JP2001188618A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output stable voltage in a low power consumption state. SOLUTION: The power unit is composed of plural output circuits 22, plural current supply circuits 23, a current control circuit 24, and plural voltage dividing resistors R1-R4. Each of the resistors R1-R4 divides supplied voltage. Each output circuit 22 amplifiers divided voltage when an operation current is supplied and outputs the amplified voltage to a liquid crystal driving device as driving voltage. Each current supply circuit 23 changes the level of the operation current to be supplied to the output circuits 22. The current control circuit 24 controls the circuits 23 and eases the level change of driving voltage generated by noise. Since the noise is generated by the level switching of the driving voltage concretely, the circuit 24 changes the level of the operation current in accordance with a clock signal for instructing the level switching of the driving voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a power supply device.

[0002]

2. Description of the Related Art A power supply device used for a liquid crystal display device or the like is configured as shown in FIG. 8 when four drive voltages are generated, for example. Specifically, the power supply device includes a booster circuit 121, a plurality of output circuits 122, and a voltage dividing resistor R1.
1 to R14. Step-up circuit 121
Raises the power supply voltage VDD supplied from an external power supply (not shown) to thereby increase one of the drive voltages (the drive voltage V
4) is generated. Further, the boosted voltage Vpr is divided by the voltage dividing resistors R11 to R14. The divided boosted voltage Vpr is output to the output circuit 1
By means of 22, the driving voltages V1 to V3 are output to a driving circuit such as a liquid crystal display device.

The output circuit 122 is constituted by, for example, a voltage follower circuit having an amplification factor of 1. This voltage follower has two types, an N buffer shown in FIG. 9A and a P buffer shown in FIG. 9B. The N buffer includes a constant current circuit 131 as shown in FIG.
And an output stage provided with an N-type MOS transistor TN and a constant current circuit 132. The constant current circuit 131 controls the magnitude of the current flowing through the differential stage to be constant, and the constant current circuit 132 controls the magnitude of the current flowing through the output stage to be constant. Thus, the N buffer amplifies the supplied voltage by one and outputs it. On the other hand, as shown in FIG. 9B, the P buffer includes a differential stage provided with a constant current circuit 133 and an output stage provided with a P-type MOS transistor TP and a constant current circuit 134.
It has. The constant current circuit 133 controls the magnitude of the current flowing through the differential stage to be constant, and the constant current circuit 134 controls the magnitude of the current flowing through the output stage to be constant. As a result, the P buffer amplifies the supplied voltage by one and outputs it.

[0004]

However, the power supply device configured as described above has a problem that it is not possible to simultaneously reduce current consumption and generate a stable drive voltage.
For example, if the constant current supplied by the constant current circuits 131 to 134 is set to the lowest level at which a liquid crystal display device or the like can be driven in order to reduce the current consumed by the power supply device, a stable driving voltage is generated. become unable. Specifically, when noise occurs in the gate voltage applied to the N-type MOS transistor TN or the P-type MOS transistor TP, the level of the output drive voltage changes. But,
As described above, when the constant current is set to the lowest level, noise generated in the gate voltage cannot be reduced in a short time. Therefore, the level of the output driving voltage becomes unstable. On the other hand, if the level of the constant current supplied by the constant current circuits 131 to 134 is set large in order to mitigate the noise generated in the gate voltage in a short time, the current consumed by the power supply device increases. As described above, the power supply device having the above configuration has a problem that it is not possible to simultaneously reduce current consumption and generate a stable drive voltage. As a result, the operation reliability of the power supply device is low. Therefore, an object of the present invention is to provide a power supply device with high operation reliability. Another object of the present invention is to provide a power supply device capable of outputting a stable voltage with low power consumption.

[0005]

In order to achieve the above object, a power supply according to the present invention operates by being supplied with an operating current, and amplifies a supplied first voltage to generate a second voltage. Output means for outputting to an external device, and current control means for changing a level of the operating current at a predetermined timing to mitigate a level change of the second voltage caused by noise. .
According to the present invention, by changing the level of the operating current, the change in the level of the second voltage due to noise is reduced, so that the increase in current consumed by the power supply device is suppressed, and the second voltage with a stable level is generated. can do.

