JP2008288396A - Constant current circuit, light emitting device, light emitting device array, color display device, backlight, lighting device - Google Patents

Abstract

A terminal t1, a terminal t2, a transistor TR1 whose collector is connected to the terminal t1, a current detection resistor R1 connected between the emitter of the transistor TR1 and the terminal t2, and a base of the transistor TR1 In a constant current circuit including a resistor R2 connected between the terminal t1 and a light emitting diode LED1 connected between the base of the transistor TR1 and the terminal t2, ON / OFF of the current flowing through the light emitting diode LED1 Make switching easier.
A switching element TR2 connected in parallel to a light emitting diode LED1 is provided.
[Selection] Figure 1

Description

  The present invention relates to a constant current circuit, a light emitting device including the constant current circuit, a light emitting device array, a color display device, a backlight, and a lighting device.

  Conventionally, a light-emitting device using a light-emitting diode has been used. A constant current circuit is known as a circuit for driving a light emitting diode.

  FIG. 3 is a circuit diagram of a constant current circuit disclosed in Patent Document 1.

  As shown in this figure, the constant current circuit of Patent Document 1 includes a constant current transistor TR1 whose collector is connected to a terminal t1, and a current detection transistor connected between the emitter of the constant current transistor TR1 and a terminal t2. A resistor R1, a light emitting diode LED1 for obtaining a reference voltage connected between the terminal t2 and the base of the constant current transistor TR1, and a light emitting diode LED1 connected between the base of the constant current transistor TR1 and the terminal t1. And a resistor R2 for supplying a current to the.

When a voltage is applied between the terminal t1 and the terminal t2 in the above constant current circuit, a current flows to the light emitting diode LED1 through the resistor R2, and a voltage drop of about 1.8 to 2 v occurs in the light emitting diode LED1. At this time, since V _BE of the constant current transistor TR1 is about 0.65V, the voltage applied to both ends of the resistor R1 is about 1.2V. A value obtained by dividing the voltage applied to the resistor R1 by the resistance value of the resistor R1 is a constant current value.

  When the voltage applied between the terminal t1 and the terminal t2 is changed in the constant current circuit, the current flowing through the resistor R2 varies in proportion to the voltage between the terminals, but the voltage across the light emitting diode LED1 does not change much. Therefore, the voltage across the resistor R1 does not change much and the change in the constant current value is small.

Also, when the ambient temperature changes, the temperature characteristics of _{V F} of the light emitting diode LED1 is because _{V BE} temperature coefficient of there about -2 mV / ° C. transistor TR1 also an approximately -2 mV / ° C., and VF temperature characteristics of the light emitting diode LED1 The V _BE temperature characteristics of the transistor TR1 are substantially the same, and the mutual temperature characteristics cancel each other, so that the fluctuation of the constant current can be reduced in a wide temperature range.
Japanese Patent Laid-Open No. 3-23704 (Publication date: January 31, 1991)

  However, the constant current circuit of Patent Document 1 describes that it is possible to monitor the driving state of the constant current circuit by looking at the light emission state of the light emitting diode LED1. It does not describe whether the driving state is controlled.

  The present invention has been made in view of the above-described problems, and its object is to provide a first terminal, a second terminal, a collector side on the first terminal side, and a base side and an emitter side on the first side. A transistor connected to the two-terminal side, a first resistor for current detection connected between the emitter of the transistor and the second terminal, and a base connected to the first terminal of the transistor; A second diode, a first diode connected between the base of the transistor and the second terminal, and applying a voltage between the first terminal and the second terminal to apply the voltage to the transistor. An object of the present invention is to provide a light emitting device including an input circuit that switches ON / OFF of a current flowing through a first diode when a current flowing through the first diode is made constant.

  Further, when the constant current circuit of Patent Document 1 is applied to a configuration used to supply a constant current to a light emitting diode, whether or not the light emitting diode is lit is determined only from the side where the light emitting diode is provided on the substrate. There is a problem that it cannot be confirmed.

