JP2000284754A - Power supply - Google Patents

Abstract

(57) [Summary] To stably drive a display element. SOLUTION: The supplied divided voltages Vd1 to Vd3 are
Amplification is performed by a corresponding pair of an N-type operational amplifier 231 having an N-type drive transistor in the output stage and a P-type operational amplifier 232 having a P-type drive transistor in the output stage. A very small resistor r is connected between the input terminals of the pair of operational amplifiers 231 and 232 to make the input voltage of the P-type operational amplifier 232 lower than the input voltage of the N-type operational amplifier 231. One end of a current path of the switch SW is connected to the output terminal of the P-type operational amplifier 232, and the other end of the switch SW is connected to the output terminal of the corresponding N-type operational amplifier 231. The through current prevention circuit 24 turns off the switch SW when the divided voltage Vd1 is equal to or lower than the reference voltage Vref, thereby preventing a large through current from flowing through the simultaneously turned on P and N drive transistors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly to a power supply device suitable for driving a display element and capable of being started stably.

[0002]

2. Description of the Related Art When a power supply circuit of a liquid crystal display device generates, for example, four drive voltages, the power supply voltage is boosted by a booster circuit as shown in FIG.
The voltage is divided by 1 to R4, and the divided voltage is output as drive voltages V1 to V4 via a voltage follower circuit. The operational amplifier that constitutes the voltage follower circuit has
As shown in FIG. 6A, a P-type operational amplifier in which an output stage transistor (driver transistor) is constituted by a P-type MOS transistor TP, and as shown in FIG.
Output stage transistor (driver transistor) is N-type M
There is an N-type operational amplifier composed of OS transistors.

The output voltage of a voltage follower circuit composed of a P-type operational amplifier and an N-type operational amplifier is biased to a power supply voltage and a ground voltage, respectively, due to a change in load.
Therefore, in the voltage follower circuit shown in FIG. 5, it is difficult to obtain a stable and accurate drive voltage.

[0004] Therefore, a power supply circuit has been proposed in which a P-type operational amplifier and an N-type operational amplifier are paired and the output voltages of the P-type operational amplifier and the N-type operational amplifier are averaged to obtain an accurate and stable output voltage. Have been.

In this case, as shown in FIG. 7, a small resistor r is inserted between the input terminals of a pair of P-type operational amplifiers and the input terminals of an N-type operational amplifier. Due to this minute resistance r, the input potential of the P-type operational amplifier is slightly lower than the input potential of the N-type operational amplifier, and the P-type driver transistor TP of the P-type operational amplifier is set.
And the N-type driver transistor TN of the N-type operational amplifier are not turned on at the same time.

According to this configuration, normally, only one of the P-type driver transistor TP and the N-type driver transistor TN is turned on, and the current flowing to the output stage is a constant current (usually several μA or less). No. When the output voltage rises above the cap voltage generated by the small resistor r, the N-type driver transistor TN turns on and lowers the output voltage. Conversely, when the output voltage falls below the cap voltage, , The P-type driver transistor TP is turned on to increase the output voltage. In this way, the output voltage is maintained at a steady value. The gap voltage between both ends of the micro resistor r depends on the display quality of the liquid crystal and the driver transistor TN.
And TP are set to several tens mv in consideration of the fact that TP and TP are not simultaneously turned on.

[0007]

However, when the output voltage of the booster circuit is not sufficiently high, for example, when the power is turned on, the potential difference (gap voltage) between both ends of the minute resistor r becomes very small, and P The operational amplifier P-type driver transistor TP and the N-type operational amplifier N-type driver transistor TN are simultaneously turned on. In such a case, a large through current flows from the power supply to the ground via the turned-on P-type driver transistor TP and the N-type driver transistor TN, so that the power supply device cannot be started normally and the display device cannot be driven. .

The present invention has been made in view of the above circumstances, and has as its object to provide a power supply device that can be started normally. Another object of the present invention is to provide a power supply device capable of supplying stable power for display to a display device. Further, the present invention provides a power supply device which includes an amplifier element including an amplifier having a P-channel field-effect transistor in an output stage and an amplifier having an N-channel field-effect transistor in an output stage and operates stably. For other purposes.

