JP2006133406A - Liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the size and cost of a liquid crystal display apparatus mounted in an electronic appliance. <P>SOLUTION: The liquid crystal display apparatus is equipped with: a liquid crystal display panel 2; a source driver 3 connected to a data line of the liquid crystal display panel 2; a gate driver 4 connected to a scanning line of the liquid crystal display panel 2; and a LCD substrate 5 connected to the gate driver 4 and the source driver 3 and including a timing controller IC 6 and a power supply circuit 9 to generate a positive or negative output voltage from an input voltage by using a PWS signal sent from the timing controller IC 6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device mounted on an electronic device such as a printer.

For example, as shown in FIG. 1, a liquid crystal display device mounted on an electronic device such as a printer is a DC-
The DC converter 7 is mounted on the LCD substrate 5 and ± 15 V to be supplied to the gate driver is generated by the DC-DC converter IC 7. However, since the DC-DC converter IC 7 is expensive, it hinders cost reduction of the liquid crystal display device. DC-
The mounting area of the DC converter IC 7 itself and its peripheral circuits makes it difficult to reduce the size of the LCD substrate and hence the liquid crystal display device.

A configuration for generating a DC voltage to be supplied to a liquid crystal display panel without using a DC-DC converter IC is described in Patent Documents 1 to 3, for example.

In Patent Document 1, a voltage value VA (positive voltage) necessary for driving a display panel is output to a potential line, and a voltage value VB (negative voltage) is generated by connecting to the potential line of the voltage boosting circuit. A liquid crystal display device including a negative voltage generating circuit is described. In this liquid crystal display device, a switching control circuit is provided in the source driver, the switching control circuit and the FET of the booster circuit are electrically connected, and switching of the FET of the booster circuit is controlled by the switching control circuit. The switching control circuit includes a voltage dividing circuit, a voltage comparison circuit, an oscillator, an oscillation control circuit, and a buffer.

Patent Document 2 discloses a booster circuit that boosts VDD with reference to the low potential side voltage Vss to generate Vout, a voltage adjustment circuit that generates VLCD from Vout with reference to Vss, and V
A liquid crystal display device including a boost clock adjusting circuit that compares out and VLCD and controls a switching element of the boost circuit based on the comparison result is described.

Patent Document 3 discloses a first booster circuit that boosts VDD to Vout with reference to Vss;
A regulator circuit that generates a center potential VC from Vout by referring to Vref using Vss as a reference, and a first circuit that generates potential levels V2, V1, MV1, and MV2 from a potential difference between the potential level V3 and the center potential VC using Vss as a reference. A liquid crystal display device comprising two booster circuits is described.
JP 2001-75539 A JP 2001-21635 A JP 2002-189454 A

In the liquid crystal display device described in Patent Document 1, it is necessary to provide an oscillation circuit or the like in the source driver, which may complicate the configuration of the source driver and increase the size. Therefore, with such a configuration, it is impossible to reduce the size and cost of a liquid crystal display device mounted with an electronic device. In particular, when a liquid crystal display device is mounted on an electronic device such as a printer, the electronic device such as a printer may be prevented from being downsized unless the size of the liquid crystal display device including the driver substrate is reduced.

Further, in the liquid crystal display device described in Patent Document 2, the switching element of the voltage adjustment circuit is driven using a clock signal, but a boost clock adjustment circuit is necessary, and the configuration becomes complicated. Therefore, with such a configuration, it is impossible to reduce the size and cost of a liquid crystal display device mounted with an electronic device.
In the liquid crystal display device described in Patent Document 3, the first booster circuit and the oscillation circuit that drives the switching elements constituting the third booster circuit are not clearly described, but it is considered that it is necessary to separately provide an oscillation circuit. In addition, the provision of a separate oscillation circuit may hinder downsizing and cost reduction of the liquid crystal display device.

An object of the present invention is to reduce the size and cost of a liquid crystal display device mounted on an electronic device.

