JPH04366892A - Liquid crystal driver protecting circuit - Google Patents

Abstract

PURPOSE:To prevent a liquid crystal driver (LCD) from being destructed by constituting this LCD protecting circuit of the 1st transistor(TR) for detecting a logic power supply and the 2nd TR for switching LCD power supply, and when no logic power supply is impressed, turning an LCD selecting voltage to ground potential. CONSTITUTION:When logic power supply VDD is not impressed, current can not flow into the base of the 1st TR 3 through a resistor R1, so that the collector of the 1st TR 3 is turned to high impedance and the collector of the 2nd TR 4 is turned to a ground voltage. Since the collector of the 2nd TR 4 is connected to an intermediate point between a resistor R4 and a variable resistor VR1, the base potential of a TR3 is turned to the ground voltage, its emitter is also turned to the ground voltage and LCD selecting voltage VDDR is turned to the ground voltage. When the logic voltage VDD is impressed, the voltage VDDR is divided by the resistors R4, R5 and the variable resistor VR1 and a correct voltage is supplied.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driver protection circuit for a liquid crystal drive power supply for driving a simple matrix type liquid crystal display panel.

0002

2. Description of the Related Art In recent years, flat panel displays using liquid crystals have been actively developed. Display capacity continues to increase, and simple matrix type liquid crystal display panels driven by 1/480 duty have become commonplace. As the duty becomes higher, the liquid crystal drive voltage also increases.
Liquid crystal drivers with 0V breakdown voltage have now appeared. A high-voltage liquid crystal driver may be destroyed if a liquid crystal driving power is applied without applying a logic power. For this reason, it is desirable that the logic power source and the liquid crystal drive power source be applied at the same time; however, conventionally used liquid crystal drive power sources have been independent of the logic power source. (However, this excludes those generated by boosting the liquid crystal drive power supply from the logic power supply.) For this reason, the liquid crystal drive power supply was configured to be able to be turned on and off independently of the logic power supply of the liquid crystal driver.

0003

[Problems to be Solved by the Invention] However, the liquid crystal drive power supply for driving a conventional simple matrix type liquid crystal display panel has a configuration that can be turned on and off independently of the logic power supply of the liquid crystal driver, so the logic power supply is not applied. However, there is a problem in that the liquid crystal driver can be turned on without having to do so, and as a result, the liquid crystal driver is destroyed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve this conventional problem by lowering the liquid crystal drive power supply to the ground potential when the logic power supply is not applied to prevent the liquid crystal display driver from being destroyed. The solution is to provide a protective circuit to the liquid crystal drive power supply.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the present invention detects the logic voltage when the logic power of the liquid crystal driver is not applied even though the liquid crystal drive power is applied. However, if a logic voltage is not generated, a liquid crystal driver protection circuit that lowers the liquid crystal drive power supply to the ground potential is provided in the liquid crystal drive power supply, thereby making it possible to prevent the liquid crystal display driver from being destroyed.

[0006]

[Operation] The liquid crystal driver protection circuit configured as described above drops the liquid crystal drive power supply to the ground potential when the logic power supply for the liquid crystal driver is not applied, and lowers the liquid crystal drive power supply from the ground potential when it is applied correctly. It is released and generates a predetermined liquid crystal driving power. In this way, the liquid crystal driver is prevented from being destroyed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. FIG. 1 is an embodiment of a liquid crystal driver protection circuit diagram according to the present invention. In FIG. 1, 1 is a liquid crystal driver protection circuit, and the liquid crystal drive power supply VLCD is connected to resistors R4 and R5.
and the voltage is divided by the variable resistor VR1, and the transistor TR
Supplied on the base of 3. The emitter of the transistor TR3 becomes a liquid crystal drive selection voltage VDDH, which is supplied to the liquid crystal driver (not shown) and the voltage follower circuit 2. The voltage follower circuit 2 supplies a bias power supply with low impedance to the liquid crystal driver, and V1 and V4 are supplied as non-selection voltages for the scan driver IC, and V2 and V4 are supplied as non-selection voltages for the signal driver IC. In addition, each voltage value is the liquid crystal drive selection voltage VD
It is obtained by dividing the voltage between DH and ground voltage GND using resistors R6 to R10. By varying the variable resistor VR1, the level of the liquid crystal drive selection voltage VDDH is changed, and the contrast of the liquid crystal display panel can be adjusted.

The logic power supply VDD is connected to a resistor R1 of the liquid crystal driver protection circuit 1. Here, it is assumed that the logic power supply VDD is not applied even though the liquid crystal drive power supply VLCD is applied. Since the prescribed voltage is not generated in the logic power supply VDD, no current is input to the base of the first transistor 3 through the resistor R1, so the collector of the first transistor becomes high impedance, and the current flowing through the resistor R3 is reduced. is input to the base of the second transistor 4, so the collector of the second transistor becomes approximately ground voltage.

Since the collector of the second transistor 3 is connected to the midpoint between the resistor R4 and the variable resistor VR1, the base potential of the transistor TR3 becomes the ground voltage. As a result, the emitter of the transistor TR3 also becomes the ground voltage, so the liquid crystal drive selection voltage VDDH becomes the ground voltage. On the other hand, when the logic power supply VDD is applied, the first transistor 3 is turned on and the second transistor 4 is turned off, and the liquid crystal drive selection voltage VDDH is applied to the resistors R4 and R5.
, the correct voltage divided by the variable resistor VR1 is supplied.

As described above, if the logic power is not applied even though the liquid crystal driving power is applied,
Since the liquid crystal drive selection voltage applied to the liquid crystal driver becomes the ground voltage, destruction of the liquid crystal driver can be prevented.

[0011]

Effects of the Invention As explained above, the present invention solves the problem that the liquid crystal driver is destroyed because the logic power is not applied even though the liquid crystal drive power is applied, and the problem is that the liquid crystal driver is destroyed. It can be added to the power supply circuit, and can be used to protect liquid crystal drivers such as liquid crystal display modules.

[Brief explanation of drawings]

FIG. 1 is a diagram of a liquid crystal driver protection circuit of a liquid crystal driving power supply according to the present invention.

[Explanation of symbols]

1. LCD driver protection circuit 2 Voltage follower circuit 3 First transistor 4 Second transistor

Claims (1)

[Claims] [Claim 1] In a liquid crystal drive power supply for driving a simple matrix type liquid crystal display panel, a collector that has a ground potential when a logic voltage is applied to the liquid crystal driver and has a high impedance when not applied. A first transistor has an output terminal, and the collector output terminal of the first transistor is a base input terminal, and when the collector output terminal of the first transistor is at ground potential, it becomes high impedance. It consists of a second transistor with a collector output terminal that is at ground potential when the collector output terminal is high impedance, and when the logic voltage is not applied even though the liquid crystal voltage is applied to the liquid crystal driver. , a liquid crystal driver protection circuit that forcibly sets the liquid crystal voltage to ground potential to prevent the liquid crystal driver from being destroyed.