[0009]

To achieve the above object, a power supply device according to a first aspect of the present invention comprises a voltage generating means for generating a plurality of voltages from a supply voltage, and an output stage comprising an N-channel field effect. A first amplifying element comprising a transistor and amplifying the voltage generated by the voltage generating means; and a second amplifying element comprising an output stage comprising a P-channel field effect transistor and amplifying the voltage generated by the voltage generating means. Amplifying element connected substantially in parallel between the voltage generating means and the output terminal of the power supply device, and comparing a supply voltage to the voltage generating means with a predetermined voltage. And interrupting means for interrupting a current flowing between the output terminal of the first amplifier element and the output terminal of the second amplifier element when the voltage is equal to or lower than a predetermined voltage.

According to this configuration, when the supply voltage to the voltage generating means is equal to or less than a predetermined value, for example, immediately after the power supply is turned on, the output terminal of the first amplifying means and the second amplifying means are connected. The current flowing between the output terminal of the means is cut off. For this reason, even if the N-channel field-effect transistor of the first amplifying element and the P-channel field-effect transistor of the second amplifying element are turned on at substantially the same time because the supply voltage to the voltage generating means is small, it is turned on. A large through current can be prevented from flowing through both transistors. Therefore, the power supply device can be started normally, and the display element can be driven stably.

The cutoff means may include, for example, a switch inserted between the first amplifying element and an output terminal or between the second amplifying element and an output terminal of the power supply, Switch control means for comparing the supply voltage to the voltage generation means with a predetermined voltage, turning off the switch when the voltage is lower than the predetermined voltage, and turning on the switch when the voltage is higher than the predetermined voltage.

The switch control means compares the voltage generated by dividing the supply voltage to the voltage generation means with a reference voltage to determine whether the supply voltage to the voltage generation means is less than a predetermined voltage. It may be determined whether or not.

The voltage generating means comprises, for example, a voltage dividing circuit for dividing a supply voltage to generate a plurality of voltages. In this case, the switch control means compares one of the divided voltages generated by the voltage dividing circuit with a reference voltage to determine whether or not the supply voltage to the voltage generation means is less than a predetermined voltage. It may be determined.

A power supply according to a second aspect of the present invention comprises:
Voltage generating means for dividing the supply voltage to generate a plurality of voltages, an output stage comprising an N-channel field effect transistor, a first amplifying element for amplifying the voltage generated by the voltage generating means, and an output stage Is composed of a P-channel field effect transistor, and a second amplifying element for amplifying the voltage generated by the voltage generating means is provided substantially in parallel between the voltage generating means and an output terminal of the power supply device. Amplifying means connected and configured, a switch interposed between the first amplifying element and an output terminal or between the second amplifying element and an output terminal of the power supply device; Comparing a specific voltage of the plurality of voltages generated by the voltage generating means with the reference voltage, and when the specific voltage is less than the reference voltage,
Switch control means for turning off the switch and turning on the switch when the voltage is equal to or higher than a reference voltage.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a power supply device according to the present invention applied to a liquid crystal display device. As shown in FIG. 1, the liquid crystal display device according to this embodiment includes a display panel 1, a power supply device 2, a row driver 3, a column driver 4, and a control device 5. The display panel 1 includes a first substrate and a second substrate which are arranged to face each other, a plurality of scanning electrodes 11 which are arranged in a row direction on the first substrate, and a plurality of scanning electrodes 11 which are arranged in a column direction on the second substrate. A plurality of signal electrodes 13 and liquid crystal sealed between the two substrates, and an image is displayed by a plurality of pixels defined by intersections of the scanning electrodes 11 and the signal electrodes 13.

As shown in FIG. 2, the power supply device 2 includes a driving voltage generation comparing circuit 21, a boosting circuit 22, and a voltage dividing circuit 2.
3 and a driving current V4 for driving the liquid crystal display panel 1,
V1 (V4>V3>V2> V1) and the ground voltage VGD (V
1> VGD) and supplies it to the row driver 3 and the column driver 4.

The drive voltage generation comparison circuit 21 compares a reference voltage Vref supplied from the outside with a divided voltage Vd1, which will be described later, and generates a predetermined voltage according to the comparison result.
Feed to 2.

