JP3571817B2 - Power supply for driving LCD - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a power supply device for driving a liquid crystal panel, and more particularly, to a power supply device for supplying power to a liquid crystal panel, the power supply device having a plurality of power supply outputs, and changing the plurality of outputs at a predetermined timing, or to meet external conditions such as an ambient temperature of the liquid crystal panel. The present invention relates to a power supply for driving a liquid crystal panel, which is suitable for varying the respective voltages.
[0002]
[Prior art]
Conventionally, a power supply device of this type having a configuration shown in FIG. 4 is known. FIG. 4 illustrates an example of the configuration of the liquid crystal panel driving device with a focus on the liquid crystal panel driving power supply device. In FIG. 4, a DC output obtained by rectifying an AC input by a rectifier circuit A, an inrush control unit B and a capacitor C1 is turned on and off by a field effect transistor (FET) Q1 to turn a primary winding N1 of a converter transformer T1. , And controls their outputs to predetermined voltages through rectifier circuits composed of diodes D2 to D5 and capacitors C2 to C5 connected to the output windings N2 to N5 of the transformer T1. To the output voltage control circuits 1 to 4.
[0003]
The output voltage control circuits 1 to 4 rectify the outputs of the respective windings N2 to N5 of the converter transformer by the above-described rectifier circuit and sequentially accumulate the voltages. DC outputs (power supply for liquid crystal) Vout1 to Vout4 are predetermined required for driving the liquid crystal. Voltage conversion is performed for each winding so as to obtain a voltage.
[0004]
At the same time, in the transformer T1, a DC output Vout5 as a power source for a backlight of the liquid crystal panel 10 is obtained from the output winding N6 of the transformer T1 via a rectifier circuit including a diode D6 and a capacitor C6. In the conventional example, the control circuit CNT controls the output voltage Vout5 for the backlight to a predetermined voltage by feeding back the output voltage Vout5 via the voltage detection circuit 6 and the photocoupler P1. The backlight lighting control circuit 7 converts a DC power supply obtained by rectifying the output of the output winding N6 into a voltage. The backlight 8 is lit with the voltage converted to the voltage required for lighting by the lighting control circuit 7. Further, the lighting control circuit 7 receives a control voltage from the MPU 9 for controlling lighting and extinguishing and adjusting brightness.
[0005]
In the apparatus shown in FIG. 4, a liquid crystal drive control circuit 5 for driving liquid crystal is further connected to the plurality of liquid crystal power supplies Vout1 to Vout4. The liquid crystal drive control circuit 5 includes a liquid crystal voltage control circuit 51 and a liquid crystal drive circuit 52. The liquid crystal drive control circuit 5 changes the output voltage at a predetermined timing based on the plurality of liquid crystal power supplies Vout1 to Vout4 to drive the liquid crystal panel. , A plurality of output voltages, the drive timings, and the like are varied according to an external environment such as an ambient temperature.
[0006]
As described above, a power supply device, particularly a power supply device for a liquid crystal panel or the like, usually has a plurality of outputs, and each output voltage is obtained by temporarily converting a rectified voltage of each winding to a predetermined voltage value for each winding. The liquid crystal panel is driven through a liquid crystal voltage control circuit 51 and a liquid crystal drive circuit 52 that perform voltage control and then change the output voltage according to a predetermined timing or input condition according to a signal from the MPU 9. It is the current situation.
[0007]
In addition, control under external input conditions and the like is usually performed by, for example, control of the MPU 9. For example, a plurality of output voltages and drive timings are controlled in accordance with an external environment such as a temperature of a liquid crystal panel and an ambient temperature. Is variable.
[0008]
[Problems to be solved by the invention]
By the way, the power supply device for the liquid crystal panel and the like has the following problems. That is,
1. At present, once a predetermined voltage is output in order to vary a plurality of output voltages according to an external environment such as an ambient temperature, a voltage control circuit is provided to change the output voltage to an arbitrary voltage. In addition, since the control of each output is externally performed by, for example, the control of the CPU, the control voltage must control a predetermined voltage variable width by the output voltage of the CPU.
2. When viewed from the power supply device side, a plurality of power supply outputs such as a liquid crystal drive and a backlight are usually required, and the surroundings of the power supply become complicated, which may hinder miniaturization and further increase the cost.
[0009]
3. In addition, from the viewpoint of the entire device, even a power supply for driving the liquid crystal alone has a plurality of control circuits, which is an obstacle to miniaturization as in the case of the above 2.