[0006] The noise is noise generated by switching the level of a drive voltage for driving the liquid crystal, and the current control means switches the level of the drive voltage at a timing at which the level of the drive voltage switches in accordance with a switching signal instructing the level switch of the drive voltage. The level of the operating current may be changed. The output means is an operational amplifier including a first constant current circuit for maintaining a constant level of an operating current, and the current control means is connected in parallel with the first constant current circuit via a switch. A second constant current circuit, and the level of the operating current supplied to the operational amplifier may be changed by turning on and off the switch. The apparatus further comprises voltage dividing means for generating a plurality of divided voltages including the first voltage by dividing the supplied supply voltage, and the output means comprises a plurality of voltage dividing means for driving a liquid crystal from the divided voltage. A voltage follower circuit for generating a drive voltage, wherein the current control unit is configured to generate the drive voltage at a timing when the noise is generated;
The level of the operating current supplied to the voltage follower circuit may be increased.

[0007]

Next, a power supply device according to an embodiment of the present invention will be described with reference to the drawings. Hereinafter, a case where the power supply device according to the embodiment of the present invention is applied to a liquid crystal display device will be described. The liquid crystal display device includes, for example, a display panel 1, a power supply device 2, a row driver 3, a column driver 4, and a control device 5, as shown in FIG. The display panel 1 includes a pair of substrates arranged to face each other, a plurality of scanning electrodes 11 formed on one substrate in the row direction, and a plurality of signal electrodes 13 formed on the other substrate in the column direction. And a liquid crystal sealed between a pair of substrates. Then, the display panel 1 displays an image using a plurality of pixels defined by intersections between the scanning electrodes 11 and the signal electrodes 13. The power supply 2
Using a power supply voltage VDD supplied from an external power supply (not shown) such as a battery, a driving voltage for driving the liquid crystal display device is generated, and supplied to the row driver 3 and the column driver 4. The detailed configuration and operation of the power supply device 2 will be described later.

[0008] The row driver 3 is connected to the scanning electrodes 11 of the display panel 1 and generates a scanning voltage from the driving voltage supplied from the power supply device 2. Then, the row driver 3 supplies the generated scanning voltage to the scanning electrode 11 at a predetermined timing. The column driver 4 is connected to the signal electrode 13 of the display panel 1.
And image data for displaying a predetermined image are sequentially provided. The column driver 4 generates a signal voltage from the drive voltage supplied by the power supply device 2 according to the provided image data, and supplies the generated signal voltage to the signal electrode 13 at a predetermined timing. The control device 5 outputs a clock signal for operation timing control to the row driver 3 and the column driver 4, and controls the operation of the row driver 3 and the column driver 4. Specifically, for example, the control device 5
The timing at which the row driver 3 supplies the scanning voltage, and
The timing at which the column driver 4 supplies the signal voltage is controlled. Thereby, control device 5 causes display panel 1 to display a predetermined image. The clock signal is also output to the power supply device 2.

Next, a detailed configuration of the power supply device 2 will be described by taking a power supply device that generates four different voltages V1, V2, V3 and V4 as an example. As shown in FIG. 2, for example, the power supply device 2 includes a booster circuit 21, three output circuits 22, three current supply circuits 23, and a current control circuit 24.
And voltage dividing resistors R1 to R4. The booster circuit 21 has an input terminal connected to a power supply input terminal (not shown) of the power supply device 2 and a power supply voltage VDD supplied from an external power supply (not shown) connected to the power supply input terminal.
To generate a boosted voltage Vpr. The output terminal of the booster circuit 21 is connected to the row driver 3 and the column driver 4,
The boosted voltage Vpr is output to the row driver 3 and the column driver 4 as a drive voltage V4 which is one of the drive voltages. The voltage dividing resistors R1 to R4 are connected in series between the ground and the output terminal of the booster circuit 21 in the order of the voltage dividing resistors R1, R2, R3 and R4. The voltage dividing resistor R1 is connected to the ground, and the voltage dividing resistor R4 is connected to the output terminal of the booster circuit 21. As a result, the boosted voltage Vpr output from the booster circuit 21 is divided by the voltage dividing resistors R1 to R4. The ground voltage VGND is supplied to the row driver 3 and the column driver 4 from the ground.

