JPH02150819A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To use an optical amplifier which is small in rated power consumption by connecting resistances to the outputs of operational amplifiers in series and then connecting smoothing capacitors. CONSTITUTION:Intermediate levels V1', V2'... Vn' are extracted by resistance division between two kinds of power sources VDD and VEE which differ in voltage value and operational amplifiers OP1 - OP4 are connected to the intermediate levels to obtain low-impedance intermediate levels V1, V2... Vn, thereby driving liquid crystal. Then resistances R8 - R11 are connected to the outputs of the operational amplifiers OP1 - OP4 in series and the smoothing capacitors C1 - C4 are connected. Therefore, the output currents of the operational amplifiers R8 - R11 can be limited by the resistances R8 - R11. For variation of a liquid crystal driving power source due to the current limiting resistances R8 - R11, the values of the smoothing capacitors C1 - C4 are increased to stabilize the variation. Consequently, the operational amplifiers which are small in rated power consumption are usable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device, particularly a large capacity liquid crystal display device.

[Conventional technology]

A liquid crystal drive power supply circuit shown in FIG. 7 has been used in a conventional liquid crystal display device. In the same figure, five voltage dividing resistors R1,
R2, R3, R4, R5 are connected in series and Vl', V2
', V3'', and ■4' are generated.The liquid crystal drive power supply vo, which is necessary for time-division driving of the liquid crystal display device, is generated.
vi, v2, V3. V4. V5 is VDD, VEE
and vi'V2°, V3', V4°, respectively, through operational amplifiers OPI, OP2. OP3. This is obtained by lowering the impedance with OF2. Capacitor C1, C2
, C3, and C4 are inserted to suppress fluctuations in the liquid crystal drive power supplies v1 to V4.

[Problem to be solved by the invention]

However, in the liquid crystal drive power supply circuit configured in this way, the current flowing through each power supply increases due to the larger screen size and higher duty of the liquid crystal display device, so it is necessary to use an operational amplifier with a large rated power consumption. Ta. However, since operational amplifiers with high rated power consumption have a large external size and are expensive, there has been a problem that the liquid crystal display device has a large external size and is also expensive.

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned problems, and an object of the present invention is to provide a liquid crystal display device that can use an operational amplifier with a low rated power consumption.

[Means to solve the problem]

The liquid crystal display device of the present invention uses two types of power supplies (
VDD, VEE) by dividing the resistance between them to create multiple intermediate levels V
l', V2°, . ..., a liquid crystal display device that drives a liquid crystal by obtaining Vn, characterized in that a resistor is connected in series to the output of the operational amplifier, and a smoothing capacitor is connected thereafter.

〔Example〕

FIG. 1 is a driving power supply circuit diagram of a liquid crystal display device according to a first embodiment of the present invention. The same parts as those in FIG. OP
3. Resistors R8 to R11 are connected to the output of OF2. Since the output current of the operational amplifier can be limited by a resistor,
It is possible to avoid exceeding the power rating of the operational amplifier. By increasing the values of the smoothing capacitors 01 to C4, it is possible to stabilize the liquid crystal drive power supply more stably than the conventional liquid crystal drive power supply with respect to fluctuations in the liquid crystal drive power supply due to the insertion of the current limiting resistor.

Using a 12-inch 640 x 40 dot liquid crystal display device, the values of resistors R8 to R11 were 4.7Ω.

The results of an experiment in which the values of 01 to C4 were changed from the conventional 1 μF to 22 μF showed that OPI, OF2. The total power consumption of the OF2 and OF2 operational amplifiers was able to be reduced from the conventional 400 mW to 200 mW. In addition, by increasing the value of the smoothing capacitor, fluctuations in the liquid crystal drive power supply that occur when the selected line of a liquid crystal display device that is driven line-sequentially is switched can be reduced to 0. I was able to reduce it to 2v or less.

FIG. 2 shows an embodiment in which the outputs of operational amplifiers are used as the liquid crystal drive power supplies VO and V5. In the embodiment of FIG. 1, Vl,
Used when the voltage of V4 exceeds the maximum output voltage rating of the operational amplifier.

