JPH01225995A - Power source controlling circuit for liquid crystal - Google Patents

Abstract

PURPOSE:To easily and inexpensively control the power source of liquid crystal by directly controlling the power source by using a reset signal. CONSTITUTION:When a fixed time elapses after a power switch is turned on, a reset signal 12 rises and transistors 8 and 21 and a negative-output-three- terminal regulator 19 are turned on. As a result, a power source 11 for driving liquid crystal outputs electric power. When the power switch is turned off thereafter, the reset signal 12 immediately falls and the power source 11 is turned off. Simultaneously, a transistor 20 is turned on and electric power is supplied to the line of the power source 11 from a logic power source 10. As a result, the power source 11 for driving liquid crystal is set to the same level as the logic power source 10. Therefore, the power source 11 falls as the logic power source 10 falls. Therefore, the power source of liquid crystal can be controlled easily and inexpensively.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a liquid crystal power supply control circuit.

[Prior Art] Usually, a liquid crystal driver is used to drive a liquid crystal panel. There are a logic power supply 31 and a liquid crystal driving power supply 32 as power supplies added to the liquid crystal driver. Power on/
To prevent latch-up of the LCD drive when turned off, the power supply startup and powerdown sequences are determined. The sequence is shown in FIG. As shown in this figure, when the logic power supply is turned off, the liquid crystal driving power supply must be at the same voltage level as the logic power supply, that is, VDD33.

Conventionally, in order to maintain this sequence, a signal indicating that the power switch was turned off was monitored, and when that signal was received, the power was turned on/off using software to control the logic power supply and the liquid crystal power supply. Ta.

[Problems to be Solved by the Invention] If the power source of a device using a liquid crystal display device is a normal Act source that does not have a battery or the like, there is no need to control the power source by software. Therefore, in the power supply control method using software, if the power source of the device is an AC power supply, one signal line, one output port for controlling the power supply, and software control are additionally required. Therefore, in order to solve these problems, the present invention aims to easily control the power supply by controlling the power supply using a circuit.

[Means for Solving the Problems] The liquid crystal power supply control circuit of the present invention is characterized in that it directly controls the power supply of the liquid crystal using a reset signal in a device using a liquid crystal as a display device.

[Operations] In the present invention, the power supply for driving the liquid crystal is controlled by a reset signal.

[Example] Hereinafter, the present invention will be explained in detail based on an example. FIG. 1 shows the sequence of the logic power supply 3, the liquid crystal driving power supply 4, and the reset signal 5.

Further, FIG. 2 shows an example of a power supply circuit including a liquid crystal power supply control circuit as one of the embodiments of the present invention.

This power supply includes a household AC 100V power supply 7, a liquid crystal backlight power supply 9, and a liquid crystal drive power supply 11 (DC-20V).
, generates a reset signal 12. Further, a logic power supply 10 (DC +5V) is generated from a liquid crystal backlight power supply 9 using a three-terminal regulator 6.

First, the power supply circuit will be briefly explained. This power supply consists of a switching transistor, an oscillation circuit, a voltage control circuit, etc.
This is a separately excited switching regulator that controls the power supply voltage on the secondary side by the power supply control circuit 12 on the next side, and is of a flyback type that outputs voltage on the secondary side when the switching transistor is off.

Next, detailed operations will be explained in comparison with the sequence shown in FIG. The liquid crystal backlight power supply 9 connects the secondary side transformer output 17 to a diode 13 and a capacitor 1.
4 and is made smooth. A logic power supply 10 (
It generates DC +5V). Its rising and falling edges form the waveform shown in 3 in FIG. The liquid crystal drive power supply 11 connects the secondary side transformer output 18 to the diode 1
5. A smoothed signal is generated by a capacitor 16 through a negative output three-terminal regulator 19. The reset signal 12 connects the voltage of the backlight power supply 9 of the liquid crystal to the resistor 23.
This is a signal generated by comparing the voltages obtained by dividing the voltages by 24 and 24 by a voltage comparison circuit 22 composed of an operational amplifier, a reference voltage, and the like. This reset signal is a power switch that is a signal that is turned on after a certain period of time after the logic power supply 3 is turned on, and turned off a certain period of time before the logic power supply 3 is turned off, as shown in 5 in Fig. 2. When the reset signal 12 is turned on and a certain period of time elapses, the reset signal 12 rises and the six transistors 8 are turned on. Then, the transistor 21 turns on and the negative output 3-terminal regulator 19
When turned on, the liquid crystal driving power source 11 is outputted.

Next, when the power switch is turned off, the reset signal 12 immediately falls, and the transistor 8, the transistor 21, and the negative output three-terminal regulator 19 are turned off one after another, thereby turning off the liquid crystal driving power supply 11. At the same time, the transistor 20 is turned on, power is supplied from the logic power supply 10 to the line of the liquid crystal drive power supply 11, and the liquid crystal drive power supply 11 becomes at the same level as the logic power supply 10. Thereafter, at the same time as the logic power supply 1o falls, the liquid crystal driving power supply 11 also falls.

In this way, the sequence of the liquid crystal power supply can be maintained.

[Effects of the Invention] The liquid crystal power supply control circuit of the present invention makes it possible to control the liquid crystal power supply in a simple and inexpensive manner.

[Brief explanation of the drawing]

Figure 3 is a diagram showing the conventional sequence of rising and falling of the logic power supply and the liquid crystal power supply. Figure 1 shows
A diagram showing the rise and fall sequences of a logic power supply, a liquid crystal drive power supply, and a reset signal. FIG. 2 is a diagram showing an example of a simple power supply circuit including an example of the power supply control circuit of the present invention. 3...Logic power supply 4...Liquid crystal drive power supply 5...Reset signal and above Applicant Seiko Epson Co., Ltd. Agent Tsutomu Mogami, patent attorney, and 1 other person Figure 1

Claims (1)

[Claims] 1. A liquid crystal power control circuit for use in a device using a liquid crystal as a display device, characterized by having a power supply circuit for driving the liquid crystal controlled by a reset signal.