A liquid crystal display device according to a first aspect of the present invention is a liquid crystal display device mounted on a printer, and includes a liquid crystal display panel, a source driver connected to a data line of the liquid crystal display panel, and a scanning line of the liquid crystal display panel. A connected gate driver; a timing controller IC connected to the gate driver and the source driver; and a power supply circuit that generates a positive / negative output voltage from an input voltage using a PWS signal output from the timing controller IC; An LCD substrate.

The power supply circuit includes a first switching element driven by the PWS signal, and the first switching element.
A switching circuit including a second switching element that is driven by the output of the switching element and switches the input voltage; a first rectifying / smoothing circuit that rectifies and smoothes the output from the switching circuit and outputs a positive voltage; A first output circuit including a first shunt regulator that generates the positive output voltage from a positive voltage output from one rectifying and smoothing circuit; and a first output circuit that rectifies and smoothes the output from the switching circuit and outputs a negative voltage. A two-rectifying smoothing circuit;
And a second output circuit including a second shunt regulator that generates the negative output voltage from the negative voltage output from the second rectifying and smoothing circuit.

In this liquid crystal display device, on the LCD substrate, a positive and negative output voltage is generated from the input voltage by the power supply circuit using the PWS signal output from the timing controller IC.
Positive and negative DC voltages required for the gate driver can be realized with a simple configuration. For this reason, the mounting area of the power supply circuit and its peripheral circuits can be reduced, and the LCD substrate can be downsized and thus the liquid crystal display device can be downsized. In addition, since the DC-DC converter is not used, the cost of the liquid crystal display device can be reduced.

Further, in this power supply circuit, a positive and negative output voltage can be generated by switching the input voltage by a switching circuit, rectifying the switched input voltage to positive or negative, and then smoothing.

Further, according to the first and second output circuits using the shunt regulator, it is possible to generate a stable and accurate output voltage.

Further, in this switching circuit, the voltage amplified by the first switching element is used for driving the second switching element, so that the first switching element for switching the input voltage is compared with the case where the first switching element is directly driven by the PWS signal. The current driving capability required for the timing controller IC that outputs a signal can be suppressed.

This liquid crystal display device is suitable for downsizing and cost reduction, and is therefore suitable for mounting electronic equipment such as a printer.

A liquid crystal display device according to a second aspect of the present invention is a liquid crystal display panel, a source driver connected to a data line of the liquid crystal display panel, a gate driver connected to a scanning line of the liquid crystal display panel, the gate driver, And an LCD substrate connected to the source driver. The LCD substrate includes a timing controller IC and a power supply circuit that generates a positive and negative output voltage from an input voltage using a PWS signal output from the timing controller IC.

In this liquid crystal display device, on the LCD substrate, a positive and negative output voltage is generated from the input voltage by the power supply circuit using the PWS signal output from the timing controller IC.
Positive and negative DC voltages required for the gate driver can be realized with a simple configuration. For this reason, the mounting area of the power supply circuit and its peripheral circuits can be reduced, and the LCD substrate can be downsized and thus the liquid crystal display device can be downsized. As a result, it is possible to reduce the size of an electronic device such as a printer equipped with the liquid crystal display device. In addition, since the DC-DC converter is not used in the scan voltage generating power supply circuit, the cost of the liquid crystal display device can be reduced.

A liquid crystal display device according to a third invention is the liquid crystal display device according to the second invention, wherein the power supply circuit includes a switching circuit, a first rectifying / smoothing circuit, a first output circuit, a second rectifying / smoothing circuit,
A second output circuit. The switching circuit is driven by the PWS signal when the input voltage is input. The first rectifying / smoothing circuit rectifies and smoothes the output from the switching circuit and outputs a positive voltage. The first output circuit generates the positive output voltage from the positive voltage output from the first rectifying / smoothing circuit. The second rectifying / smoothing circuit rectifies and smoothes the output from the switching circuit and outputs a negative voltage. The second output circuit generates the negative output voltage from the negative voltage output from the second rectifying / smoothing circuit.

In this power supply circuit, a positive and negative output voltage can be generated by switching an input voltage by a switching circuit, rectifying the switched input voltage to be positive or negative, and then smoothing.

