CN1135521C

CN1135521C - Electronic power circuit for liquid crystal

Info

Publication number: CN1135521C
Application number: CNB001330179A
Authority: CN
Inventors: 下田贞之
Original assignee: Seiko Instruments Inc
Current assignee: Seiko Instruments Inc
Priority date: 1999-10-21
Filing date: 2000-10-21
Publication date: 2004-01-21
Anticipated expiration: 2020-10-21
Also published as: CN1298170A; TW507097B; JP2001117068A

Abstract

There is provided a power supply circuit in which, with respect to common side drive voltages VH, VL, and V1 and segment side voltages V2 and V1, the relation of VH-V1=V1-VL is realized with high precision, and the relation of V2-V1=V1-Vss is realized with high precision. The segment side voltage V2 is halved by two resistors to generate the voltage V1. At this time, either one of the two resistors is trimmed, so that V2-V1 V1-Vss, which is caused by an offset voltage of a buffer circuit constituted by an operational amplifier and ratio precision fluctuation of the two resistors, is corrected, and the relation of V2-V1=V1-Vss is realized with high precision. Besides, a positive power supply of the buffer circuit constituted by the operational amplifier is adopted from the segment side voltage V2, so that the power loss of the buffer circuit constituted by the operational amplifier can be suppressed to (V2-V1)*(consumed current of liquid crystal panel).

Description

The power circuit of liquid crystal

The present invention relates to a kind of for the power circuit that drives LCD.

As everybody knows, can be used as the power circuit of general driving LCD as shown in Figure 3 with the power circuit of switching regulaor generation public side driving voltage.In other words, produce the positive-negative power that the public side driving voltage needs with switching regulaor 300 and transformer 301.In addition, from this public side driving voltage, produce the section side driving voltage with a resistor and an operational amplifier.

In adopting the LCD of multiplex addressing (MLA) driving method (as shown in Figure 3) for example, as the VH of public side driving voltage, the voltage relationship of VL and V1 must satisfy the relation of VH-V1=V1-VL.In addition, from this public side driving voltage VH, by with resistor 302,303 and 304 and

operational amplifier

305 and 306 dividing potential drops produce section side voltage V2 and V1 (voltage V1 is the public voltage of public side and section side).At this moment, V2, V1 and VSS must satisfy V2-V1=V1-VSS as the voltage relationship of section side driving voltage.Under the situation that does not satisfy these two relational expressions, the magnitude of voltage that each frame period is added to liquid crystal does not wait, and produces the phenomenon of for example streaking and so on thus, thereby display quality is descended.

Yet, in general power circuit, owing to be difficult to make transformer 301 to reach accurate winding ratio, thereby be difficult to satisfy the requirement of above-mentioned relation formula, can not highly precisely reach the requirement of VH-V1=V1-VL.

In addition, aspect the section side driving voltage, 302,303 and 304 couples of voltage VH carry out dividing potential drop with three resistors, are input to the buffer circuit that adopts

operational amplifier

305 and 306, use thereby will export as voltage V2 and V1.Yet, at this moment mainly contain the relation that two factors hinder V2-V1=V1-VSS.

A factor is the degree of accuracy of three resistors 302,303 and 304 resistance value ratios, and another factor is the offset voltage of operational amplifier 305 and 306.With regard to the degree of accuracy of three resistor resistance value ratios, if be avoidable with resistor adjusts in three resistors.As for the offset voltage of

operational amplifier

305 and 306, then must adopt and to regulate operational amplifier or the extremely low operational amplifier of offset voltage that departs from situation.These operational amplifiers are normally very expensive, and are difficult to get.Therefore, in conventional method, can not only spend but also highly precisely export this relation of V2-V1=V1-VSS less.

In addition, as following be about to speak of, also from the angle of power consumption, conventional method has such problem, though section side driving voltage V1 and V2 produce from resistance voltage VH being carried out dividing potential drop, at this moment is reduction resistor 302, the reactive current at 303 and 304 places, resistance has improved.

Like this, when these voltages really were added on the liquid crystal panel, need establish an amplification coefficient between voltage grading resistor and liquid crystal panel was the buffer circuit of 1 employing fortune from amplifier.

As the positive supply of operational amplifier, must use the voltage that is higher than the operational amplifier output voltage.At this moment, this positive voltage has become a loss of this power circuit with the pressure reduction between the operational amplifier output voltage.When the value of this voltage difference was big, it is big that loss becomes, and is difficult to reach the requirement of the little LCD of power consumption.

