current driving circuit connected to the light emitting element group and driving the light emitting element group at a constant current;
An input terminal and an output terminal are provided, and the output terminal is connected to one end of the light emitting element group to supply a voltage for driving the light emitting element group and driving the constant current driving circuit, and is input to the input terminal A power supply circuit that outputs a voltage based on the signal;
A temperature compensation circuit that detects an ambient temperature of the light emitting element group and generates a temperature signal;
With
The power supply circuit inputs the temperature signal to the input terminal of the power supply circuit, and controls to lower the output voltage by a temperature signal that detects an increase in ambient temperature, and to increase the output voltage by a temperature signal that detects a decrease in ambient temperature. A light emitting device characterized by: The light-emitting device according to claim 1,
A plurality of the light emitting element groups are provided, and these are arranged in parallel to constitute a light emitting unit,
The light emitting device, wherein the plurality of light emitting element groups are connected in parallel to the power supply circuit. The light-emitting device according to claim 2,
The light emitting unit is configured to arrange a plurality of semiconductor light emitting elements in a matrix. The light-emitting device according to any one of claims 1 to 3,
A light-emitting device, wherein the ambient temperature is a temperature of a substrate on which a semiconductor light-emitting element is mounted. The light-emitting device according to any one of claims 1 to 4,
The temperature compensation circuit includes a thermistor whose resistance value changes according to a change in the ambient temperature,
One end of the thermistor is connected to the output terminal of the power supply circuit, the other end is grounded via a first resistor, and the voltage of the first resistor is used as a feedback voltage for the input terminal of the power supply circuit. A light emitting device characterized by being inputted to the light emitting device. The light emitting device according to any one of claims 1 to 5,
The light-emitting device, wherein the power supply circuit is a switching regulator. A light emitting device comprising a plurality of light emitting diodes,
A plurality of light emitting element groups connected in series with light emitting diodes driven in constant current, a light emitting unit connected in parallel;
A constant current drive circuit connected to the cathode side of the light emitting diode at one end of the light emitting element group, and for driving the light emitting element group at a constant current;
The other end of the light emitting element group is connected to the anode side of the light emitting diode in order to supply the output voltage necessary for driving the light emitting element group and the constant current driving circuit, and based on the signal from the input terminal Power supply circuit that makes the output voltage variable,
A thermistor for detecting a temperature signal related to the ambient temperature of the light emitting element group;
With
The temperature signal detected by the thermistor is input to the input terminal of the power circuit, and the power circuit can adjust the output voltage according to the ambient temperature,
The light-emitting device, wherein the power supply circuit controls the output voltage so that the output voltage decreases when the ambient temperature increases and the output voltage increases when the ambient temperature decreases. A drive circuit for a plurality of semiconductor light emitting elements,
A constant current driving circuit connected to a light emitting element group in which semiconductor light emitting elements are connected in series, and driving the light emitting element group at a constant current;
The output terminal has an input terminal and an output terminal, and the output terminal is connected to one end of the light emitting element group for supplying an output voltage necessary for driving the light emitting element group and driving the constant current drive circuit, A power supply circuit capable of varying the output voltage based on a signal input to the input terminal;
A temperature compensation circuit for detecting a temperature signal for adjusting an output voltage based on an ambient temperature of the light emitting element group; and
With
The temperature signal detected by the temperature compensation circuit is input to the input terminal of the power supply circuit, the power supply circuit is capable of adjusting the output voltage according to the ambient temperature,
The light-emitting element driving circuit, wherein the power supply circuit controls the output voltage so that the output voltage decreases when the ambient temperature increases and the output voltage increases when the ambient temperature decreases. A method for driving a plurality of semiconductor light emitting devices,
Supplying a light emitting element group in which semiconductor light emitting elements are connected in series, and a constant current driving circuit connected to the light emitting element group with an output voltage necessary for driving the power supply circuit;
A temperature compensation circuit connected to an output terminal for outputting an output voltage of the power supply circuit detects a temperature signal related to the ambient temperature of the light emitting element group, and inputs the detected temperature signal to an input terminal of the power supply circuit. In the power supply circuit, the step of controlling the output voltage based on the temperature signal so that the output voltage decreases when the ambient temperature increases, and the output voltage increases when the ambient temperature decreases;
A method for driving a light-emitting element comprising:

Images