A liquid crystal display device according to a fourth invention is the liquid crystal display device according to the second or third invention, wherein the switching circuit is driven by a first switching element driven by the PWS signal and an output of the first switching element. And a second switching element for switching the input voltage.

In this switching circuit, the voltage amplified by the first switching element is used for driving the second switching element, so that the switching element for switching the input voltage is changed to PWS.
Timing controller IC that outputs PWS signal compared to direct drive by signal
The current driving capability required for the current can be suppressed.

A liquid crystal display device according to a fifth aspect of the present invention is the liquid crystal display device according to any one of the second to third aspects, wherein the first output circuit includes a first shunt regulator, and the second output circuit includes a second shunt regulator. It is characterized by including.

According to the first and second output circuits, a stable and accurate output voltage can be generated by the shunt regulator.

A liquid crystal display device according to a sixth aspect of the present invention is the liquid crystal display device according to the second to fifth aspects, wherein the liquid crystal display device is mounted on a printer.

This liquid crystal display device is suitable for downsizing and cost reduction. Therefore, when mounted on an electronic device such as a printer, the electronic device can be reduced in size and cost.

(1) Overall Configuration FIG. 2 is a schematic configuration diagram of a liquid crystal display device according to an embodiment of the present invention.

The liquid crystal display device includes a small display unit (LCD panel) and is mounted on an electronic device such as a printer. The liquid crystal display device includes an LCD panel 2, a source driver 3, a gate driver 4, an LCD substrate 5, and a main substrate 8.

The LCD panel 2 is a 2.5 inch small liquid crystal panel, for example. LCD panel 2
A plurality of scan lines arranged in the horizontal direction, a plurality of data lines arranged in the vertical direction, and a TFT having a gate connected to the scan line and a data line connected to the source or drain. is doing.

The source driver 3 is connected to a plurality of data lines of the LCD panel 2 and supplies a data voltage (data signal) to the data lines. The gate driver 4 is connected to a plurality of scan lines of the LCD panel 2, and a scan voltage (gate voltage) is applied to the scan line.
Supply.

The LCD substrate 5 includes a timing controller IC 6 and a gate voltage power supply circuit 9. The timing controller IC 6 supplies a horizontal synchronization signal and a vertical synchronization signal to the gate driver 4 and the source driver 3 based on the signal from the main board 8, respectively. The gate voltage power supply circuit 9 generates a DC voltage of ± 15 V necessary for the gate driver 4 using the PWS signal output from the timing controller IC6. Further, another voltage necessary for the gate driver 4 and a voltage necessary for the source driver 3 are generated by a power supply circuit (not shown) and output to the gate driver 4 and the source driver 3.

The main board 8 is a board on which a control circuit for controlling the entire operation of an electronic device such as a printer is mounted. The main substrate 8 controls the display on the LCD panel 2 by controlling the LCD substrate 5.

(2) Gate Voltage Power Supply Circuit FIG. 3 is an electric circuit diagram of the gate voltage power supply circuit 9 mounted on the LCD substrate 5. The gate voltage power supply circuit 9 includes a switching circuit 91, a first rectifying / smoothing circuit 92, a first output circuit 93, a second rectifying / smoothing circuit 94, and a second output circuit 95.

The switching circuit 91 includes a transistor Tr1 and a transistor Tr2. The base terminal of the transistor Tr1 is connected to the timing controller IC6 through the resistor R1, the capacitor C1, and the resistor R2, more specifically, to a pin (port) that outputs a PWS signal. The collector terminal of the transistor Tr1 is connected to a + 5V power source via a resistor R3, and the transistor T1 is connected via a resistor R4, a capacitor C2, and a resistor R5.
It is connected to the base terminal of r2. In the switching circuit 91, when the transistor Tr1 is switched by the PWS signal, the transistor Tr2 is switched by the transistor Tr1, and the DC voltage + 5V input through the choke coil L is switched by the transistor Tr2.

The first rectifying / smoothing circuit 92 mainly includes a diode D1 and a capacitor C4. The first rectifying / smoothing circuit 92 smoothes the positive DC voltage rectified by the diode D1 by the capacitor C4 and outputs the first voltage V1.