For addressing these problems, power circuit of the present invention divides half with two resistors with section side voltage, produces voltage V1.At this moment, thus any of two resistors through adjusting the offset voltage proofreaied and correct the buffer circuit that operational amplifier constitutes and V2-V1 that the fluctuation of two resistor ratios degree of accuracy causes, V1-VSS, thus highly precisely reach V2-V1=V1-VSS.

In addition, select the positive supply of section side voltage V2 for use, thereby the power loss of the buffer circuit that operational amplifier can be constituted is suppressed to (V2-V1) * (liquid crystal panel consumed current) as the buffer circuit of operational amplifier formation.

In the present invention, when adopting the buffer circuit of operational amplifier to produce the public bias voltage V1 of public side and section side, electric resistance partial pressure produces voltage as section side voltage from voltage V2, draws voltage V1 in the buffer circuit that this voltage input operational amplifier constitutes.At this moment, the positive supply of circuit provides as section side voltage from voltage V2 in the buffering of operational amplifier formation.

In the accompanying drawing:

Fig. 1 is the synoptic diagram of the power circuit of explanation one embodiment of the invention;

Fig. 2 is the synoptic diagram of explanation public side and section side driving voltage;

Fig. 3 is the synoptic diagram of the general power circuit of explanation;

Fig. 4 is the detailed maps of a square frame in the power circuit of key diagram 1.

Fig. 1 is the power circuit of the liquid crystal of one embodiment of the invention, and Fig. 4 is the detailed maps of Fig. 1 switching regulaor square frame.Common elements among Fig. 1 and Fig. 4 is with common symbolic representation.

Booster switcher regulator 101 and change type switching regulaor 102 produce voltage VH and VL respectively, as shown in Figure 2.The first booster switcher regulator 101 is made of FET105, error amplifier 106, control circuit 107, reference voltage 108 and feedback resistor 109 and 110 as shown in Figure 4, and constitutes the breaker type switching regulaor that boosts together with telefault 103 and the diode 104 as outer member.Change type switching regulaor 102 is made of error amplifier 114 and control circuit 115, and constitutes a conversion breaker type switching regulaor with FET111, diode 112, telefault 113 and feedback resistor 116 and 117 as outer member.Voltage VH is by voltage grading resistor 121 and 127 dividing potential drops, thereby by the voltage V2 of the tie point generation Fig. 2 that forms by buffer circuit 122 between voltage grading resistor 121 and 127.In addition, voltage V2 is also in the positive supply 128 of input operational amplifier 120.

Among Fig. 1, in the buffer circuit 120 that the voltage input operational amplifier at voltage grading resistor 118 and 119 tie point place constitutes.Getting this output voltage is V1.The positive supply 123 of buffer circuit 122 supplies from the output voltage V out2 of the second booster switcher regulator 124.This second booster switcher regulator 124 identical with the first booster switcher regulator 101, but providing what come from the tie point of voltage grading resistor 121 and 127 is the reference voltage V ref2 of the second booster switcher regulator 124, rather than the reference voltage among Fig. 4 108, and feedback resistor is made of resistor 125 and 126.

Subsequent, the course of work of circuit shown in Fig. 1 and Fig. 4 once is described.The voltage VH that the first booster switcher regulator 101 produces determines that according to the magnitude of voltage Vref of reference voltage 108, the resistance value R1 of feedback resistor 109 and the resistance value R2 of feedback resistor 110 this available (1) formula is represented:

VH＝Vref·(R1+R2)/R2 (1)

Voltage V2 determines available (2) formula table according to the resistance value R7 of voltage grading resistor 121 and the resistance value R10 of voltage grading resistor 127:

V2＝VH·R10/(R10+R7) (2)

Because the impedance transformation that voltage V1 passes through buffer circuit 120 as shown in fig. 1, and the positive side of same voltage V1 error originated from input amplifier 114, thereby owing to a termination voltage VH of feedback resistor 116 can obtain the voltage VL of change type switching regulaor generation with (3) formula:

VL＝-(VH-V1)·R4/R3+V1 (3)

Here, R3 represents the resistance of feedback resistor 116, and R4 represents the resistance of feedback resistor 117.If make R3=R4 by for example regulating, then voltage VL can be changed into-VH+2VL. in other words, can highly precisely satisfy the relation of VH-V1=V1-VL.