[0010]
The present invention has been made in order to solve the problems in the above-described conventional example, and can simplify and miniaturize a control circuit of a power supply for driving a liquid crystal, and can perform external control of a liquid crystal driving voltage. To provide a power supply for driving a liquid crystal that can be performed directly by a power supply, and to perform the above-described voltage control not only between the output terminals but also with reference to another specific voltage. An object of the present invention is to realize a circuit configuration that can be performed without largely changing the configuration of the example.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a liquid crystal panel driving power supply device according to the present invention comprises a converter transformer and a primary voltage conversion means for generating a first DC output obtained by converting a DC voltage of a predetermined DC power supply (main power supply). And a plurality of secondary voltage converters each supplied with the first DC output, wherein the primary voltage converter has a voltage controller for controlling the voltage of the first DC output. The voltage controlled DC output is The powered as power for back light of a liquid crystal panel, the output of the second voltage converting means is characterized in that a plurality of power supply for LCD panel driving. As the predetermined DC power supply, a DC power supply such as a primary or secondary battery, a solar cell, a DC generator, or a DC power supply obtained by rectifying and smoothing a commercial AC power supply with a rectifier and a capacitor can be used.
[0012]
In a preferred embodiment of the present invention, before Symbol respective secondary voltage converting means controls the output voltage in response to a control signal supplied from the CPU for controlling the operation of the liquid crystal panel. The control signal of the CPU is supplied to vary each output of the plurality of power supplies at a predetermined timing or to vary each output of the plurality of power supplies according to external conditions such as the ambient temperature of the liquid crystal panel. As the control signal, in order to maintain compatibility with the conventional example, for at least one of the secondary voltage converting means, the output voltage of the secondary voltage converting means and the output voltage of the other secondary voltage converting means are used. A voltage signal corresponding to the difference voltage is supplied. In this case, the secondary voltage control means includes a differential amplifier means for detecting a difference voltage between an output voltage of the secondary voltage control means and an output voltage of the other secondary voltage conversion means. It comprises voltage comparing means for comparing with a control signal, and voltage controlling means for outputting a voltage controlled according to the output of the voltage comparing means. As these secondary voltage control means, a series control type regulator or a switching type regulator can be used. In these regulators, the voltage comparison means operates as an error amplifier that detects an error between an actual output voltage and a voltage specified by a control signal from the CPU.
[0013]
[Action]
According to the above configuration, the primary voltage conversion means converts the DC voltage of the DC power supply, which is the main power supply, such as a DC power supply obtained by rectifying the AC power supply, into a voltage-controlled first DC output. The first DC output is used as a backlight power source and is input to a plurality of secondary voltage conversion units. The plurality of secondary voltage converters each convert the first DC output into a predetermined DC output, and the DC outputs of these secondary voltage converters are a plurality of DC outputs required for driving the liquid crystal panel. Ru is supplied to the liquid crystal panel driving apparatus as.
[0014]
Conventionally, the primary voltage conversion means has at least the number of output windings corresponding to each secondary voltage conversion means and a rectifying and smoothing circuit. On the other hand, according to the present invention, only one output is required to be connected to the plurality of secondary voltage converters of the primary voltage converter. That is, one output winding and one rectifying / smoothing circuit, which are required in the conventional example, are sufficient, and the circuit configuration is simplified. Furthermore, according to the present invention, the secondary voltage converting means for power and input power for the secondary voltage converting means separate power such as a backlight source, i.e., it is also used as a primary voltage converting means 2 A dedicated power supply for the next voltage conversion means is not required, the output winding and the rectifying and smoothing circuit are further reduced by one, and the circuit configuration is further simplified. In particular, the smoothing capacitor is large compared to other electronic components, and the reduction in the number of used smoothing capacitors greatly contributes to downsizing of the device.
[0015]
Further, since the plurality of secondary voltage conversion means can individually control their outputs, by supplying an external control signal from a CPU or the like to these secondary voltage conversion means, the external control of the liquid crystal drive voltage can be performed. Can be performed directly by the power supply. That is, it is not necessary to provide a separate liquid crystal voltage control circuit for varying the liquid crystal drive voltage in the liquid crystal drive control circuit according to the external environment, and the circuit configuration can be simplified and the device can be downsized. Even when an external control signal indicating a difference voltage between the output voltages is supplied from the CPU or the like as in the conventional example, if the external control signal is converted into a signal indicating each output voltage itself, the conventional example can be used. Can be generated, and compatibility with the conventional example can be maintained.
[0016]
Embodiment 1
FIG. 1 shows a configuration of a power supply device according to one embodiment of the present invention. 1, the same or corresponding members as in FIG. 4 are denoted by the same reference numerals as in FIG.
