JP4245495B2 - Rear light source for display device and display device - Google Patents

Description

  The present invention relates to a back light source of a display device having a transmission structure such as a transmissive liquid crystal display device, and a display device including such a back light source.

2. Description of the Related Art Semiconductor light emitting devices such as LEDs (light emitting diodes) are widely used as backlights (back light sources) for transmissive display monitors such as LCDs (liquid crystal display devices). The brightness can be adjusted by adjusting the forward current flowing through the semiconductor light emitting element or by driving the semiconductor light emitting element in pulses and adjusting the pulse width and pulse interval. For example, white light can be obtained as illumination light by using semiconductor light emitting elements that emit red, green, and blue light, respectively, and mixing the light emitted by the semiconductor light emitting elements.
The color tone of light emitted from a semiconductor light-emitting element varies from element to element, and in order to compensate for this variation, it is also known to set a current value flowing through each semiconductor element to obtain a desired color tone. (See, for example, Patent Document 1).

JP 2001-272938

  However, the light emission characteristics of the semiconductor light emitting element are temperature dependent due to the light emission principle. For this reason, there has been a problem that the color tone of the back light source changes due to variations in the temperature characteristics of each semiconductor light emitting element, along with changes in environmental temperature and changes in internal temperature due to energization. In other words, even if the current value of each semiconductor element is set so that white light can be obtained, if the ambient temperature or internal temperature changes from the time of setting, the illumination light from the back light source changes color due to the difference in temperature characteristics of each element. There was a problem that it would be hard.

  The present invention has been made in view of such problems, and an object of the present invention is a back light source using a semiconductor light emitting device, which can emit illumination light having a constant hue regardless of environmental temperature change or internal temperature change due to energization. It is to provide a back light source that can emit light stably.

In order to solve the above problems, according to the present invention, a plurality of semiconductor light emitting devices that emit light of different colors, and a current adjustment that individually adjusts the value of the forward current flowing between the anode and the cathode of the plurality of semiconductor light emitting devices. Means for determining the temperature of the plurality of semiconductor light emitting elements based on the current flowing between the anode and cathode of the plurality of semiconductor light emitting elements and the voltage between the anode and cathode, and the plurality of semiconductor light emitting elements For each of the plurality of semiconductor light emitting elements, the forward current flows between the anode and the cathode of the semiconductor light emitting element for each of the plurality of semiconductor light emitting elements, and reverse voltage applying means for individually applying a reverse voltage between the anode and cathode of the element. during not, to maintain the temperature of the semiconductor light-emitting element substantially constant on the basis of the temperature determined by said temperature detecting means, the reverse voltage Backlight source for a display device characterized by having a temperature control means for controlling the reverse voltage applied to the semiconductor light-emitting device is provided by the pressure means.

  According to the present invention, it is possible to always display an image with a desired correct color tone regardless of a change in environmental temperature or a change in internal temperature due to energization.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a circuit configuration of a back light source according to Embodiment 1 of the present invention. The rear light source includes semiconductor light emitting elements (for example, light emitting diodes) 2a, 2b, and 2c that emit red, green, and blue light, variable constant current drive circuits 3a, 3b, and 3c, and current value control circuits 5a, 5b, and 5c. Have. A heating resistor (resistive element) 27 is disposed in the vicinity of the semiconductor light emitting element 2a. The heating resistor 27 is driven by a heating resistor driving circuit 26 controlled by the temperature control circuit 25.

  The anode of the semiconductor light emitting element 2a is connected to the power supply terminal 1a, and the cathode is connected to the variable constant current drive circuit 3a. The current supplied from the power supply terminal 1 a to the semiconductor light emitting element 2 a flows through the variable constant current drive circuit 3 a to the common ground terminal 11. The current value control circuit 5a determines a current value to be passed through the semiconductor light emitting element 2a based on a signal input from the common current increase / decrease ratio input terminal 7 and a signal input from the individual current adjustment input terminal 6a, and the semiconductor light emitting element 2a. The variable constant current drive circuit 3a is controlled so that the value of the current flowing in the current becomes equal to the determined current value.

