JPH09197371A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mitigate measures against heat and to make the frame of the device narrow by supplying a high and a low source voltage to buffers connected to the high-potential and low-potential sides of a resistance dividing circuit. SOLUTION: A power source part 31 outputs 1st and 2nd source voltages Vo1 and Vo2 as plural source voltages. Further, the resistance dividing circuit 32 is constituted by connecting resistances R1-R4 in series so as to prescribe plural bias voltages VH, VSH, VD, HV, DL, VSL, and VL for a select voltage and a nonselect voltage, and both its terminals are connected between the power source terminal Vo1 of the power source part 31 and a ground terminal Vss. Power supply to the buffers B1 and B2 of a buffer circuit 33 for high nonselect voltages VSH and VDH on a scanning side and a signal side is performed with a high voltage by a 1st source voltage Vo1 terminal and a ground terminal Vss (1st power source) and power supply to buffers B3 and B4 for low nonselect voltages VSL and VDL on the scanning side and signal side is performed with a low voltage by the 2nd source voltage Vo2 and ground terminal Vss (2nd power source).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a dot matrix type liquid crystal cell.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Laid-Open No. 5-19232, in a liquid crystal display device having a dot matrix type liquid crystal cell, a liquid crystal driving circuit having a scanning circuit and a signal circuit is connected to the liquid crystal cell, A bias voltage is supplied to this circuit to drive the liquid crystal cell using the voltage averaging method.

Conventionally, a power supply circuit in a liquid crystal display device of this type is provided with a resistance division circuit at a power supply terminal Vo in order to apply a selection and non-selection bias voltage to a liquid crystal drive circuit 2 as shown in FIG. 2, for example. The connection is made and the voltage at the division point is taken out via the buffers B1 to B4. Power is supplied to each buffer by a single power supply using the power supply terminal Vo and the ground terminal Vss.

[0004]

However, according to the above-mentioned conventional power supply circuit configuration, the power saving is not sufficiently achieved, so that the load accompanying the recent demand for high definition and large screen of the liquid crystal display device. Although it is necessary to take sufficient heat countermeasures in response to the increase, it is difficult to take sufficient heat countermeasures against an increase in load due to the demand for a narrower frame and thinner device. Therefore, it is a main object of the present invention to provide a liquid crystal display device capable of reducing heat countermeasures and making the device narrower in frame and thinner.

[0005]

According to the present invention, there is provided a liquid crystal cell having a plurality of electrodes intersecting each other with a liquid crystal layer interposed therebetween, a scanning circuit connected to one electrode group of the liquid crystal cell, and the other of the liquid crystal cells. A liquid crystal drive circuit comprising a signal circuit connected to the electrode group of, and a power supply circuit for supplying a driving power supply and a selection voltage and a non-selection voltage to the liquid crystal drive circuit, wherein the power supply circuit is A resistance division circuit that defines a selection voltage and a non-selection voltage, a buffer circuit including a plurality of buffers connected to division points of the resistance division circuit, and a high potential side of the resistance division circuit with respect to the buffer circuit The buffer is provided with a high voltage, and a power supply unit for supplying a low voltage power to the buffer connected to the low potential side of the resistance division circuit.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a liquid crystal display device according to an embodiment of the present invention. In this figure, reference numeral 1 denotes a liquid crystal cell having a plurality of electrodes that intersect each other with a liquid crystal layer interposed therebetween, that is, a liquid crystal cell having a scanning electrode group and a signal electrode group.
It is composed of a super twist type field effect liquid crystal cell twisted by 0 to 260 degrees. Reference numeral 2 denotes a scanning circuit connected to a scanning electrode group, which is one electrode group of the liquid crystal cell 1, and the liquid crystal cell 1.
In the liquid crystal drive circuit including a signal circuit connected to the signal electrode group which is the other electrode group, the scanning circuit and the signal circuit are configured by a plurality of drive ICs. A clock signal, a timing signal, a data signal, or the like is given to the liquid crystal drive circuit 2, and the liquid crystal cell 1 is driven based on the voltage averaging method.

