JPH07140943A - Current control circuit for liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a current control circuit for a liquid crystal display device capable of reducing power consumption while preventing the abnormal display and the deterioration in a liquid crystal. CONSTITUTION:When a power source to a liquid crystal driving circuit 12 is turned on, an on DISP signal is inputted to the current control circuit 14, and a transistor Tr1 is turned on, and the transistors Tr2, Tr3, Tr4 are turned on, and the transistor Tr5 is turned off. Thus, a liquid crystal driving voltage -VEE' is supplied to the liquid crystal driving circuit 12, and a bleeder resistor Rf is separated from a power source line LD, and the matter that a current flows through the bleeder resistor Rf is impeded. When power source is turned off, the DISP signal is turned off, and the transistor Tr1 is turned off, and the transistors Tr2, Tr3, Tr4 are turned off, and the transistor Tr5 is turned on. Thus, the supply of power source to the liquid crystal driving circuit 12 is stopped, and further, the bleeder resistor Rf is connected to the power source line LD and the power source line LE', and a discharge current If by storage charge on capacitors C12, C13 flows through the bleeder resistor Rf.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control circuit for a liquid crystal display device, and more particularly to a current control circuit for a liquid crystal display device with reduced power consumption.

[0002]

2. Description of the Related Art Recently, for example, in an information processing device represented by a word processor, a personal computer, etc., the display device has been improved in size and weight as the performance and function have been improved. Especially, lightweight and thin ones are desired.

Therefore, an ordinary cathode ray tube (CRT: cath) is used.
Liquid crystal display devices have emerged to become the mainstream of future display devices because they are extremely thin and consume less power than display devices using ode ray tubes.

This liquid crystal display device incorporates a large number of electric field capacitors each having a size of several μF to several tens of μF in order to stabilize display and improve image quality.

However, when the power supply to the liquid crystal panel is turned off, a DC voltage due to a discharge current is applied to the liquid crystal panel from the electric field capacitor, which causes an abnormal display and deteriorates the liquid crystal.

Therefore, conventionally, a bleeder resistance is connected between the power supplies supplied to the liquid crystal drive circuit so that the discharge current of the electric field capacitor flows through the bleeder resistance when the power is turned off.

That is, as shown in FIG. 4, the liquid crystal display device 1 drives the liquid crystal display panel 2 and the liquid crystal display panel 2 by supplying a scanning side drive signal and a signal side drive signal to the liquid crystal display panel 2. A liquid crystal drive circuit 3 and a CPU (Central Processing Unit) 4 for supplying a scan side control signal and a signal side control signal to the liquid crystal drive circuit 3 to control display are provided. A logic voltage VDD and a reference voltage VSS are supplied to the CPU 4 from a power supply circuit (not shown) via a power supply line LD and a power supply line LS.
The liquid crystal drive voltage -VEE is supplied via the power supply line LE, and the logic voltage VDD is supplied via the power supply line LD.

Between the power line LE and the power line LS,
Between the power source line LS, the power source line LD and the power source line LS, and between the power source line LE and the power source line LD, the electric field capacitors C1 and C2 for stabilizing the display of the liquid crystal display panel 2 and improving the image quality. , C3 are connected, and the liquid crystal drive circuit 3 also has a liquid crystal drive voltage -VEE and a logic voltage VDD.
An electric field capacitor C4 indicated by a broken line is connected between the and. The electric field capacitor C4 is a pseudo representation of a plurality of electric field capacitors provided in the liquid crystal drive circuit 3. Further, a bleeder resistor Rf is connected between the power supply line LE and the power supply line LD.

In the liquid crystal display device 1, when the power is turned on, the current I1 is supplied to the liquid crystal drive circuit 3 and the current I2 flows through the bleeder resistance Rf. Then, when the power is turned on, charges are accumulated in each of the electric field capacitors C1, C2, C3 and C4.

After that, when the liquid crystal display device 1 is turned off, the electric charges accumulated in the electric field capacitors C1, C2, C3 and C4 flow into the bleeder resistor Rf as discharge currents I3 and I4, and the liquid crystal display panel. It is possible to prevent an abnormal display from occurring due to the application of a DC voltage due to the discharge current from the electric field capacitors C1, C2, C3, and C4 to 2, and to prevent the liquid crystal from deteriorating.

[0011]

However, in such a conventional liquid crystal display device, only the bleeder resistance is connected between the power supply lines supplied to the liquid crystal drive circuit of the liquid crystal display device. However, when the liquid crystal display device is turned on, current always flows through the bleeder resistor, resulting in an increase in power consumption.

That is, when the liquid crystal display device is powered on, as shown in FIG. 5, a current I2 flows through the bleeder resistor Rf.
Flows and power consumption increases. Therefore, when this liquid crystal display device is driven by a battery, there is a problem that the driving time of the battery is shortened.