The boosting circuit 22 boosts the voltage supplied from the driving voltage generation comparing circuit 21 and supplies the boosted voltage Vpr to the voltage dividing circuit 23.

The voltage dividing circuit 23 includes voltage dividing resistors R1 to R4 for dividing the boosted voltage Vpr supplied from the voltage boosting circuit 22, and divided voltages Vd1 to Rd1 divided by the voltage dividing resistors R1 to R4.
The first to third voltage follower circuits 23-1, which amplify Vd3 about 1 times and output as drive voltages V1 to V3,
23-2 and 23-3. The first to third voltage follower circuits 23-1, 23-2, and 23-3 are:
Each of the N-type operational amplifier 231 and the P-type operational amplifier 2
32 and a small resistor r.

As shown in FIG. 2, the voltage dividing resistors R1 to R4
Are connected in series between the output terminal of the booster circuit 22 and the ground potential in the order of the voltage dividing resistors R4, R3, R2 and R1. Further, the first to third voltage follower circuits 2
The minute resistors r of 3-1, 23-2, and 23-3 are respectively connected to the voltage dividing resistors R1 and R2, the voltage dividing resistors R2 and R3, and the voltage dividing resistors R3 and R4. ~ R4
It is located between. That is, the voltage dividing resistors R1 to R4 and the minute resistors r are connected in series substantially alternately.

First to third voltage follower circuits 23
In each of -1, 23-2 and 23-3, an N-type operational amplifier 23 is connected to one end of the minute resistor r (on the side of the booster circuit 22).
The input terminal of the P-type operational amplifier 232 is connected to the other input terminal (ground potential side) of the small resistor r.

The N-type operational amplifier 231 is composed of a circuit similar to the N-type operational amplifier shown in FIG. 6B, and has an N-type MOS transistor TN (N-channel field effect transistor) at an output stage. The N-type operational amplifier 231 has divided voltages Vd1 to Vd1 divided by the dividing resistors R1 to R4.
Of d4, the corresponding divided voltages Vd1 to Vd3 are amplified by about 1 times and output. Also, the N-type operational amplifier 231 has one
P-type operational amplifier 232 arranged corresponding to pair
Is composed of a circuit similar to the P-type operational amplifier shown in FIG. 6A, and includes a P-type MOS transistor TP (P-channel field effect transistor) at an output stage. The P-type operational amplifier 232 amplifies the voltage input to the corresponding N-type operational amplifier 231 by a factor of about 1 which is smaller than the voltage input by the minute resistor r and outputs the amplified voltage.

The small resistance r is set by making the potential of the input terminal of the pair of P-type operational amplifiers 232 slightly lower than the potential of the input terminal of the N-type operational amplifier 231 so that the P-type MOS transistors TP of the pair of P-type operational amplifiers 232 are formed. And the N-type MOS transistors TN of the N-type operational amplifier 231 are not turned on at the same time.
One input terminal.

The through current prevention circuit 24 includes a comparison circuit 241
, An inverting circuit 242, and switches SW1 to SW3, and an N-type MOS at an output stage of the N-type operational amplifier 231.
Transistor TN and P of output stage of P-type operational amplifier 232
This is a circuit for preventing a large amount of through current from flowing from the power supply to the ground via the turned-on transistor when the type MOS transistor TP is turned on at the same time.

The comparator 241 determines whether or not the boosted voltage Vpr output from the booster 22 is equal to or higher than a predetermined value, and supplies a signal corresponding to the determination result to the inverting circuit 242. More specifically, the comparison circuit 241 is set so as to have a predetermined voltage (divided voltage Vd1) among the voltages obtained by dividing the boosted voltage Vpr, and substantially the same magnitude as the divided voltage Vd1. The divided voltage Vd1 is compared with the reference voltage Vcr. When the divided voltage Vd1 is equal to or higher than the comparison reference voltage Vcr, a high-level signal is output.
When the voltage is less than cr, the low level signal is output to the inverting circuit 2
42.