Reference numeral 3 denotes a liquid crystal driving circuit 2 which supplies a driving power source V.
EE, a power supply circuit that supplies a selection voltage and a non-selection voltage, a power supply unit 31 that supplies a plurality of power supply voltages, and a plurality of bias voltages (VH, VS) for the selection voltage and the non-selection voltage.
H, VDH, VDL, VSL, VL) and a buffer circuit 33 including a plurality of buffers B1 to B4 connected to the resistance dividing points.

The power supply unit 31 is composed of, for example, a DC-DC converter that outputs the first and second two power supply voltages Vo1 and Vo2 as a plurality of power supply voltages, but other circuit configurations may be used. . The first power supply voltage Vo1 is
Bias voltage V that regulates the high selection voltage on the scanning side and the signal side
In addition to being used as H, it is used as a driving power supply VEE for the liquid crystal driving circuit 2 and a driving power supply for the high potential side buffers B1 and B2. The second power supply voltage Vo2 is used as a power supply for driving the buffers B3 and B4 connected to the connection point on the lower potential side than the intermediate potential of the resistance division circuit 32.

The resistance division circuit 32 includes a plurality of bias voltages (VH, VSH, VDH, VD) for the selection voltage and the non-selection voltage.
L, VSL, VL), resistors R1 to R5 are connected in series so as to define the power supply terminal Vo1 of the power supply unit 31.
And the ground terminal Vss. In this example, the values of the resistors R1 to R5 are R1 = R2 = R4 = R5 =
r and R3 = (n−4) · r are set. Where n
Indicates a bias ratio determined by the number of scanning lines. And
Bias voltage VH is a high selection voltage on the scanning side and signal side, voltage VSH is a high non-selection voltage on the scanning side, voltage VDH is a high non-selection voltage on the signal side, voltage VDL is a low non-selection voltage on the signal side, and VSL is a scan. The low non-selection voltage on the side, VL is used as the low selection voltage on the scanning side and the signal side.

The buffers B1 to B4 are operational amplifiers (opamps) or the like respectively connected to the connection points of the resistors R1 to R5 so as to supply power to the liquid crystal drive circuit 2 at a voltage defined by resistance division. Buffers B1 and B for high non-selection voltages VSH and VDH on the scanning side and the signal side
Power is supplied to 2 at a high voltage by the first power supply voltage Vo1 terminal and the ground terminal Vss (first power supply), and the low non-selection voltages VSL and VDL buffers B3 and B4 on the scanning side and the signal side are supplied.
The power supply to the second power supply voltage Vo2 terminal and the ground terminal Vss (second power supply) is performed at a low voltage.

Here, for example, an SVGA type STN having 300 scanning lines is used as the liquid crystal cell 1, and the liquid crystal drive circuit 2 is used.
It is assumed that the high selection voltage VH and the power supply voltage VEE are set to 30 volts. The power supply unit 31 sets the first power supply voltage Vo1 to 30 V corresponding to the liquid crystal cell 1, and adds the second power supply voltage Vo2 to the signal side low non-selection voltage VDL by a predetermined voltage value ΔV. Value more than the value (Vo2 ≧ VDL + Δ
V) is set. Here, the low non-selection voltage V on the signal side
DL is calculated as 3.33 V (in the case of n = 18) based on the voltage division ratio (2 / n) of the resistance division circuit 32, and Δ
V is a voltage drop value between the power supply and the output of the buffer B3 and is generally about 1.5 V. Therefore, the second power supply voltage Vo2 is
For example, it is set to 4.85 volts or more, which is 4.83 volts or more.

With this structure, the two buffers B3 and B4 on the low potential side, which have been conventionally operated by receiving the supply of the high voltage power source VEE, are driven at a low voltage by the second power source voltage Vo2. It is possible to reduce the power consumption.