In FIG. 5, the current I3 + I4 is
It shows the discharge current flowing through the bleeder resistance Rf when the power is turned off.

Therefore, it is an object of the present invention to provide a liquid crystal display device that consumes less power by preventing a current from flowing through a bleeder resistance during operation of a liquid crystal drive circuit.

[0015]

SUMMARY OF THE INVENTION The present invention is a liquid crystal display in which a resistor for flowing a discharge current from a liquid crystal protection capacitor is inserted between power supply lines for supplying power to a liquid crystal drive circuit for driving a liquid crystal. In the current control circuit of the device, switching means for disconnecting the connection between the power supply line and the resistor when the liquid crystal drive circuit is operating, and for connecting the power supply line and the resistor when the operation of the liquid crystal drive circuit is released. By providing
It has achieved the above objectives.

In this case, the switching means may perform the switching operation by a signal from the control means for controlling the operation of the liquid crystal drive circuit, for example, as described in claim 2. The switching operation may be performed by turning on / off the power supply to the liquid crystal drive circuit, as described in (1).

[0017]

According to the present invention, a resistor for flowing a discharge current from the capacitor for protecting the liquid crystal is inserted between the power supply lines for supplying the power to the liquid crystal drive circuit for driving the liquid crystal, and the switching means is provided. When the liquid crystal drive circuit is operating, the connection between the power supply line and the resistor is disconnected, and when the liquid crystal drive circuit is released from operation, the power supply line is connected to the resistor. Therefore, while preventing abnormal display and deterioration of the liquid crystal, It is possible to prevent a current from flowing through the resistor when the drive circuit is driven, and it is possible to reduce power consumption. As a result, even if the liquid crystal display device is driven by a battery,
It can be driven for a long time.

[0018]

EXAMPLES The present invention will be described below based on examples.

1 to 3 are diagrams showing an embodiment of a current control circuit of a liquid crystal display device according to the present invention.

In FIG. 1, a liquid crystal display device 10 includes a liquid crystal display panel 11, a liquid crystal drive circuit 12, a CPU (Cent).
ral Processing Unit) 13, a current control circuit 14,
Is equipped with.

The CPU 13 is supplied with the logic voltage VDD and the reference voltage VSS from the power supply circuit (not shown) via the power supply lines LD and LS, and the current control circuit 14 is supplied with the logic voltage VDD and the reference voltage. VSS and liquid crystal drive voltage -VEE are supplied. As will be described later, the current control circuit 14 supplies the logic voltage VDD as it is to the liquid crystal drive circuit 12 via the power supply line LD, and supplies the liquid crystal drive voltage -VEE 'to the liquid crystal drive circuit 12 via the power supply line LE'. Supply.

Between the power supply line LE supplying the liquid crystal drive voltage -VEE and the power supply line LS supplying the reference voltage VSS,
Between the power supply line LS and the power supply line LD supplying the logic voltage VDD and the power supply line LS, a smoothing electric field capacitor C10,
C11 is connected, and between the power supply line LE 'and the power supply line LD between the current control circuit 14 and the liquid crystal drive circuit 12, the display of the liquid crystal display panel 11 is stabilized and the image quality is improved. The electric field capacitor C12 is connected. Further, in the liquid crystal drive circuit 12, an electric field capacitor C13 shown by a broken line is connected between the liquid crystal drive voltage -VEE 'and the logic voltage VDD. The electric field capacitor C13 is a pseudo representation of a plurality of electric field capacitors provided in the liquid crystal drive circuit 12.

The CPU 13 outputs a scanning side control signal and a signal side control signal to the liquid crystal drive circuit 12, and the liquid crystal drive circuit 1
It also controls the operation of No. 2 and outputs a DISP signal, which is switched on / off in synchronization with the driving on / off of the liquid crystal drive circuit 12, from the DISP terminal to the current control circuit 14. The DISP signal is an ON signal having the same level as the logic voltage VDD when ON, and an OFF signal having the same level as the reference voltage VSS when OFF.

The liquid crystal drive circuit 12 outputs a scanning side drive signal and a signal side drive signal to the liquid crystal display panel 11 based on the scanning side control signal and the signal side control signal from the CPU 13, and displays on the liquid crystal display panel 11. Let

The current control circuit 14 is configured as shown in FIG. 2, and includes transistors Tr1 and Tr2.
Tr3, Tr4, Tr5, resistors R1, R2, R3, R
4, R5, R6, R7, R8, R9 and a bleeder resistor Rf.

The DISP signal is input to the base of the transistor Tr1 via the resistor R1, and the emitter thereof is connected to the reference voltage VSS. A resistor R2 is connected between the base and the emitter of the transistor Tr1.