The inverting circuit 242 inverts the level of the signal supplied from the comparing circuit 241 and switches SW1 to SW
3 gate. That is, when the signal supplied from the comparison circuit 241 is at a low level, the inversion circuit 242 supplies a high-level signal to the gates of the switches SW1 to SW3 to turn on the switches SW1 to SW3. When the supplied signal is high level,
A low-level signal is supplied to the gates of the switches SW1 to SW3, and the switches SW1 to SW3 are turned off.

Each of the switches SW1 to SW3 is formed of, for example, an n-channel field-effect transistor. One end (drain) of a current path is connected to the output terminal of the corresponding P-type operational amplifier 232, and the other end (source) is connected to the corresponding output. Terminal T1
To T3, the gate of which is connected to the output terminal of the inverting circuit 242. The switches SW1 to SW3 are turned on by a high-level signal supplied from the inversion circuit 242, and turned off by a low-level signal.

In the power supply device configured as described above, until the boosted voltage Vpr output from the booster circuit 22 reaches a desired level, the P-type of the output stage of the pair of P-type operational amplifiers 232. Even if the N-type MOS transistor TP and the N-type MOS transistor TN at the output stage of the N-type operational amplifier are turned on at the same time, by turning off the switch SW, P
The current path between the P-type MOS transistor TP at the output stage of the type operational amplifier 232 and the N-type MOS transistor TN at the output stage of the N-type operational amplifier 231 is disconnected. Thus, it is possible to prevent a large amount of through current from flowing through the turned-on P-type MOS transistor TP and the turned-on N-type MOS transistor TN. Therefore, the operation of the power supply device when the boosted voltage Vpr is not large, such as when the power is turned on, can be stabilized.

The row driver 3 shown in FIG. 1 is connected to the scanning electrodes 11 of the display panel 1, generates a scanning voltage from a plurality of driving voltages (VGD, V 1 to V 4) supplied from the power supply 2, and The scanning voltage is sequentially applied to the selected scanning electrodes 11 in accordance with the timing control signal from.

The column driver 4 is connected to the signal electrode 13 of the display panel 1, generates a signal voltage from a plurality of drive voltages (VGD, V 1 to V 4) supplied from the power supply device 2, and generates a signal voltage from the control device 5. The signal electrode 13 according to the control signal
Is applied with a signal voltage.

The control device 5 controls the entire operation of the row driver 3 and the column driver 4. For example, a timing signal for outputting a scanning voltage and a signal voltage to the row driver 3 and the column driver 4 is supplied.

Next, the operation of the liquid crystal display device configured as described above will be described. First, when power is turned on to the power supply device 2, the reference voltage Vref is input to the power supply device 2. The reference voltage Vref input to the power supply device 2 is input to the booster circuit 22 via the drive voltage generation / comparison circuit 21 and supplied to the voltage divider circuit 23 as the boosted voltage Vpr and output to the outside as the drive voltage V4. You.

Immediately after the power is turned on, the boosted voltage Vpr, which is the output of the booster circuit 22, gradually increases.
4) is smaller than the desired voltage value, the divided voltage Vd1
Is smaller than the comparison reference voltage Vcr. In this case, the comparison circuit 241 inputs a low-level signal to the inversion circuit 242, and outputs a high-level signal from the inversion circuit 242 to the switch S.
It is supplied to the gates of W1 to SW3. With this high-level signal, the switches SW1 to SW3 are turned off, and the output terminal of the P-type operational amplifier 232 is cut off from the output terminal of the N-type operational amplifier 231 in the pair of N-type and P-type operational amplifiers 231 and 232. Therefore, the gap voltage (small resistance r
Is small, the P-type MOS transistor TP and the N-type MOS transistor TN are both turned on.
A situation in which a large through current flows through the P-type MOS transistor TP and the N-type MOS transistor TN can be prevented.