[0017]
In the circuit of FIG. 1, four power supply voltages Vout1 to Vout4 are output from the AC input and applied to the liquid crystal panel. Further, Vout5 is in this embodiment is used as a power source for driving the backlight. In this circuit, the rectifier circuit A from the AC input, inrush control circuit B, the transformer T1 constitute a rectifier circuit by the capacitor C1, diode D 6, power backlight which is constituted by rectifier circuit of the capacitor C 6 The output voltage Vout5 is controlled to a predetermined value by the voltage detection circuit 6, the control circuit CNT on the primary side of the power supply and the switching FET via a voltage feedback system connected to the photocoupler P1. The output of the four shown by Vout1~Vout4 is being applied to the liquid crystal panel via the liquid crystal driving circuit as described above, the following will describe this operation.
[0018]
First, the output circuit 1 of the voltage Vout1 includes resistors R1 to R4, an operational amplifier Q1, and a voltage control unit 11, and a control voltage from an MPU (not shown in this drawing) is applied to a control signal input terminal Vcont1. A voltage obtained by dividing the control voltage Vcont1 by the resistors R1 and R2 is applied to the input of the operational amplifier Q1. A value obtained by dividing the output voltage Vout1 by the resistors R3 and R4 is input to the other input of the operational amplifier Q1, and a comparison result between the two values is input to the voltage control unit 11. The voltage control unit 11 internally controls the voltage according to the comparison result, and thereby the output circuit 1 has a circuit configuration that outputs a voltage output Vout1 corresponding to the value of the control signal Vcont1.
[0019]
Next, the output circuit 2 for the voltage Vout2 includes resistors R5 to R11, operational amplifiers Q2 to Q3, and a voltage control unit 12. A control voltage from the MPU is applied to the control signal input terminal Vcont2, and the resistance of the control voltage Vcont2 is The voltage divided by R10 and R11 is applied to the input of the operational amplifier Q3. The other input of the operational amplifier Q3 receives a value obtained by dividing the output of the differential amplifier composed of the operational amplifier Q2 and the resistors R5, R6, and R7 by the resistors R8 and R9, and determines the comparison result of the voltage Q3 by voltage control. Input to the unit 12. As a result, the voltage of the output Vout2 is controlled to a value corresponding to the control voltage from the MPU of Vcont2.
[0020]
Here, in the differential amplifier composed of the operational amplifier Q2 and the resistors R5, R6, and R7, the output Vout1 of the output circuit 1 is input to one input of the operational amplifier Q2 via the resistor R6, and the other input is Vout2, which is the output of the output circuit 2, is input via the resistor R5. A resistor R7 is connected between the output of the operational amplifier Q2 and the one input terminal. Thus, the output circuit 2 controls the voltage by taking the difference between the output voltage Vout1 of the output circuit 1 and the output of the output Vout2 of the output circuit 2.
[0021]
Similarly, the output circuit 3 of the voltage Vout3 includes resistors R12 to R18, operational amplifiers Q4 to Q5, and a voltage control unit 13, and a control voltage from the MPU is applied to the control signal input terminal Vcont3. The basic operation of the circuit 3 is the same as that of the output circuit 2 described above.
[0022]
Similarly, the output circuit 4 for the voltage Vout4 includes resistors R19 to R25, operational amplifiers Q6 to Q7, and the voltage control unit 14, and a control voltage from the MPU is applied to the control signal input terminal Vcont4. The basic operation of the circuit 4 is the same as that of the output circuit 2 described above.
[0023]
In this embodiment, in the liquid crystal driving, the output voltage Vout1 of the output circuit 1 is controlled by the control voltage from the MPU so that the voltage between the output terminal Vout1 and the ground is controlled, and the output circuit 2 is controlled by the control voltage Vcont2 from the MPU. It controls the voltage between the outputs Vout2 and Vout1. Further, in the output circuit 3, the control voltage Vcont3 from the MPU controls the voltage between the outputs Vout3 and Vout2, and in the output circuit 4, the control voltage Vcont4 from the MPU controls the voltage between the outputs Vout4 and Vout3. It takes shape. In this way, the respective outputs Vout1 to Vout4 are controlled to form an output Vout2 in a form in which a voltage corresponding to the control voltage Vcont2 is stacked on the output Vout1, and a form in which voltages in accordance with the control voltages Vcont3 and Vcont4 are further stacked. As a result, the outputs become Vout3 and Vout4. In this way, each voltage is voltage-controlled between the adjacent output voltage and this voltage is applied to the liquid crystal panel.
[0024]
FIG. 2 shows a configuration in which the embodiment of FIG. 1 is rewritten according to FIG. 4 showing a conventional example. A comparison between FIG. 2 and FIG. 4 shows that in the apparatus of FIG. 2, the windings N2 to N5, the diodes D2 to D5, the capacitors C2 to C5, and the liquid crystal voltage control circuit 51 of FIG. Thus, according to the present embodiment, the circuit configuration is simplified as compared with the conventional example.