The collector of the transistor Tr1 is
The transistor Tr2 is connected to the base of the transistor Tr2 via the resistor R3 and is connected to the transistor Tr2 via the resistor R7.
4 is connected to the base.

A resistor R4 is connected between the base and the emitter of the transistor Tr2, the emitter of which is connected to the logic voltage VDD and the collector of which is connected to the base of the transistor Tr3 via the resistor R5. There is.

The emitter of the transistor Tr3 is
It is connected to the liquid crystal drive voltage -VEE, and when turned on, the liquid crystal drive voltage -VEE is output to the liquid crystal drive circuit 12 from its collector as a liquid crystal drive voltage -VEE 'reduced by its internal resistance. A resistor R6 is connected between the emitter and the base of the transistor Tr3, and its collector is connected to the base of the transistor Tr5 via the resistor R9 and to the collector of the transistor Tr4. It is connected to the collector of the transistor Tr5 via the bleeder resistance Rf.

The emitter of the transistor Tr4 is connected to the logic voltage VDD, and the resistor R8 is connected between the base and the emitter of the transistor Tr4. As described above, the collector of the transistor Tr4 is connected to the base of the transistor Tr5 and is also connected to the collector of the transistor Tr3 via the resistor R9.

As described above, the transistor Tr5 has its base connected to the collector of the transistor Tr3 via the resistor R9 and also has the transistor Tr4.
Is connected to the collector of the transistor Tr3 via the bleeder resistance Rf, and is also connected to the liquid crystal drive circuit 12. The emitter of the transistor Tr5 is connected to the logic voltage VDD and is connected to the liquid crystal drive circuit 12 via the power supply line LD.

The electric field capacitor C12 is connected between the power supply line LE 'and the power supply line LD connected to the liquid crystal drive circuit 12.

Next, the operation of this embodiment will be described.

The current control circuit 14 of the liquid crystal display device 10 of this embodiment blocks the current flowing through the bleeder resistor Rf when the operation of the liquid crystal drive circuit is on, thereby reducing the power consumption.

That is, as shown in FIG. 3, the CPU 13 turns on when the liquid crystal display device 10 is powered on.
When an ON DISP signal is input, the current control circuit 14 disconnects the bleeder resistance Rf from the power supply line LD to prevent a current from flowing through the bleeder resistance Rf.

That is, the ON DISP signal is a signal of the same level as the logic voltage VDD, and as shown in FIG. 2, the ON DISP signal is the transistor Tr1.
When input to the base of, the base current flows through the transistor Tr1 and the transistor Tr1 is turned on.

When the transistor Tr1 is turned on, the bases of the transistors Tr2 and Tr4 become the reference voltage VSS, a base current flows through the bases of the transistors Tr2 and Tr4, and the transistor Tr1 is turned on.
2 and the transistor Tr4 are turned on.

When the transistor Tr2 is turned on, the logic voltage VDD is applied to the base of the transistor Tr3, and the base current flows through the base of the transistor Tr3.
The transistor Tr3 is turned on.

When turned on, the transistor Tr3 reduces the liquid crystal drive voltage -VEE by the internal resistance of the transistor Tr3 and supplies it as the liquid crystal drive voltage -VEE 'to the liquid crystal drive circuit 12 via the power supply line LE'. This liquid crystal drive voltage −
Due to VEE ′, electric charges having the potential of the liquid crystal drive voltage −VEE ′ are accumulated in the negative electrode of the capacitor C12.

When the transistor Tr4 is turned on, the logic voltage VDD is applied to the transistor Tr5, the transistor Tr5 is turned off without the base current flowing, and the circuit of the bleeder resistance Rf is opened.

That is, when the transistor Tr5 is turned off, the bleeder resistance Rf changes to the logic voltage VDD.
Is cut off from the power supply line LD for supplying the current to prevent current from flowing through the bleeder resistance Rf.

Therefore, when the liquid crystal drive circuit 12 is on, the flow of current to the bleeder resistor Rf is blocked, and the current consumption is reduced. As a result, this current control circuit 14
When the liquid crystal display device 10 provided with is driven by a battery, it can be driven for a longer time than in the past.

When the power source of the liquid crystal display device 10 is turned off, the CPU 13 causes the DIS 13 to turn off as shown in FIG.
The P signal is output to the current control circuit 14,
When the OFF DISP signal is input, the bleeder resistor Rf is connected to the power source line LE 'and the power source line LD so that the discharge current flows through the bleeder resistor Rf.

That is, the OFF DISP signal is a signal having the same level as the reference voltage VSS, and as shown in FIG. 2, when the OFF DISP signal is input to the base of the transistor Tr1, the transistor Tr1 has a low voltage. The base current is stopped and the transistor Tr1 is turned off.