  Another object of the present invention is a light-emitting device having a light-emitting diode on a substrate, which can confirm whether or not the light-emitting diode is lit from both the front and back surfaces of the substrate without complicating the device configuration. Is to provide.

  Some light emitting diodes have light emission characteristics that change with temperature. For example, a red light emitting diode generally has a light emission characteristic that the emission intensity decreases when the temperature increases, and the emission intensity increases when the temperature decreases. Green light-emitting diodes generally have a longer emission wavelength when the temperature is higher, and the emission color changes toward red, and when the temperature is lower, the emission wavelength is shorter and the emission color is closer to blue. It has a light emission characteristic that it changes in the following direction. This wavelength shift occurs even when the energizing current is large, and the wavelength becomes shorter as the energizing current increases. Also, in the case of red and green light emitting diodes using a blue light emitting diode as an excitation light source and phosphors, luminous intensity fluctuations occur due to changes in the wavelength of the excitation light source (the luminous intensity decreases at higher temperatures).

  For this reason, when supplying a constant current to a light emitting diode using the constant current circuit of the said patent document 1, there exists a problem that the light emission characteristic of a light emitting diode will change with the change of temperature.

  Still another object of the present invention is to provide a light-emitting device that can compensate for fluctuations in light-emitting characteristics of a light-emitting diode due to temperature changes.

  In order to solve the above problems, the constant current circuit of the present invention has a first terminal, a second terminal, a collector side on the first terminal side, and a base side and an emitter side on the second terminal side. A connected transistor; a first resistor for current detection connected between the emitter of the transistor and the second terminal; and a second resistor connected between the base of the transistor and the first terminal. And a first diode connected between the base of the transistor and the second terminal, and by applying a voltage between the first terminal and the second terminal, a current flowing through the transistor is A constant current circuit configured to be a constant current, comprising a switching element connected in parallel or in series to the first diode and for switching ON / OFF of a current flowing through the first diode. It is set to.

  According to said structure, ON / OFF of the electric current which flows into a 1st diode can be switched by controlling the operation | movement of a switching element.

  A light emitting device according to the present invention includes the constant current circuit according to claim 1 and a light emitting diode connected between the first terminal and the collector of the transistor or a light emitting diode array in which a plurality of light emitting diodes are connected in series. A light-emitting device having a light-emitting unit and a substrate having the constant current circuit and the light-emitting unit, wherein the light-emitting unit and the first diode are provided on different surfaces of the substrate, and the first The diode is a light emitting diode.

  According to said structure, ON / OFF of a light emission part is controllable by controlling ON / OFF of a 1st diode. Therefore, when the first diode is a light emitting diode, the first diode can function as an indicator indicating the ON / OFF state of the light emitting unit. Thus, for example, even when the light emitting unit and the constant current circuit are provided on different surfaces of the substrate, the ON / OFF state of the light emitting unit can be easily identified from both the front and back surfaces of the substrate. it can.

  Moreover, according to said structure, ON / OFF of the electric current which flows into a 1st diode can be easily switched by controlling the operation | movement of a switching element. Thereby, ON / OFF of the said light emission part can be switched easily.

  The light emitting unit may include a light emitting diode array in which a plurality of light emitting diodes are connected in series, and the specifications of the light emitting diodes constituting the light emitting diode array may be the same.

  Further, the light emitting diode may be a light emitting diode that does not include a phosphor, or a light emitting diode that includes a phosphor.

  The light emitting device array according to the present invention includes the constant current circuit, and a light emitting unit including a light emitting diode connected between the first terminal and the collector of the transistor or a light emitting diode array in which a plurality of light emitting diodes are connected in series. A plurality of light emitting devices are provided.

  According to said structure, ON / OFF of the electric current which flows into a 1st diode can be easily switched by controlling the operation | movement of a switching element. Thereby, ON / OFF of the said light emission part in each said light-emitting device can be switched easily.