The boosted voltage Vpr (= V4) gradually rises with the lapse of time from the power-on, and when the boosted voltage Vpr becomes higher than a desired value, the divided voltage Vd1 becomes larger than the reference voltage Vcr for comparison, and the comparison circuit 241 goes high. Is output to the inverting circuit 242. The inversion circuit 242 supplies a low-level signal to the gates of the switches SW1 to SW3, and the switches SW1 to SW3 are turned on. As a result, the N-type MOS transistor TN and the P-type MOS transistor TP of the pair of N-type and P-type operational amplifiers 231 and 232 are both connected to the output terminals, and are turned on / off while maintaining a predetermined balance.
Here, when the voltages V1 to V3 at the output terminals rise beyond the gap voltage, the N-type MOS transistor TN at the output stage of the N-type operational amplifier 231 is turned on, and the voltage is reduced.
On the other hand, when the voltages V1 to V3 at the output terminals fall below the gap voltage, the P-type M of the output stage of the P-type
The OS transistor TP is turned on, and the voltage is raised. In this way, the voltages V1 to V3 are maintained at almost desired values.

The row driver 3 controls the ground voltage VGD and the driving voltage VGD according to the timing signal supplied from the control device 5.
An appropriate scanning voltage is selected from 1 to V4, a selection signal of a predetermined waveform is applied to the scanning electrode 11 in the selected state, and a non-selection signal of a predetermined waveform is applied to the scanning electrode 11 in the non-selected state. Apply each.

The column driver 4 selects an appropriate signal voltage from the ground voltage VGD and the driving voltages V1 to V4 in accordance with the supplied image signal, and applies the selected signal voltage in accordance with the timing signal from the control device 5 to each signal. Applied to the electrode 13.

In this way, an image according to the image signal is displayed on the pixel defined by the intersection of the scanning electrode 11 and the signal electrode 13 in the selected state of the display panel 1.

As described above, the power supply device according to the embodiment of the present invention has the boosted voltage Vpr (=
When V4) is lower than the desired value, the N-type operational amplifier 23
1 and the output terminal of the P-type operational amplifier 232 are electrically disconnected. Therefore, the N-type MOS transistor TN and the P-type MOS transistor TP at the output stage of the pair of operational amplifiers 231 and 232 that are substantially connected in parallel are both turned on, thereby preventing a large through current from flowing. The power supply can be started normally.

Note that the present invention is not limited to the above embodiment, and various modifications and applications are possible. For example, in this embodiment, four voltage follower circuits forming a pair of an N-type operational amplifier and a P-type operational amplifier are used.
Two drive voltages (V1 to V4) were obtained. However, the number of voltage follower circuits can be arbitrarily changed according to the number of necessary drive voltages.

In the above description, the power supply unit compares the comparison reference voltage Vcr with the divided voltage Vd1 to obtain
It was determined whether the boosted voltage Vpr reached the predetermined voltage. However, the configuration for determining whether or not the boosted voltage Vpr has reached the predetermined voltage is not limited to the above-described embodiment, and may be any configuration.

For example, when the reference voltage Vref is substantially equal to the divided voltage Vd1 in the normal state (during normal operation), the boosted voltage Vpr is calculated by comparing the reference voltage Vref with the divided voltage Vd1. It may be determined whether a predetermined voltage has been reached. In this case, the divided voltage Vd1 is equal to the reference voltage Vref.
When smaller, the switches SW1 to SW3 are turned off.

The switches SW1 to SW3 may be turned off when the gap voltage (the voltage between both ends of the minute resistor r) and the reference voltage are compared and the gap voltage is equal to or lower than the reference voltage.

In the above description, the boosted voltage Vpr (= V
4) When the steady voltage is reached, the switches SW1 to SW3
Is turned on, but if generation of a large through current can be prevented, the timing of turning on the switches SW1 to SW3 is as follows.
Optional. For example, even when the boosted voltage Vpr is smaller than the steady voltage, if the gap voltage is large enough to prevent a through current, the switches SW1 to SW3 may be turned on.

FIG. 3 shows an example of the configuration of a power supply device in the case where the gap voltage is large enough to prevent a through current even if the boosted voltage Vpr is 90% of the steady voltage. As shown in FIG. 3, the power supply device includes resistors r1 and r2 (resistance ratio 1: 9) that divides the reference voltage Vref by 9/10.

In this case, the switches SW1 to SW3 are turned off until the divided voltage Vd1 becomes 9/10 times the reference voltage Vref, and the turned-on P-type MOS transistor TP and N-type MOS transistor are turned on. A large through current is prevented from flowing through the TN. When the magnitude of the divided voltage Vd1 becomes 9/10 times the magnitude of the reference voltage Vref, the switches SW1 to SW3 are turned on. Even in this case, the P-type MOS transistor TP and the N-type MOS
Since a large amount of through current does not flow through the transistor TN, the power supply system can operate stably.