[0025]
Embodiment 2
The configuration of the first embodiment has been described with a configuration similar to the configuration of FIG. 4 which is a conventional example. Next, another example will be described as a second embodiment.
[0026]
In the first embodiment, the difference between the adjacent outputs is controlled. However, the difference may be different from another output, or another output voltage may be controlled based on a predetermined output. is there. This is effective when, for example, a liquid crystal panel or the like changes other outputs under various conditions based on a predetermined output voltage.
[0027]
FIG. 3 is a diagram showing the above connection example as a second embodiment. 3 differs from that of FIG. 1 in the control signal from the MPU, but the basic operation is the same as that of FIG. In the output circuit 4 of FIG. 3, the difference between the output voltage Vout4 of the output circuit 4 and the output voltage Vout2 of the output circuit 2 is compared by a differential amplifier composed of an operational amplifier Q6 and resistors R19 to R25. Further, the output of the operational amplifier Q6 is compared with a control voltage Vcont4 from an MPU (not shown here) by the operational amplifier Q7 and the resistors R22, R25, R24 and R23, and the output Vout4 is voltage-controlled by the voltage control unit 14. . Further, the voltage control units 11 to 14 can be of either a series regulator type or a switching type, and the same applies to the first embodiment.
[0028]
【The invention's effect】
According to the present invention, the following effects can be obtained.
[0029]
With the power supply device of the present invention, it is possible to easily change the voltage of a plurality of outputs under external conditions, and at the same time, it is possible to control the voltage of each output from the difference between an arbitrary output and the liquid crystal drive. In this case, it becomes easy to change the voltage with a specific output.
[0030]
Further, as compared with the conventional example, the control circuit of the power supply for driving the liquid crystal can be simplified, and the power supply can be configured at a reduced size and at low cost.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a power supply device according to one embodiment of the present invention.
FIG. 2 is a block diagram showing the circuit arrangement of FIG. 1 rewritten according to the conventional example of FIG.
FIG. 3 is a circuit diagram showing a configuration of a power supply device according to another embodiment of the present invention.
FIG. 4 is a block diagram showing a conventional liquid crystal panel driving device, mainly showing a power supply unit thereof;
[Explanation of symbols]
1, 2, 3, 4: output circuit, 5: liquid crystal drive control circuit, 6: voltage detection circuit, 7: backlight lighting control circuit, 8: backlight, 9: MPU, 10: liquid crystal panel, 11, 12, 13, 14: voltage control unit, 51: liquid crystal voltage control circuit, 52: liquid crystal drive circuit, A: rectification circuit, B: rush control unit, CNT: control circuit, P1: photocoupler, T1: inverter transformer.

Claims (8)

Primary voltage conversion means having a converter transformer and generating a first DC output obtained by converting a DC voltage of a predetermined DC power supply; and a plurality of secondary voltage conversion means supplied from the first DC output. And
The primary voltage conversion means has a voltage control means for controlling a voltage of the first DC output, and the voltage-controlled DC output is supplied as a power supply for a backlight of the liquid crystal panel; A power supply for driving a liquid crystal panel, wherein the output of the voltage converting means is a plurality of power supplies for driving the liquid crystal panel. 2. The power supply device according to claim 1, wherein each of the secondary voltage conversion units controls an output voltage thereof in accordance with a control signal supplied from a CPU for controlling an operation of the liquid crystal panel. The power supply device according to claim 2, wherein the control signal is supplied so as to vary each output of the plurality of power supplies at a predetermined timing. 3. The power supply device according to claim 2, wherein the control signal is supplied so as to vary each output of the plurality of power supplies according to an external condition. The power supply device according to claim 4, wherein the external condition is an ambient temperature of the liquid crystal panel. A signal corresponding to the difference between the output voltage of the one secondary voltage converter and the output voltage of the other secondary voltage converter is supplied to the at least one secondary voltage converter as the control signal. The power supply device according to claim 2. The one secondary voltage conversion means detects a difference voltage between its own output voltage and the output voltage of the other secondary voltage conversion means, and an output voltage of the differential amplifier means and the control voltage. 7. The power supply device according to claim 6, further comprising: a voltage comparison unit that compares a voltage specified by the signal with a voltage; and a voltage control unit that outputs a voltage controlled according to an output of the voltage comparison unit. 8. A liquid crystal device comprising a liquid crystal panel, a backlight for illuminating the liquid crystal panel from a back surface, and power supply means for driving the liquid crystal panel and for lighting the backlight, wherein the power supply means is any one of claims 1 to 7. A liquid crystal device characterized by using the power supply device described in (1).

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