Subsequent, among Fig. 1, the reference voltage of the second booster switcher regulator 124 is next from the tie point confession of voltage grading resistor 121 and 127, thereby reference voltage V ref2 becomes the voltage of (4) formula:

Vref2＝VH·R10/(R10+R7) (4)

The output of the second booster switcher regulator 124, promptly the magnitude of voltage of operational amplifier 122 positive supplies 123 becomes the magnitude of voltage shown in (5) formula:

V123＝Vref2·(R8+R9)/R9 (5)

Here, voltage grading resistor 125 and 126 is in order to determining voltage Vout2, with the function class of the voltage grading resistor 109 of Fig. 4 and 110 seemingly.Equal Vref2 because amplification coefficient is the output voltage of 1 buffer circuit 122, thereby (5) formula becomes (6) formula:

V123＝V2·(R8+R9)/R9 (6)

In other words, voltage V123 is that voltage V2 is multiplied by (R8+R9)/R9 and draws.

The voltage V2 that buffer circuit 122 produces is as section side voltage, and this voltage is by resistor 118 (R5) and 119 (R6) dividing potential drop, in the input buffer circuit 120 simultaneously.Yet,, thereby differ and satisfy the relation of V2-V1=V1-VSS surely in view of buffer circuit 120 has the intrinsic offset voltage of operational amplifier.

This available digital expression formula is expressed as V2-(V1+Voff)=(V1+Voff)-VSS.Here, Voff represents the offset voltage of operational amplifier.At this moment, adopt V1=V2R6/ (R5+R6), the relation of the V2-V1 V1-VSS that the offset voltage Voff that regulating resistor 118 or 119 comes the correction calculation amplifier to produce in buffer circuit 120 causes, thereby can highly precisely reach the relation of V2-V1=V1-VSS.

By doing like this,, can satisfy the relation of V2-V1=V1-VSS and need not with operational amplifier adjusting offset voltage itself by a regulating resistor R5 or a R6.In other words, produce after the voltage V2, produce voltage V1 with it, thereby by only regulating the relation that a part can highly precisely reach V2-V1=V1-VSS.

By the way, be that the example for multiplex addressing (MLA) driving method describes above, but the present invention also can be used for general one tunnel LCD drive method line by line.In other words, under the situation that requires liquid crystal drive bias voltage relative accuracy, produce after the voltage, if voltage is divided into another voltage, then only by regulating the bias voltage that a part just can draw the relative accuracy excellence with resistance.

In addition, voltage V2 is as the positive supply 128 of the buffer circuit 120 of operational amplifier formation.By this measure, compare as the situation of the positive supply of the buffer circuit of operational amplifier formation with voltage Vout2, the reactive power that the buffer circuit 120 that operational amplifier constitutes consumes has reduced (Vout2-V2) * (liquid crystal panel consumed current), in addition, compare as the situation of positive supply 128 with voltage VH, inactivity greatly reduces (VH-V2) * (liquid crystal panel consumed current).

In this embodiment, though illustrate it is just to adopt telefault to carry out as the breaker type switching regulaor of switching regulaor 124, but the present invention is not limited thereto, even obviously the charge pump type switching regulaor that does not for example only adopt telefault to constitute by a capacitor also can be obtained same effect.

In addition, in the present invention, most of circuit can be made monolithic integrated optical circuit (IC), in the case, though the resistance ratio degree of accuracy of resistor R 5 and R6 can make up the slightly raising that draws than discreet component, but if the adjusting employing such as laser is regulated on IC then can improve the resistance ratio degree of accuracy greatly, and can improve display quality.

In sum, according to the present invention, under the situation that the public bias voltage V1 of public side and section side is produced by the buffer circuit that adopts operational amplifier, voltage V2 is by the voltage of electric resistance partial pressure generation as section side voltage, draw bias voltage V1 in the buffer circuit 120 that this voltage input operational amplifier constitutes, thereby can highly precisely draw the relation of V2-V1=V1-VSS, and then improve the quality that shows.Simultaneously, the positive supply of the buffer circuit that constitutes when operational amplifier provides from the voltage V2 as section side voltage, then can reduce the power consumption of LCD.

Claims

1. be used to drive a kind of power circuit of LCD, by the public side voltage that is added on the liquid crystal panel is carried out electric resistance partial pressure and produces the section side bias voltage by input buffer circuit, it is characterized in that another segmentation driving side voltage is to produce by the voltage of maximum voltage value in a plurality of segmentation driving side voltages is carried out electric resistance partial pressure, this voltage is input in the buffer circuit that adopts operational amplifier, and the positive supply of buffer circuit then provides from the voltage of maximum voltage value.