  The plurality of light emitting devices may include light emitting devices having different light emission colors of the light emitting diodes.

  Among the plurality of light emitting devices, a light emitting device in which the light emitting color of the light emitting diode is red, a light emitting device in which the light emitting color of the light emitting diode is blue, and a light emitting color of the light emitting diode is green. The light emitting device may be included.

  The light emitting units of the plurality of light emitting devices may be mounted on a common package.

  Further, a thermistor resistor whose resistance value changes according to temperature may be used as the first resistor.

  In the above configuration, the voltage across the first resistor for current detection hardly changes. Therefore, as the first resistor for current detection, a thermistor resistance whose resistance value varies with temperature is used to compensate for the temperature dependence of the light emission characteristics of the light emitting diode, and constant light output characteristics over a wide temperature range. Can keep.

  Further, as the first resistor in the light emitting device including a light emitting diode whose emission color is red, a negative thermistor resistor whose resistance value decreases at a high temperature and increases at a low temperature may be used. .

  A light emitting diode whose emission color is red has a light emission characteristic that the emission intensity decreases at a high temperature and the emission intensity increases at a low temperature. Therefore, by using a thermistor resistor having a negative characteristic as the first resistor as in the above-described configuration, it is possible to compensate for fluctuations in emission intensity due to temperature changes of the light emitting diode whose emission color is red.

  In addition, as the first resistor in the light emitting device including the light emitting diode whose emission color is green, a thermistor resistor having a negative characteristic in which the resistance value decreases at a high temperature and the resistance value increases at a low temperature may be used. .

  The light emitting diode whose emission color is green has a light emission characteristic that the emission wavelength becomes longer when the temperature is higher and the emission wavelength becomes lower when the temperature is lower. Further, it has a light emission characteristic that the wavelength is shortened when the energizing current is increased. Therefore, by using a thermistor resistor having a negative characteristic as the first resistor as in the above configuration, it is possible to compensate for fluctuations in the emission wavelength due to a temperature change of the light emitting diode whose emission color is green.

  In addition, the color display device of the present invention includes a light emitting device in which the light emitting color of the light emitting diode is red, a light emitting device in which the light emitting color of the light emitting diode is blue, and a light emitting device in which the light emitting color of the light emitting diode is green. And a light emitting device array.

  The backlight for the liquid crystal display device of the present invention includes any one of the light emitting device arrays described above.

  Moreover, the illumination device of the present invention includes any one of the light emitting device arrays described above.

  The light-emitting device of the present invention includes a light-emitting unit including the constant-current circuit, a light-emitting diode connected between the first terminal and the collector of the transistor, or a light-emitting diode array in which a plurality of light-emitting diodes are connected in series. A thermistor resistor whose resistance value varies with temperature may be used as the first resistor.

  In the above configuration, the voltage across the first resistor for current detection hardly changes. Therefore, as the first resistor for current detection, a thermistor resistance whose resistance value varies with temperature is used to compensate for the temperature dependence of the light emission characteristics of the light emitting diode, and constant light output characteristics over a wide temperature range. Can keep.

  The light emitting diode may have a red light emitting color, and the first resistor may be a thermistor resistor having a negative characteristic in which a resistance value decreases when the temperature becomes high and a resistance value increases when the temperature becomes low.

  A light emitting diode whose emission color is red has a light emission characteristic that the emission intensity decreases at a high temperature and the emission intensity increases at a low temperature. Therefore, by using a thermistor resistor having a negative characteristic as the first resistor as in the above-described configuration, it is possible to compensate for fluctuations in emission intensity due to temperature changes of the light emitting diode whose emission color is red.

  The light emitting diode may emit green light, and the first resistor may be a positive thermistor resistor whose resistance value increases at a high temperature and decreases at a low temperature.