When the transistor Tr1 is turned off, the base currents of the transistors Tr2 and Tr4 are stopped and the transistors Tr2 and Tr4 are turned off.

When the transistor Tr2 is turned off, the base current of the transistor Tr5 is stopped and the transistor Tr5 is turned off.
5 turns off.

When the transistor Tr5 is turned off, the potential of the power supply line LE 'drops and the supply of the liquid crystal drive voltage -VEE' to the liquid crystal drive circuit 12 is stopped. Then, when the transistor Tr5 is turned off, the power supply line LE 'is connected to the capacitors C12 and C1 when the transistor Tr5 is turned on.
A negative potential appears due to the charges accumulated in 3.

When the transistor Tr4 is turned off,
A base current flows through the transistor Tr5, turning on the transistor Tr5.

When the transistor Tr5 is turned on, the bleeder resistance Rf causes the power supply line LE 'and the power supply line LD.
Connected to the bleeder resistor Rf and transistor Tr
5, a closed circuit is formed between the capacitors C12 and C13, and the capacitors C12 and C13 are
As shown in FIG. 3, the electric charge accumulated in the current flows through the closed circuit as a discharge current If to the bleeder resistance Rf. The discharge time at this time is determined by the load impedance between the power supply line LE 'and the power supply line LD, the bleeder resistance Rf, and the time constants of the capacitors C12 and C13.

As described above, the charges accumulated in the capacitors C12 and C13 are bleeder resistance Rf.
It is possible to prevent the discharge current If from flowing as a discharge current If to be applied as a DC voltage to the liquid crystal display panel 11 via the liquid crystal drive circuit 12, and it is possible to prevent abnormal display or deterioration of the liquid crystal.

As described above, according to this embodiment, the capacitor C12 for liquid crystal protection is provided between the power supply lines for supplying power to the liquid crystal drive circuit 12 for driving the liquid crystal (between the power supply lines LD and LE '). , C13, a bleeder resistance Rf for inserting a discharge current If from the C13 is inserted. The bleeder resistance Rf is connected to the power supply line LD when the liquid crystal drive circuit 12 operates.
The liquid crystal drive circuit 12 is separated from the power supply line LE 'and is connected to the power supply line LD and the power supply line LE' when the operation of the liquid crystal drive circuit 12 is released. Therefore, the liquid crystal drive circuit 12 is driven while preventing abnormal display and deterioration of the liquid crystal. At times, it is possible to prevent a current from flowing through the bleeder resistor Rf, and it is possible to reduce power consumption. As a result, even if the liquid crystal display device is driven by a battery, it can be driven for a long time.

In the above embodiment, the DISP signal for controlling the operation of the liquid crystal drive circuit 12 disconnects the connection of the bleeder resistor Rf from the power supply line and switches the connection, but this is not the only option. Instead, the connection of the bleeder resistance Rf to the power supply line may be switched by turning on / off the power supply itself.

[0053]

According to the present invention, at the time of driving the liquid crystal drive circuit, it is possible to prevent the current from flowing through the resistor inserted to flow the discharge current from the liquid crystal protection capacitor, thereby reducing the power consumption. It can be reduced. As a result, the liquid crystal display device can be driven for a long time even when it is driven by a battery while preventing abnormal display and deterioration of the liquid crystal.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a liquid crystal display device to which an embodiment of a current control circuit of the present invention is applied.

FIG. 2 is a detailed circuit diagram of the current control circuit of FIG.

3 is a waveform diagram showing a current control operation of the current control circuit of FIG.

FIG. 4 is a schematic configuration diagram of a liquid crystal display device using a conventional current control circuit.

FIG. 5 is a waveform diagram showing the operation of the conventional current control circuit.

[Explanation of symbols]

 10 liquid crystal display device 11 liquid crystal display panel 12 liquid crystal drive circuit 13 CPU 14 current control circuit C10 to C13 electric field capacitors Tr1 to Tr5 transistors R1 to R9 resistors Rf breeder resistors

Claims (3)

[Claims] 1. A current control circuit of a liquid crystal display device in which a resistor for flowing a discharge current from a liquid crystal protection capacitor is inserted between power supply lines for supplying power to a liquid crystal drive circuit for driving liquid crystal, The liquid crystal drive circuit is provided with a switching means for disconnecting the connection between the power supply line and the resistor when the liquid crystal drive circuit is operating, and for connecting the power supply line and the resistor when the operation of the liquid crystal drive circuit is released. Current control circuit for display device. 2. The current control circuit for a liquid crystal display device according to claim 1, wherein the switching means performs the switching operation according to a signal from a control means for controlling the operation of the liquid crystal drive circuit. 3. The current control circuit for a liquid crystal display device according to claim 1, wherein the switching means performs the switching operation by turning on / off a power source to the liquid crystal drive circuit.