Three output circuits 22 are provided, the input terminals of which are voltage dividing resistors R1 and R2, R2 and R3, and R3.
And R4. The output circuit 22 is configured by a voltage follower circuit, operates by being supplied with the power supply voltage VDD, and amplifies the divided boosted voltage Vpr (divided voltages Vd1 to Vd3) by one. The output circuit 22 includes a constant current circuit 31 provided in a differential stage, an N-type MOS transistor TN and a constant current circuit 3 provided in an output stage, as shown in FIG.
And 2. The constant current circuit 31 has a power supply voltage VD
The constant current circuit 3 controls (holds) the magnitude of the current (operating current) flowing through the differential stage by supplying D to the constant level.
2 controls (holds) the magnitude of the current (operating current) flowing to the output stage at a constant level. As a result, the output circuit 22 amplifies the divided voltages Vd1 to Vd3 by a factor of 1, and outputs the driving voltages V1 to Vd3.
V3 is output to the row driver 3 and the column driver 4.

The current supply circuit 23 has one output circuit 22
And the magnitude of the constant current flowing through the differential stage and the output stage of the output circuit 22 is changed. This current supply circuit 2
3 is a constant current circuit 33, 34 as shown in FIG.
And switches 35 and 36. The constant current circuit 33 is connected in parallel with the constant current circuit 31 of the output circuit 22, and is connected to the output circuit 2 via a path different from that of the constant current circuit 31.
A constant current is supplied to the second differential stage. Specifically, the constant current circuit 33 is connected to a differential stage via a switch 35, and supplies a constant current to the differential stage when the switch 35 is turned on. On the other hand, the constant current circuit 34 is connected in parallel with the constant current circuit 32 of the output circuit 22, and supplies a constant current to the output stage of the output circuit 22 from a different path from the constant current circuit 32.
Specifically, the constant current circuit 34 is connected to an output stage via a switch 36, and supplies a constant current to the output stage when the switch 36 is turned on. For example, the constant current circuit 3
When the constant current circuits 1 and 32 and the constant current circuits 33 and 34 supply the same magnitude of constant current, the magnitude of the constant current supplied to each of the differential stage and the output stage is increased by turning on the switches 35 and 36. Double.

The current control circuit 24 controls the on and off of the switches 35 and 36 constituting the current supply circuit 23, thereby controlling the constant current (operation) supplied to each of the differential stage and the output stage of the output circuit 22. Current). Specifically, the current control circuit 24 generates a pulse signal of a predetermined width including an edge of the clock signal from the clock signal supplied by the control device 5, and
On and off of 5, 36 are controlled. During operation of the liquid crystal display device, noise is likely to occur when the voltage supplied to the scanning electrode 11 and the signal electrode 13 changes. For example, when the scan voltage shown in FIG. 4A is supplied to the scan electrode 11 and the signal voltage shown in FIG. 4B is supplied to the signal electrode 13, the timing T at which the levels of the scan voltage and the signal voltage change Causes noise. That is, noise occurs at a timing corresponding to the edge of the clock signal output from the control device 5. The current control circuit 24 generates a pulse signal SP shown in FIG. 4C from the clock signal supplied by the control device 5, and outputs the pulse signal SP to the switches 35 and 36. Thus, the current control circuit 24 turns on the switches 35 and 36 at the timing T. Therefore, when noise occurs, the constant current supplied to the differential stage and the output stage of the output circuit 22 increases, and the level change due to the noise can be reduced (stabilized) in a short time. In addition, the current control circuit 2
4 indicates switches 35 and 3 during a period in which no noise is generated.
Turn 6 off. As a result, current consumption in the power supply device 2 can be kept low.

Next, the power supply device 2 configured as described above
The operation of the liquid crystal display device provided with will be described. First, an external power supply is connected to a power supply input terminal of the power supply device 2. Thus, the power supply voltage VDD is supplied to the booster circuit 21 and to the output circuit 22 via the current supply circuit 23. The booster circuit 21 generates a boosted voltage Vpr by boosting the supplied power supply voltage VDD. The boosted voltage Vpr is output to the row driver 3 and the column driver 4 as the drive voltage V4, and is divided by the voltage dividing resistors R1 to R4. Output circuit 22
Is a divided voltage V divided by the voltage dividing resistors R1 to R4.
Each of d1 to Vd3 is amplified by a factor of 1, and drive voltages V1 to Vd3 are amplified.
V3 is output to the row driver 3 and the column driver 4.