  The light emitting diode whose emission color is green has a light emission characteristic that the emission wavelength becomes longer when the temperature is higher and the emission wavelength becomes lower when the temperature is lower. Therefore, by using a thermistor resistor having a positive characteristic as the first resistor as in the above configuration, it is possible to compensate for a variation in the emission wavelength accompanying a temperature change of the light emitting diode whose emission color is green.

  As described above, the constant current circuit of the present invention includes a switching element that is connected in parallel or in series to the first diode and switches ON / OFF of the current flowing through the first diode.

  Therefore, ON / OFf of the first diode can be easily switched.

  The light-emitting device of the present invention includes the constant-current circuit, a light-emitting unit including a light-emitting diode connected between the first terminal and the collector of the transistor, or a light-emitting diode array in which a plurality of light-emitting diodes are connected in series, A light emitting device having a constant current circuit and a substrate including the light emitting unit, wherein the light emitting unit and the first diode are provided on different surfaces of the substrate, and the first diode is a light emitting diode. is there.

  Therefore, the ON / OFF state of the light emitting unit can be easily identified from both the front and back surfaces of the substrate. Moreover, ON / OFF of a light emission part can be switched easily.

  The light emitting device array according to the present invention includes the constant current circuit, and a light emitting unit including a light emitting diode connected between the first terminal and the collector of the transistor or a light emitting diode array in which a plurality of light emitting diodes are connected in series. A plurality of light emitting devices are provided.

  Therefore, ON / OFF of the light emitting unit in each light emitting device can be easily switched.

  Moreover, the light-emitting device array of this invention is good also as a structure using thermistor resistance from which resistance value changes according to temperature as said 1st resistance.

  In the above configuration, the voltage across the first resistor for current detection hardly changes. Therefore, by using a thermistor resistance whose resistance value varies with temperature as the first resistor for current detection, it is possible to compensate for the temperature dependence of the light emission characteristics of the light emitting diode.

  The light-emitting device of the present invention includes a light-emitting unit including the constant-current circuit, a light-emitting diode connected between the first terminal and the collector of the transistor, or a light-emitting diode array in which a plurality of light-emitting diodes are connected in series. The thermistor resistance whose resistance value changes according to temperature is used as the first resistor.

  Therefore, it is possible to compensate for the temperature dependence of the light emission characteristics of the light emitting diode and maintain a constant light output characteristic over a wide temperature range.

Embodiment 1
An embodiment of the present invention will be described. FIG. 1 is a circuit diagram of a constant current circuit 1 according to the present embodiment.

  As shown in this figure, a constant current circuit 1 includes a constant current transistor TR1 composed of an NPN transistor, an LED array A composed of a plurality of light emitting diodes connected in series, a resistor R1, a resistor R2, a light emitting diode LED1, and a switching transistor. TR2 is provided.

  The light emitting diode LED1 is for obtaining a reference voltage, and the LED array A has a cathode connected to the collector of the constant current transistor TR1 and an anode connected to the terminal t1.

  The resistor R1 is a resistor for current detection, and has one end connected to the emitter of the constant current transistor TR1 and the other end connected to the terminal t2. The terminal t2 is connected to the ground (reference potential).

  The resistor R2 is provided to allow a current to flow through the LED 1, and has one end connected to the terminal t1 and the other end connected to the base of the constant current transistor TR1 and the anode of the light emitting diode LED1.

  The light emitting diode LED1 has an anode connected to the base of the constant current transistor TR1 and a cathode connected to the terminal t2.

  The switching transistor TR2 has a collector connected to the base of the constant current transistor TR1 and an emitter connected to the terminal t2 so as to be in parallel with the light emitting diode LED1. The base of the switching transistor TR2 is connected to the control terminal t3, and a control signal is input from a control circuit (not shown). The control circuit switches (switches) ON / OFF of the switching transistor TR2, for example, by applying a pulse voltage to the control terminal t3. In the present embodiment, an NPN transistor is used as the switching transistor TR2. However, any switching element that can switch the circuit ON (conducting) / OFF (blocking) may be used.