  Similarly, the anode of the semiconductor light emitting element 2b is connected to the power supply terminal 1b, the cathode is connected to the variable type constant current drive circuit 3b, and the current supplied from the power supply terminal 1b to the semiconductor light emitting element 2b is variable type constant current drive circuit. It flows through the common grounding terminal 11 through 3b. The current value control circuit 5b determines a current value to be passed through the semiconductor light emitting element 2b based on the signal input from the common current increase / decrease ratio input terminal 7 and the signal input from the individual current adjustment input terminal 6b, and the semiconductor light emitting element 2b. The variable constant current drive circuit 3b is controlled so that the value of the current flowing through becomes equal to the determined current value.

  Similarly, the anode of the semiconductor light emitting element 2c is connected to the power supply terminal 1c, the cathode is connected to the variable constant current drive circuit 3c, and the current supplied from the power supply terminal 1c to the semiconductor light emitting element 2c is variable variable constant current drive circuit. It flows through the common ground terminal 11 through 3c. The current ground control circuit 5c determines a current value to be supplied to the semiconductor light emitting element 2c based on a signal input from the common current increase / decrease ratio input terminal 7 and a signal input from the individual current adjustment input terminal 6c, and the semiconductor light emitting element 2c. The variable constant current drive circuit 3c is controlled so that the value of the current flowing through is equal to the determined current value.

An output voltage Vcc1 of a power supply (not shown) is applied to the power supply terminal 1a via the current detection resistor 22. The temperature control circuit 25 can detect the value of the current flowing through the semiconductor light emitting element 2 a from the voltage between the terminals of the current detection resistor 22 detected via the signal lines 31 and 32. Further, the temperature control circuit 25 can detect the voltage between the anode and the cathode of the semiconductor light emitting element 2 a via the signal line 32 and the signal line 33.
The current value control circuits 5a to 5c and the variable constant current drive circuits 3a to 3c constitute current value adjusting means. The temperature control circuit 25, the heating resistor driving circuit 26, and the heating resistor 27 constitute temperature control means.

The other semiconductor light emitting elements 2b and 2c are also provided with a temperature control circuit, a heating resistor driving circuit, and the like, similar to the semiconductor light emitting element 2a, but are not shown in FIG. 1 so that the drawing is not excessively complicated.
Below, operation | movement of the back light source of the said structure is demonstrated.

  First, the currents flowing through the semiconductor light emitting devices 2a, 2b, and 2c are individually adjusted by individually adjusting the signals input to the individual current adjustment input terminals 6a, 6b, and 6c while viewing the displayed screen. Adjust the balance. Subsequently, the signal input to the common current increase / decrease rate input terminal 7 is adjusted, and the amount of light, that is, the luminance is adjusted by increasing or decreasing the current flowing through the semiconductor light emitting elements 2a, 2b, and 2c at the same rate.

  From this state, for example, when the temperature of the semiconductor light emitting device changes due to environmental temperature changes or the influence of internal heat generation due to energization, in the conventional back light source, the white balance is lost due to variations in the temperature characteristics of each semiconductor light emitting device was there. On the other hand, in the back light source of the present embodiment, the voltage drop at the semiconductor junction inside the semiconductor light emitting element has a negative temperature characteristic, that is, the resistance value of the semiconductor light emitting element has a negative temperature coefficient. The temperature of the semiconductor light emitting element is determined based on the resistance value obtained from the detected voltage value and current value. When the temperature of the semiconductor light emitting element rises, the temperature control circuit 25 sends an instruction to the heating resistor driving circuit 26 via the signal line 34 to reduce the current flowing through the heating resistor 27 and lower the temperature of the semiconductor light emitting element. . On the contrary, when the temperature of the semiconductor light emitting element is lowered, the temperature control circuit 25 sends an instruction to the heating resistor driving circuit 26 via the signal line 34 to increase the current flowing through the heating resistor 27, so that the temperature of the semiconductor light emitting element is increased. Raise.