In the case of the power supply device shown in FIG.
2, a through current always flows and power is consumed. FIG. 4 shows a power supply device which operates with low power consumption and can obtain the same effect as the power supply device shown in FIG.

The power supply device shown in FIG. 4 includes a comparison resistor r between the small resistor r of the first voltage follower circuit 23-1 and the small resistor r of the second voltage follower circuit 23-2.
3 are arranged. The comparison circuit 241 has a reference voltage V
ref and a feedback voltage Vback higher than the voltage Vd1 input to the comparison circuit 241 of the power supply device of FIG. And the feedback voltage v
When the back is lower than (less than) the reference voltage Vref, the switches SW1 to SW3 are turned off, and when the feedback voltage Vback is higher than the reference voltage Vref, the switches SW1 to SW3 are turned on.

Even in such a configuration, the N-type operational amplifier 2 may be used before the boosted voltage Vpr becomes sufficiently large, for example, when the power is turned on.
The output terminal of the P-type operational amplifier 232 and the output terminal of the P-type operational amplifier 232 can be electrically cut off to prevent a large through current from flowing, and the power supply device can be started stably. The reference voltage Vref and the feedback voltage Vb larger than the divided voltage Vd1
In order to turn on / off the switches SW1 to SW3 in comparison with the power supply device shown in FIG.
When a certain size is reached, the N-type operational amplifier 23
1 and the P-type operational amplifier 232 are operated, so that the power supply device 2 can be operated stably. Furthermore, since it is not necessary to use the resistors r1 and r2 required to obtain one voltage input to the comparison circuit 241 of the power supply device 2 shown in FIG. Power consumption can be reduced.

The physical structure of the voltage dividing resistors R1 to R4 and the minute resistor r is arbitrary as long as a desired voltage can be generated. For example, each resistor need not be formed of a single element, but may be formed of a series circuit or a parallel circuit of a plurality of resistance elements, or a combination thereof. Further, although the voltage dividing circuit 23 including a resistance element is shown, a voltage dividing circuit including a plurality of capacitors connected in series can be used.

In the above description, the switches SW1 to SW3 have been constituted by N-type field effect transistors. However, the configuration of the switches SW1 to SW3 may be any configuration, and may be, for example, a P-channel field-effect transistor or a relay switch.

From the P-type field-effect transistor to the switch S
When configuring W1 to SW3, one end of the current path of the P-type field effect transistor is connected to the corresponding P-type operational amplifier 232.
And the other end is connected to the corresponding output terminal T1 to T3.
Connect to Then, the gate is directly connected to the output terminal of the comparison circuit 241 without passing through the inversion circuit 242. P
The switches SW1 to SW3 configured by the channel field effect transistors are turned on by a low level signal supplied from the comparison circuit 241, and are turned off by a high level signal.

With such a configuration, the P-type MOS of the output stage of the pair of operational amplifiers substantially connected in parallel is also provided.
Since both the transistor TP and the N-type MOS transistor TN are turned on, a large through current can be prevented from flowing, and the power supply device can be started normally. Further, since an inversion circuit is not required, the inversion circuit can be omitted, and the configuration of the power supply device can be simplified.

In the above description, the switches SW1 to S
W3 is provided at the output terminal of the P-type operational amplifier. However, the switches SW1 to SW3 are provided at the output terminal of the N-type operational amplifier,
When the gap voltage is less than the predetermined value, the switches SW1 to SW3 may be turned off to cut off the current path between the N-type operational amplifier and the output terminal of the power supply circuit.

FIGS. 6A and 6B respectively show P
FIG. 4 is a diagram illustrating an example of the configuration of a type operational amplifier and an N-type operational amplifier. The operational amplifier includes a P-type MOS transistor in one output stage of the pair of operational amplifiers and an N-type MOS transistor in the other output stage. If so, the configuration of the operational amplifier can be any configuration.