  In the constant current circuit 1, when the switching transistor TR2 is OFF, the light emitting diode LED1 is turned ON (lit), and when a voltage is applied between the terminal t1 and the terminal t2, a constant current flows through the LED array A, and the LED array A turns on (lights up). On the other hand, when the switching transistor TR2 is ON, the light emitting diode LED1 is OFF (not lit), and the LED array A is also OFF (not lit).

  Thereby, the light emitting diode LED1 provided for obtaining the reference voltage can function as an indicator for indicating whether the LED array A is turned on or off. Accordingly, by providing the LED array A and the light emitting diode LED1 on the opposite surfaces of the substrate, it is possible to confirm whether the LED array A is turned on / off from both the front and back surfaces of the substrate.

  In the example of FIG. 1, the NPN constant current transistor TR1 is used, but the present invention is not limited to this. For example, as shown in FIG. 2, a PNP type constant current transistor TR1 may be used.

  In the example of FIG. 2, the resistor R1 has one end connected to the terminal t1 and the other end connected to the emitter of the constant current transistor TR1. The LED array A has an anode connected to the collector of the constant current transistor TR1 and a cathode connected to the terminal t2. The LED 1 has an anode connected to the terminal t1 and a cathode connected to the base of the constant current transistor TR1. The resistor R2 has one end connected to the base of the constant current transistor TR1 and the cathode of the LED 1, and the other end connected to the collector of the switching transistor TR2. The switching transistor TR2 has a collector connected to the other end of the resistor R2, an emitter connected to the terminal t2, and a base connected to the control terminal t3. The operation of the constant current circuit 1 shown in FIG. 2 is substantially the same as the operation of the constant current circuit 1 shown in FIG.

[Embodiment 2]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those shown in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof is omitted.

  In the present embodiment, a color display device 10 including the constant current circuit 1 shown in the first embodiment will be described. In the present embodiment, a configuration using the constant current circuit 1 shown in FIG. 1 will be described. However, the present invention is not limited to this. For example, the constant current shown in FIG. 2 is used instead of the constant current circuit 1 shown in FIG. The circuit 1 may be used.

  FIG. 4 is a circuit diagram showing a configuration of one pixel in the color display device 10, and FIG. 8 is a cross-sectional view showing a schematic configuration of one pixel of the color display device 10.

  As shown in FIG. 4, each pixel of the color display device 10 includes a constant current circuit 1r having a red LED array Ar (LED array Ar made of red chip light emitting diodes) and a green LED array Ag (green chip). A constant current circuit 1g having an LED array Ag made of a light emitting diode and a constant current circuit 1b having a blue LED array Ab (an LED array Ab made of a light emitting diode of a blue chip).

  The constant current circuits 1r, 1g, and 1b have substantially the same configuration as the constant current circuit 1 shown in FIG. However, the constant current circuit 1r has a constant current detection thermistor resistor R3 connected in parallel with the resistor R1 between the emitter of the constant current transistor TR1 and the terminal t2. Different from the current circuit 1. As the thermistor resistor R3, a thermistor resistor having a negative characteristic whose resistance value decreases as the temperature rises is used.

  The color display device 10 includes a large number of pixels having such a configuration, and a control signal corresponding to image data to be displayed from a control circuit (not shown) is sent to each constant current of each pixel via the connector 3 shown in FIG. By sending it to the control terminal of the circuit, the light emission state of the LED array provided in each constant current circuit is controlled to perform full color display.

  FIG. 5 is a graph showing the relationship between luminous intensity and temperature when an LED lamp equipped with a light emitting diode composed of red, green and blue chips not using a phosphor is driven by a constant current circuit of the prior art. . The blue and green light emitting diodes are made of a gallium nitride material.