3 and 4 are drive power supply circuit diagrams of a liquid crystal display device showing a second embodiment of the present invention. The difference from the first embodiment is that the circuit is inserted after the current limiting resistor of the operational amplifier. This is how to insert a smoothing capacitor. The driving power supply for a liquid crystal display device used at high duty is the voltage between V2 and V3 (1
) VO-Vl, Vl-V2. V3-V4. V4-V
Use the voltage much higher than the voltage between 5 and 5. 1/10
In the case of 0 duty, the voltage between V2 and V3 is used at a voltage seven times higher than the voltage between other power supplies. 1/200
In the case of duty, it is 11 times. Therefore, the method of inserting the smoothing capacitor shown in FIGS. 3 and 4 can lower the withstand voltage of the smoothing capacitor than the method of inserting the smoothing capacitor shown in FIGS. 1 and 26. Comparing the breakdown voltage of the 04 smoothing capacitor, it is 1/200
For Dut V, the voltage between VO and V5 is required to be about 25V, and the voltage between V2 and V3 is 1 of the voltage between the main power supply.
1x is optimal. Therefore, the voltage applied to smoothing capacitor C4 in FIG. 1 of the first embodiment is 23.3V, and the voltage applied to C4 in FIG. 3 of the second embodiment is 1.7V. The actual withstand voltage of the capacitor is 35V, with a little margin.
, 6°3V is used.

5 and 6 are drive power supply circuit diagrams of a liquid crystal display device showing a third embodiment of the present invention, which differs from the first and second embodiments in the way in which smoothing capacitors are inserted. This method requires a higher breakdown voltage of the smoothing capacitor than the second embodiment, but it requires a lower breakdown voltage than the first embodiment. For example, the voltage applied to capacitor C4 in Fig. 5 is Calculated under the above conditions at 1/200Duty: 3.3
V, and the withstand voltage of the capacitor is 6.3 after taking a little time.
Use v.

In the third embodiment, since a smoothing capacitor is connected to a power source with low impedance, fluctuations in the liquid crystal driving power source can be made smaller than in the second embodiment. 12 inch 640x400
Using a dot liquid crystal display device, the values of the resistances R8 to R11 of the liquid crystal drive power supply circuit shown in FIGS. 3 and 5 are set to 4□7Ω,
According to the results of an experiment with the value of C1 to C4 set to 22 μF, the transient voltage fluctuation value in FIG. 3 of the second embodiment is 250 mV, and the transient voltage fluctuation value in FIG. 5 of the third embodiment is 200 mV.
Met.

〔Effect of the invention〕

As explained above, according to the present invention, the operational amplifier used for the liquid crystal drive power supply required for the liquid crystal display device can be one with a low rated power consumption, so it is possible to provide a small and inexpensive liquid crystal display device. Has excellent effects.

[Brief explanation of the drawing]

1 and 2 are liquid crystal drive power supply circuit diagrams of a liquid crystal display device according to a first embodiment of the present invention, and FIGS. 3 and 4 are diagrams of a second embodiment of the present invention.
Liquid crystal drive 7i of the liquid crystal display device of the embodiment! 5 and 6 are liquid crystal drive power supply circuit diagrams of a liquid crystal display device according to a third embodiment of the present invention, and FIG. 7 is a liquid crystal drive power supply circuit diagram of a conventional liquid crystal display device. R1-R7...Voltage dividing resistor R8-R13...Current limiting resistor OPI~OP6...Operation amplifier 01~C6...Smoothing capacitor or more Applicant: Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki 1 person Figure 1 Figure 2 Figure Figure

Claims (3)

[Claims] (1) Two types of power supplies with different voltage values (VDD, VEE)
A plurality of intermediate levels V1', V2',...
, Vn' and connect operational amplifiers to each intermediate level to create low impedance intermediate levels V1, V2, ..., V
1. A liquid crystal display device that drives a liquid crystal by obtaining n, characterized in that a resistor is connected in series to the output of the operational amplifier, and a smoothing capacitor is connected thereafter. (2) If VDD>V1>…>Vn>VEE, the smoothing capacitor is connected between VDD and V1, between V1 and V2, and V
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is arranged between intermediate levels between n_-_1 and Vn and between Vn and VEE. (3) If VDD>V1>...>Vn>VEE, then V1~
2. The liquid crystal display device according to claim 1, wherein the smoothing capacitor is inserted between Vn/2 and VDD and between V(n/2)+1 and VEE.