At this time, the current control circuit 24
4C, a code having a predetermined width including the edge of the clock signal is generated from the clock signal supplied as shown in FIG. This allows
The current control circuit 24 turns on the switches 35 and 36 of the current supply circuit 23 at a timing T at which noise easily occurs. In this way, the output circuit 22 operates with the constant current supplied by the constant current circuits 31 and 32 except at the timing T, and at the timing T, the constant current circuits 31 and 32
It operates with a constant current supplied by the constant current circuits 33 and 34. That is, the output circuit 22 operates at a constant current larger than the constant current supplied at times other than the timing T when noise occurs. Thus, the output circuit 22 can generate stable drive voltages V1 to V3. As described above, the ground voltage VGND and the driving voltages V1 to V4 are
The power is output from the power supply device 2 to the row driver 3 and the column driver 4.

The row driver 3 generates a scanning voltage from the ground voltage VGND and the driving voltages V1 to V4 supplied from the power supply device 2, and scans the selected voltage as a scanning voltage at a predetermined timing under the control of the control device 5. Electrode 11
To supply. The column driver 4 generates a signal voltage from the ground voltage VGND and the driving voltages V1 to V4 supplied from the power supply device 2, and controls the signal electrode 13 at a predetermined timing using the selected voltage as a signal voltage under the control of the control device 5.
To supply. Specifically, the row driver 3 and the column driver 4 select a voltage necessary for driving the liquid crystal of the display panel 1 from the ground voltage VGND and the driving voltages V1 to V4 supplied from the power supply device 2. Supply. For example,
The row driver 3 selects the drive voltage V4 and supplies it to the scan electrode 11 as a scan voltage. On the other hand, the column driver 4 selects the ground voltage VGND and sets the signal electrode 13 as a signal voltage.
To supply. As a result, the maximum voltage generated by the power supply device 2 is applied to the liquid crystal of the display panel 1. The row driver 3 selects the ground voltage VGND, and the column driver 4
Selects the driving voltage V4, the display panel 1
A voltage having the opposite polarity to the above can be applied to the liquid crystal. As a result, a predetermined image is displayed on the display panel 1.

As described above, the current control circuit 24 sets the level of the constant current supplied to the output circuit 22 high at the timing T when it is expected that noise is likely to occur. Thus, even if noise occurs, the level change of the driving voltages V1 to V3 output from the output circuit 22 can be reduced in a short time. That is, stable driving voltages V1 to V4
Can be generated. In addition, the current control circuit 24
Since the level of the constant current supplied to the output circuit 22 is set high only at the timing when it is expected that noise is likely to occur, the increase in current consumption can be minimized.
As described above, since the power supply device can generate a stable drive voltage with low current consumption, it has high operation reliability.

The output circuit 22 is connected to, for example, FIG.
A voltage follower circuit configured as shown in (b) may be used. This voltage follower circuit is shown in FIG.
As shown in (b), the constant current circuit 1 provided in the differential stage
33 and a P-type MOS transistor T provided at the output stage.
P and a constant current circuit 134. Also in this case, similarly to the above, the current control circuit 24
By controlling the magnitude of the constant current supplied to the
A stable drive voltage can be generated with low current consumption.

The configuration of the current supply circuit 23 may be other than that described above. For example, a current mirror circuit having a configuration as shown in FIG. As shown in FIG. 5A, the current mirror circuit includes resistors R51 and R52 connected in series with each other, and a switch 53 for short-circuiting the resistor R52. Then, the current control circuit 24 controls the ON / OFF of the switch 53 to control the magnitude of the constant current supplied to the output circuit 22 as in the above-described embodiment. Further, the current mirror circuit connects / connects the resistors R54 and R55 and the resistor R55, which are connected in parallel with each other, as shown in FIG.
A switch 56 for disconnection. In this case, the current control circuit 24 controls the ON / OFF of the switch 56 to control the magnitude of the constant current supplied to the output circuit 22 as in the above embodiment.