The power supply device of the present invention is not limited to a power supply device for a liquid crystal display element, but includes a PDP (plasma display), an EL (electroluminescence) panel, and an FE.
A display device such as a D (field emission display) or the like requires a plurality of voltages for displaying a plurality of gradations and / or a plurality of colors, and is widely applicable as a power supply for a display element. Further, the present invention is naturally applicable to a power supply device for supplying power to a device other than the display device.

[0056]

As described above, according to the power supply device of the present invention, such as immediately after the power supply is turned on,
When the supply voltage to the voltage generation means is equal to or less than a predetermined value, the first
The current flowing between the output terminal of the amplifying means and the output terminal of the second amplifying means is cut off. For this reason, even if the N-channel field-effect transistor of the first amplifying element and the P-channel field-effect transistor of the second amplifying element are turned on at substantially the same time because the supply voltage to the voltage generating means is small, it is turned on. A large through current can be prevented from flowing through both transistors. Therefore, the power supply device can be started normally, and the display element can be driven stably.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a configuration of the power supply device of FIG.

FIG. 3 is a block diagram illustrating a modification of the power supply device of FIG. 2;

FIG. 4 is a block diagram showing a modification of the power supply device of FIG.

FIG. 5 is a diagram showing a configuration of a conventional power supply device.

FIG. 6A is a circuit diagram of a P-type operational amplifier,
(B) is a circuit diagram of the N-type operational amplifier.

FIG. 7 is a diagram showing a configuration of a conventional power supply device.

[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 ... comparison circuit for generating drive voltage, 2
2, booster circuit, 23, voltage divider circuit, 24, through current prevention circuit, 231, N-type operational amplifier, 232, P-type operational amplifier, 241, comparison circuit, 242,.・ Inverting circuit, TN
..N-type driver transistors, TP ... P-type driver transistors

Claims (5)

[Claims] 1. A voltage generating means for generating a plurality of voltages from a supply voltage, a first amplifying element wherein an output stage is constituted by an N-channel field effect transistor and amplifies a voltage generated by the voltage generating means; The output stage comprises a P-channel field effect transistor, and a second amplifying element for amplifying the voltage generated by the voltage generating means is provided between the voltage generating means and an output terminal of the power supply device. Amplifying means configured to be connected in parallel, comparing a supply voltage to the voltage generating means with a predetermined voltage,
The output terminal of the first amplifying element and the second
And a cutoff unit for cutting off a current flowing between the output end of the amplification element and the power supply device. 2. A switch interposed between the first amplifying element and an output terminal or between the second amplifying element and an output terminal of the power supply device; Comparing the supply voltage to the voltage generation means with a predetermined voltage,
Switch control means for turning off the switch when the voltage is lower than a predetermined voltage and turning on the switch when the voltage is higher than a predetermined voltage;
The power supply device according to claim 1, comprising: 3. The switch control means compares a voltage generated by dividing the supply voltage to the voltage generation means with a reference voltage, so that the supply voltage to the voltage generation means is less than a predetermined voltage. The power supply device according to claim 2, wherein it is determined whether or not the power supply is present. 4. The voltage generating means comprises a voltage dividing circuit which divides a supply voltage to generate a plurality of voltages, and wherein the switch control means comprises one of a divided voltage generated by the voltage dividing circuit; By comparing with the reference voltage,
The power supply device according to claim 2, wherein it is determined whether a supply voltage to the voltage generation unit is lower than a predetermined voltage. 5. A voltage generating means for dividing a supply voltage to generate a plurality of voltages, and an output stage comprising an N-channel field effect transistor, wherein a first amplifier amplifies the voltage generated by said voltage generating means. An element and an output stage comprising a P-channel field-effect transistor, and a second amplifying element for amplifying a voltage generated by the voltage generating means, between the voltage generating means and an output terminal of the power supply device. Amplifying means configured to be connected substantially in parallel, between the first amplifying element and the output terminal, or between the second amplifying element and the output terminal of the power supply device And a specific voltage of the plurality of voltages generated by the voltage generating means is compared with a reference voltage.When the specific voltage is lower than the reference voltage, the switch is turned off, and when the specific voltage is higher than the reference voltage, Switch to A main routine switch control means, and a power supply device, characterized in that.