According to the present embodiment, as described above, the temperature of the semiconductor light-emitting element is kept substantially constant without being affected by changes in the environmental temperature and internal heat generation due to energization, so that illumination light with a stable color tone can be obtained. It is done.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing a circuit configuration of a rear light source according to the second embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  In the first embodiment, the temperature of the semiconductor light emitting element is controlled by controlling the current flowing through the heating resistor 27, whereas in the present embodiment, a reverse voltage applying element (transistor) 40 serving as a reverse voltage applying means is used. The first embodiment is different from the first embodiment in that the temperature of the semiconductor light emitting element is controlled by controlling the timing of applying the reverse voltage to the semiconductor light emitting element using the. The operation of this embodiment will be described below.

  The temperature control circuit 25 obtains information about whether or not the semiconductor light emitting element is conductive (ie, whether or not forward current is flowing) from the outside via the terminal 45. While a forward current flows through the semiconductor light emitting element, a voltage Vcc2 (Vcc2> Vcc1) of a power source (not shown) is applied to the control line 35 connected to the base of the transistor 40 to which the bias voltage is applied. The voltage level is raised, thereby turning off transistor 40. On the other hand, while no forward current flows through the semiconductor light emitting device, the voltage level of the control line 35 is lowered to turn on the transistor 40. As a result, the voltage Vcc2 applied to the emitter of the transistor 40 is applied from the collector to the cathode of the semiconductor light emitting device. Since the voltage Vcc2 is larger than the voltage Vcc1, a reverse current flows through the semiconductor light emitting element during this period.

  In the second embodiment, for example, when the flow angle (pulse width at the time of pulse width control) is narrow, the forward current flowing through the semiconductor light emitting element is small, and the internal heat generation due to energization decreases, the reverse current increases and the reverse current increases. Increases heat generation due to. Conversely, when the flow angle is wide, the forward current flowing through the semiconductor light emitting element is large, and the internal heat generation due to energization increases, the reverse current decreases and the heat generation due to the reverse current decreases. Therefore, the temperature change of the semiconductor light emitting element due to the wide and narrow distribution angle can be reduced.

In the present embodiment, as in the first embodiment, the temperature control circuit 25 detects the value of the current flowing through the semiconductor light emitting element detected via the signal lines 31, 32, and 33 and between the anode and cathode of the semiconductor light emitting element. The temperature of the semiconductor light emitting element is determined from the voltage of the current, and the value of the reverse current flowing through the semiconductor light emitting element is controlled by adjusting the reverse voltage application time, for example, so that the temperature of the semiconductor light emitting element is kept constant.
In the second embodiment, since the reverse current of the element itself is used for temperature control of the semiconductor light emitting element, the response to the temperature change is fast and the temperature control accuracy is high.

Embodiment 3 FIG.
FIG. 3 is a block diagram showing a circuit configuration of a back light source according to Embodiment 3 of the present invention. In the figure, the same reference numerals are given to the same elements as those shown in FIGS. 1 and 2, and the description thereof is omitted.

  In the third embodiment, a series circuit of a heating resistor 27 and a diode 50 is connected in parallel to the semiconductor light emitting element, and a current is passed through the heating resistor 27 to generate heat while no forward current flows through the semiconductor light emitting element. Thus, the second embodiment is different from the second embodiment.

In the third embodiment, when the flow angle is narrow, the forward current flowing through the semiconductor light emitting element is small, and the internal heat generation due to energization is small, the temperature control circuit 25 increases the current flowing through the heating resistor 27 and Increase calorific value. Conversely, when the flow angle is wide, the forward current flowing through the semiconductor light emitting element is large, and the internal heat generation due to energization is large, the current flowing through the heating resistor 27 is decreased and the amount of heat generated by the heating resistor 27 is decreased. Therefore, as in the second embodiment, in this embodiment, the temperature of the semiconductor light emitting element is stabilized to be substantially constant regardless of the distribution angle, and illumination light having a stable color tone can be obtained.
In the third embodiment, since the heat generated by the heat generating resistor 27 is used, the color tone of the illumination light can be stabilized even if a semiconductor light emitting element having a large variation in reverse current characteristics is used.