The number of resistors and switches included in the current mirror circuit can be changed as needed.
For example, the magnitude of the constant current supplied to the output circuit 22 can be controlled in a stepwise manner by using three or more resistors and switching the steps in a stepwise manner. When the output circuit 22 includes the P-type MOS transistor TP as shown in FIG. 9B, the current mirror circuit is configured as shown in FIG. 6A or 6B, for example. You. Further, the output circuit 22 may be used as a differential amplifier. Also in this case, similarly to the above, by controlling the magnitude of the constant current supplied to the differential amplifier, a stable voltage with low current consumption can be generated.

Further, as shown in FIG. 7, for example, the power supply device 2 is composed of an output circuit 22 having an N-type MOS transistor TN and an output circuit 61 having a P-type MOS transistor TP. May be. Again,
The current control circuit 24 outputs the output circuits 22, 6 in the same manner as described above.
By controlling the magnitude of the constant current supplied to 1, a stable voltage with low current consumption can be generated. Further, the power supply device of the present invention can be applied to any display device other than the liquid crystal display device as long as noise is generated at a timing corresponding to the edge of the clock signal in the same manner as described above. For example, PDP (plasma display), E
The present invention is applicable to display devices such as an L (electroluminescence) panel and an FED (field emission display).

[0021]

As is clear from the above description, according to the present invention, the level of the current can be changed in accordance with the timing at which noise occurs, and the level of the output voltage can be stabilized. That is, a stable voltage can be generated with low power consumption. Thus, the power supply device has high operation reliability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a power supply device used in the liquid crystal display device shown in FIG.

FIG. 3 is a configuration diagram of an output circuit and a current supply circuit that configure the power supply device of FIG. 2;

4A is a waveform diagram of a scanning voltage supplied to a scanning electrode forming a liquid crystal display device, and FIG. 4B is a waveform diagram of a signal voltage supplied to a signal electrode forming a liquid crystal display device; FIG. 3C is a waveform diagram of a control signal output to a current supply circuit by a current control circuit included in the power supply device.

FIG. 5 is another configuration diagram of a current supply circuit included in the power supply device of FIG. 2;

FIG. 6 is another configuration diagram of a current supply circuit included in the power supply device of FIG. 2;

FIG. 7 is another configuration diagram of the power supply device.

FIG. 8 is a configuration diagram of a conventional power supply device.

FIG. 9 is a configuration diagram of an output circuit configuring the power supply device shown in FIG. 8;

[Explanation of symbols]

1 display panel, 2 power supply device, 3 row driver,
4 column driver, 5 control device, 11 scanning electrode,
13 ... signal electrode, 21 ... booster circuit, 22 ... output circuit, 23 ... current supply circuit, 24 ... current control circuit, 3
1, 32, 33, 34: constant current circuit, 35, 36: switch, R1 to R4: voltage dividing resistor, TN: N-type MOS transistor, TP: P-type MOS transistor

Claims (4)

[Claims] An operation is performed by supplying an operating current, and the supplied first voltage is amplified to generate a second voltage.
A power supply comprising: an output unit that outputs to an external device; and a current control unit that changes a level of the second voltage caused by noise by changing a level of the operation current at a predetermined timing. apparatus. 2. The method according to claim 1, wherein the noise is generated by switching a level of a driving voltage for driving the liquid crystal, and the current control means switches the level of the driving voltage in accordance with a switching signal instructing a level switching of the driving voltage. The power supply device according to claim 1, wherein the level of the operation current is changed at a timing. 3. The operational amplifier having a first constant current circuit for maintaining a level of an operating current constant, wherein the current control means includes a first constant current circuit via a switch. And a second constant current circuit connected in parallel with the first and second switches, and turning on and off the switch to change a level of an operating current supplied to the operational amplifier. The power supply as described. 4. A voltage dividing means for dividing a supplied voltage to generate a plurality of divided voltages including the first voltage, wherein the output means drives a liquid crystal from the divided voltage. A voltage follower circuit that generates a plurality of drive voltages for performing the operation, wherein the current control unit increases a level of an operation current supplied to the voltage follower circuit at a timing when the noise occurs. The power supply device according to claim 1.