  As shown in this figure, when the conventional LED lamp is driven by a conventional constant current circuit, a green light emitting diode and a blue light emitting diode can maintain a constant light output in a wide temperature range. However, in a red light emitting diode, the light output increases at low temperatures, and the light output decreases at high temperatures. That is, the temperature characteristics of the light emission output of the light emitting diode not using the phosphor differ depending on the chip material.

  On the other hand, in the constant current circuit 10 according to the present embodiment, the constant current circuit 1 including the red LED array Ar is a negative thermistor resistor whose resistance value decreases as the temperature rises as a current detection resistor. R3 is used. Accordingly, the resistance value of the thermistor resistor R3 is high at low temperatures, and the resistance value of the thermistor resistor R3 is low at high temperatures. Thus, by driving the constant current circuit 1 including the red LED array Ar based on the current value detected using the thermistor resistor R3, the current (LED current) flowing through the LED array A can be reduced at low temperatures. The current flowing through the LED array A can be increased at a high temperature, whereby the temperature characteristics of the light emission output of the LED array A can be corrected.

  FIG. 6 is a graph showing an example of the relationship between the resistance value of the thermistor resistance having a negative characteristic and the temperature. The horizontal axis is the temperature t, and the vertical axis is the resistance value Rt at 25 ° C. when the temperature t is changed. The ratio to R0 (resistance ratio) is shown. The value B shown in FIG. 6 is a constant representing the magnitude of resistance change between any two temperatures in the resistance-temperature characteristics.

  As is clear from comparison between FIG. 5 and FIG. 6, generally, the change due to the temperature change of the resistance value of the thermistor resistance is more remarkable than the change due to the temperature change of the light output of the red LED. Therefore, as shown in FIG. 4, the resistor R2 and the thermistor resistor R3 are configured to be connected in parallel, so that even when a general resistor composed of a carbon film resistor or the like is used as the resistor R2, for example. The temperature characteristic of the combined resistance of R2 and the thermistor resistor R3 can be changed to an appropriate temperature characteristic for correcting the temperature characteristic of the light emission output of the LED array A.

  However, the present invention is not limited to this. For example, as shown in FIG. 7, a resistor R2 and a thermistor resistor R3 may be connected in series. As to whether the resistor R2 and the thermistor resistor R3 are connected in series or in parallel, the temperature characteristic of the combined resistance of the resistor R2 and the thermistor resistor R3 is to correct the temperature characteristic of the light emission output of the LED array A. What is necessary is just to select suitably so that it may become an appropriate temperature characteristic. Further, as the thermistor resistor R3, it is preferable to use a thermistor resistor R3 having a temperature characteristic of a resistance value suitable for compensating for the temperature change of the light output in the red LED array Ar.

  In the green light emitting diode, the light output does not change greatly even when the temperature changes. However, as shown in FIG. 9B, the light emission wavelength varies as the temperature changes. For this reason, in a color display device that performs full-color display using red, green, and blue light emitting diodes, a chromaticity shift occurs due to a change in the emission wavelength of the green light emitting diode. In particular, since green has high visibility, the influence of the chromaticity shift on the wavelength shift is large. For example, even if the red, green, and blue light outputs are balanced at normal temperature and displayed in white, the red light emission output fluctuates due to temperature changes, or the green light emission wavelength changes, causing red, blue, The green color balance is lost, and white cannot be displayed properly.

  Therefore, in the constant current circuit 1 including the LED array Ag made of a green light emitting diode in addition to the configuration shown in FIG. 4 or FIG. 7, the negative characteristic that the resistance value decreases as the temperature rises as a current detection resistor. These thermistor resistors may be provided in parallel or directly with the resistor R2.

  When the temperature becomes high, the current flowing through the green light-emitting diode increases due to the action of the thermistor resistor R2. When the current increases, as shown in FIG. 9A, the wavelength of the green light-emitting diode is shortened, so that the wavelength variation due to temperature (lengthening) is canceled out. Can be suppressed.