Therefore, the power supply circuit system (mainly the liquid crystal drive circuit 2
And the approximate power consumption W of the buffer circuit 33) will be determined. Here, the total current flowing in the liquid crystal drive circuit 2 through the supply path of the power supply voltage VEE is IEE, the total current flowing in the buffers B1 and B2 is IBH, the total current flowing in the buffers B3 and B4 is IBL, and their total is When the current is I, the ratio of IEE, IBH and IBL is generally 4:
Since it is about 3: 3, IEE = 0.4I, IBH = IBL =
It can be represented as 0.3I. Therefore, the power consumption W is
Power consumption W1 [30 · (0.4I + 0.3I)] related to the first power supply voltage Vo1 (30 V) of the power supply unit 31 and power consumption W2 [4 related to the second power supply voltage Vo2 (4.85 V). 0.85 · 0.3I], and the power consumption W including W1 and W2 is about 22.5.
I. As a comparative example, when the power consumption W0 of the conventional circuit shown in FIG. 2 is calculated under the same conditions, W0 is 3
Since it is 0I, it can be understood that according to the embodiment shown in FIG. 1, the power consumption of the power supply circuit system can be reduced by 25% as compared with the conventional example.

As described above, since the power consumption of the power supply circuit system can be greatly reduced, the amount of heat generation can be reduced and the countermeasures against heat can be reduced, and at the same time, the parts constituting the power supply circuit 3, for example, the power supply. The components such as the DC-DC converter configuring the unit 31 and the operational amplifier (operational amplifier) configuring the buffer circuit 33 can be downsized by using components with low allowable loss, and the device can be made thin and narrow. It can contribute to making a frame.

Further, the second power supply voltage Vo2 is used only as a power supply source, and even if the voltage slightly fluctuates, there is little trouble. Therefore, when a DC-DC converter is used for the power supply unit 31, the transformer thereof is used. It is also possible to directly use the output to supply the power supply voltage Vo2. With such a configuration, the circuit for stabilizing the voltage Vo2 can be simplified or omitted to simplify the circuit configuration and reduce the size. It is possible to use a DC-DC converter that has been designed.

[0016]

As described above, according to the liquid crystal display device of the present invention, the power consumption of the power supply circuit system can be reduced, the countermeasures against heat can be reduced, and the structure of the power supply circuit system can be reduced. It is possible to reduce the size of parts and to reduce the thickness of the device and narrow the frame. When a DC-DC converter is used for the power supply unit, the transformer output can be directly used to supply a low-voltage power supply,
According to this structure, it is possible to use a DC-DC converter having a simplified circuit structure and a reduced size.

[Brief description of drawings]

FIG. 1 is a schematic view of a liquid crystal display device showing an embodiment of the present invention.

FIG. 2 is a schematic view of a conventional liquid crystal display device.

[Explanation of symbols]

 1 Liquid Crystal Cell 2 Liquid Crystal Driving Circuit 3 Power Supply Circuit 31 Power Supply Section 32 Dividing Resistor Circuit 33 Buffer Circuit

Claims (1)

[Claims] 1. A liquid crystal cell having a plurality of electrodes intersecting each other with a liquid crystal layer interposed therebetween, a scanning circuit connected to one electrode group of the liquid crystal cell, and a signal circuit connected to the other electrode group of the liquid crystal cell. In a liquid crystal display device comprising a liquid crystal drive circuit consisting of: and a power supply circuit for driving the liquid crystal drive circuit and supplying a selection voltage and a non-selection voltage, the power supply circuit defines the selection voltage and the non-selection voltage. A resistor divider circuit, a buffer circuit including a plurality of buffers connected to the dividing points of the resistor divider circuit, a high voltage to the buffer connected to the high potential side of the resistor divider circuit with respect to the buffer circuit, and the resistor divider circuit. A liquid crystal display device, comprising: a buffer connected to the low potential side of the circuit; and a power supply unit for supplying a low voltage power supply.