  FIG. 4 shows a schematic configuration of a display device having the back light source of each embodiment described above. In FIG. 4, red light, green light, and blue light emitted from each semiconductor light emitting element enter, for example, a light guide sandwiched between a reflector and a diffuser, and are multiple-reflected and mixed in the light guide. The white illumination light obtained thereby illuminates an image forming surface such as a liquid crystal panel disposed opposite to the diffusion plate. The light guide, the diffusion plate, and the reflection plate constitute a mixing unit for the back light source.

It is a circuit block diagram of the back surface light source which concerns on Embodiment 1 of this invention. It is a circuit block diagram of the back surface light source which concerns on Embodiment 2 of this invention. It is a circuit block diagram of the back surface light source which concerns on Embodiment 3 of this invention. It is a figure which shows schematic structure of the display apparatus provided with the back light source.

Explanation of symbols

  1a, 1b, 1c Power supply terminal, 2a, 2b, 2c Semiconductor light emitting element, 3a, 3b, 3c Variable constant current drive circuit, 5a, 5b, 5c Current value control circuit, 6a, 6b, 6c Individual adjustment input terminal, 7 Common current increase / decrease ratio input terminal, 11 ground terminal, 22 current detection resistor, 25 temperature control circuit, 26 heating resistor drive circuit, 27 heating resistor, 40 transistor (reverse voltage applying element), 41 bias resistor, 45 conduction non-conduction information input Terminal, 50 diodes.

Claims (9)

A plurality of semiconductor light emitting elements each emitting light of different colors;
Current adjusting means for individually adjusting the value of forward current flowing between the anode and cathode of the plurality of semiconductor light emitting devices;
Temperature detecting means for determining the temperatures of the plurality of semiconductor light emitting elements based on the current flowing between the anode and cathode of the plurality of semiconductor light emitting elements and the voltage between the anode and cathode;
Reverse voltage applying means for individually applying a reverse voltage between the anodes and cathodes of the plurality of semiconductor light emitting elements to flow a reverse current;
For each of the plurality of semiconductor light emitting elements, the temperature of the semiconductor light emitting element is set based on the temperature determined by the temperature detecting means while the forward current does not flow between the anode and the cathode of the semiconductor light emitting element. A back light source for a display device, comprising: temperature control means for controlling the reverse voltage applied to the semiconductor light emitting element by the reverse voltage application means so as to be maintained substantially constant. The temperature control means has heat generation means arranged in the vicinity of the semiconductor light emitting element,
The back light source according to claim 1, wherein the temperature control unit controls a heat generation amount of the heat generation unit based on the temperature determined by the temperature detection unit .   The back light source according to claim 2, wherein the heat generating unit is formed of a resistance element. The temperature control means has heat generation means arranged in the vicinity of the semiconductor light emitting element,
The temperature control means drives the heat generating means to generate heat while no forward current flows through the semiconductor light emitting element, and generates a heat generation amount of the heat generating means based on the temperature determined by the temperature detecting means. back light source according to claim 1, characterized in that control. 5. The back light source according to claim 4 , wherein the heat generating unit includes a series circuit of a resistance element and a diode connected in parallel to the at least one semiconductor light emitting element. Wherein the plurality of semiconductor light emitting devices, red, green, blue backlight source according to claim 1, any one of 5, characterized by comprising the three kinds of semiconductor light emitting elements that emit each light. Back light source according to any one of claims 1 6, wherein the plurality of semiconductor light emitting element is a light emitting diode. Backlight source according to any one of claims 1 to 7, characterized by further comprising a mixing means for outputting a white illumination light by mixing the light emitted from the plurality of semiconductor light emitting elements. 9. A display device comprising: the back light source according to claim 8 ; and an image forming panel illuminated with illumination light output from mixing means of the back light source.

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