  Even in the case of a red light emitting diode using a blue light emitting diode made of a gallium nitride-based material having a small temperature characteristic change as an excitation light source, a red light emitting diode using a green phosphor, and a green light emitting diode, the above-described fluorescence Although the temperature characteristic change is small compared to a light emitting diode that does not use a body, it may be affected by the temperature characteristic of the phosphor. Therefore, in the case where the chromaticity deviation of white light emission is more strictly managed, such as replacement of a fluorescent lamp, the chromaticity deviation accompanying a temperature change becomes a problem.

  In the above configuration, a light emitting diode composed of a blue chip (excitation light source) and a red phosphor may be used as the red light emitting diode, and a negative characteristic thermistor resistor R2 may be provided. Moreover, it is good also as a structure provided with the thermistor resistance R2 of a negative characteristic using the light emitting diode comprised with a blue chip | tip (excitation light source) and a green fluorescent substance as a green light emitting diode.

  In the constant current circuit 1 using a blue chip, since the blue chip as an excitation light source has a high temperature characteristic, the wavelength tends to increase and the luminous intensity tends to decrease. In addition, in the case of a red light emitting diode using a blue light emitting diode made of a gallium nitride-based material with a small temperature characteristic change as an excitation light source, a red light emitting diode using a green phosphor, and a green light emitting diode, the above phosphor Although the temperature characteristic change is small compared to a light emitting diode that does not use, the temperature characteristic of the phosphor may be affected. Therefore, in the case where the chromaticity deviation of white light emission is more strictly managed, such as replacement of a fluorescent lamp, the chromaticity deviation accompanying a temperature change becomes a problem.

  Therefore, as described above, the constant current circuit 1 using a blue chip is provided with the thermistor R2 having a negative characteristic, so that a decrease in luminous intensity due to a longer wavelength due to a temperature change can be corrected.

  In the present embodiment, the color display device 10 that combines LED lamps (LED arrays) mounted with light emitting diodes composed of red, green, and blue chips has been described. However, the scope of application of the present invention is not limited to this. Absent.

  For example, it is applied to a lighting device in which a plurality of light emitting diodes (for example, a light emitting diode made of a red chip (red chip LED) and a light emitting diode made of a green chip (green chip LED)) are mounted on the same substrate. May be.

  Moreover, you may apply to the LED array provided as a light source of the backlight of a liquid crystal display device. Further, the backlight may be, for example, a backlight including a plurality of side light emitting elements on which red, green, and blue chips that do not use a phosphor are mounted.

  Moreover, although each said embodiment demonstrated the constant current circuit for driving the LED array in which several light emitting diodes are connected in series, it does not restrict to this. The present invention can be applied to a constant current circuit for supplying a constant current to one light emitting diode, and supplies a constant current to an LED array (light emitting diode array) in which a plurality of light emitting diodes having the same temperature characteristics are connected in series. It can also be applied to a constant current circuit.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

It is a circuit diagram of the constant current circuit concerning one Embodiment of this invention. It is a circuit diagram of the modification of the constant current circuit concerning one Embodiment of this invention. It is a circuit diagram of the conventional constant current circuit. It is a circuit diagram of the constant current circuit concerning other embodiment of this invention. It is a graph which shows the relationship between the light output of a red, blue, and green light emitting diode, and temperature. It is a graph which shows the relationship between the resistance value of the thermistor resistance which has a negative characteristic, and temperature. It is a circuit diagram of the modification of the constant current circuit concerning other embodiment of this invention. It is sectional drawing of the display apparatus provided with the constant current circuit concerning other embodiment of this invention. (A) is a graph which shows the relationship between the wavelength (peak wavelength) of a green light emitting diode, and an energization current (forward current), (b) is the relationship between the wavelength (peak wavelength) of a green light emitting diode, and temperature. It is a graph which shows.

Explanation of symbols

1, 1r, 1g, 1b Constant current circuit 10 Color display device TR1 Constant current transistor TR2 Switching transistor (switching element)
R1 resistor R2 resistor R3 thermistor resistor (temperature detection resistor)
LED1 LED A, Ar, Ag, Ab LED array

Claims (18)

A transistor having a first terminal, a second terminal, a collector side connected to the first terminal side, a base side and an emitter side connected to the second terminal side, an emitter of the transistor, and a second terminal; A first resistor for current detection connected in between, a second resistor connected between the base of the transistor and the first terminal, and a base connected to the base of the transistor and the second terminal; A constant current circuit including a first diode, and applying a voltage between the first terminal and the second terminal to make a current flowing through the transistor constant.
A constant current circuit comprising: a switching element connected in parallel or in series to the first diode, for switching ON / OFF of a current flowing through the first diode. 2. A constant current circuit according to claim 1, a light emitting part comprising a light emitting diode connected between the first terminal and the collector of the transistor or a light emitting diode array in which a plurality of light emitting diodes are connected in series, and the constant current A light emitting device having a circuit and a substrate including the light emitting unit,
The light emitting device, wherein the first diode is a light emitting diode. The light emitting unit includes a light emitting diode array in which a plurality of light emitting diodes are connected in series,
The light emitting device according to claim 2, wherein the specifications of the light emitting diodes constituting the light emitting diode array are the same.   The light emitting device according to claim 2, wherein the light emitting diode is a light emitting diode that does not include a phosphor.   The light emitting device according to claim 2, wherein the light emitting diode is a light emitting diode including a phosphor.   2. A light emitting device comprising: the constant current circuit according to claim 1; and a light emitting diode comprising a light emitting diode connected between the first terminal and the collector of the transistor or a light emitting diode array in which a plurality of light emitting diodes are connected in series. A plurality of light emitting device arrays.   The light emitting device array according to claim 6, wherein the plurality of light emitting devices include light emitting devices having different light emission colors of the light emitting diodes.   Among the plurality of light emitting devices, a light emitting device in which the light emitting color of the light emitting diode is red, a light emitting device in which the light emitting color of the light emitting diode is blue, and a light emitting device in which the light emitting color of the light emitting diode is green The light-emitting device array according to claim 7, wherein:   The light emitting device array according to claim 6, wherein the light emitting units of the plurality of light emitting devices are mounted in a common package.   9. The light emitting device array according to claim 8, wherein a thermistor resistance whose resistance value varies with temperature is used as the first resistance.   The first resistor in a light emitting device including a light emitting diode whose emission color is red is a thermistor resistor having a negative characteristic in which a resistance value decreases at a high temperature and increases at a low temperature. Item 11. The light-emitting device array according to Item 10.   The positive resistance thermistor resistance, which increases in resistance value at high temperature and decreases in resistance value at low temperature, is used as the first resistance in the light emitting device including a light emitting diode whose emission color is green. Item 11. The light-emitting device array according to Item 10.   A color display device comprising the light-emitting device array according to any one of claims 8, 10, 11, and 12.   The backlight for liquid crystal display devices provided with the light-emitting device array of any one of Claims 6-12.   The illuminating device provided with the light-emitting device array of any one of Claims 6-12. A constant current circuit according to claim 1;
A light emitting diode comprising a light emitting diode connected between the first terminal and the collector of the transistor or a light emitting diode array in which a plurality of light emitting diodes are connected in series;
A light emitting device characterized in that a thermistor resistance whose resistance value varies with temperature is used as the first resistance. The light emitting diode has a red emission color,
17. The light emitting device according to claim 16, wherein the first resistor is a thermistor resistor having a negative characteristic in which a resistance value decreases at a high temperature and increases at a low temperature. The light emitting diode has a green emission color,
17. The light emitting device according to claim 16, wherein the first resistor is a thermistor resistor having a negative characteristic in which a resistance value decreases at a high temperature and increases at a low temperature.

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