The first output circuit 93 includes a shunt regulator U1 and resistors R9, R10, and R11 that boost the output voltage of the shunt regulator U1. When the voltage obtained by stepping down the first voltage V1 with the resistor R8 is input to the cathode of the shunt regulator U1, the second voltage V2 is output from the shunt regulator U1. This second voltage V2 is applied to resistors R9, R10, R1.
1 is boosted by V2 * (R9 + R10 + R11) / R11 to generate an output voltage: + 15V. The first output circuit 93 includes a shunt regulator U1 and resistors R9 and R10.
, A capacitor C5 is provided to stabilize the + 15V voltage generated by R11.

The second rectifying / smoothing circuit 94 mainly includes diodes D2 and D3 and a capacitor C6. The diode D2 passes the positive voltage output from the capacitor C3 to the ground (ground potential). On the other hand, the diode D3 transmits the negative voltage output from the capacitor C3 to the output side. That is, only negative voltage is transmitted to the output side by the diodes D2 and D3. The capacitor C6 smoothes the negative voltage output from the diode D3 and outputs a third voltage.

The second output circuit 95 includes a shunt regulator U2 and resistors R13, R14, and R15 that boost the output voltage of the shunt regulator U2. When the voltage obtained by stepping down the third voltage V3 by the resistor R12 is input to the cathode of the shunt regulator U2, the fourth voltage V4 is output from the shunt regulator U2. This fourth voltage V4 is applied to resistors R13 and R14.
, R15 is boosted by V4 * (R13 + R14 + R15) / (R14 + R15) to generate an output voltage of −15V. The second output circuit 95 includes a shunt regulator U.
2. A capacitor C7 is provided for stabilizing the voltage of −15V generated by the resistors R13, R14, and R15.

(3) Effects In the liquid crystal display device 1, the gate voltage power supply circuit 9 is configured on the LCD substrate 5 using discrete components. A PWS signal output from the timing controller IC 6 mounted on the LCD substrate 5 is used as a switching control signal for driving the switching element of the gate voltage power supply circuit 9. That is, on the LCD substrate 5, a positive / negative output voltage (± 15V) is generated from the input voltage (+ 5V) by the gate voltage power supply circuit 9 using the PWS signal output from the timing controller IC6. For this reason, there is no need to provide a separate oscillation circuit for driving the switching element or to generate a switching control signal by processing a CPU clock signal or the like, and positive and negative direct current required for the gate driver 4 with a very simple configuration. A voltage (± 15V) can be realized. Therefore, the mounting area of the gate voltage power supply circuit 9 and its peripheral circuits can be reduced, and the LCD substrate and the liquid crystal display device can be downsized. Further, since the DC-DC converter is not used, the cost of the liquid crystal display device 1 can be reduced, and the cost of an electronic device such as a printer in which the liquid crystal display device 1 is mounted can be reduced.

In the gate voltage power supply circuit 9, the input voltage (+5 V) is applied to the switching circuit 91.
The output voltage can be positively or negatively rectified by rectifying the switched input voltage to positive or negative and then smoothing.

Further, in this switching circuit 91, the voltage amplified by the transistor Tr1 is used for driving the transistor Tr2, so that the PWS signal is compared with the case where the switching element for switching the input voltage (+ 5V) is directly driven by the PWS signal. The current drive capability required for the timing controller IC 6 to output can be suppressed.

Further, since the shunt regulators U1 and U2 are used for the first and second output circuits 93 and 94, a stable and accurate output voltage can be generated.

As described above, the liquid crystal display device 1 is suitable for downsizing and cost reduction, and is therefore suitable for mounting an electronic device such as a printer.

Schematic of the conventional liquid crystal display device. 1 is a schematic view of a liquid crystal display device according to an embodiment of the present invention. The electrical circuit diagram of the power supply circuit for gate voltages.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 LCD panel 3 Source driver 4 Gate driver 5 LCD substrate 6 Timing controller IC
7 DC-DC converter 8 Main board 9 Power supply circuit for gate voltage

Claims (6)

A liquid crystal display device mounted on a printer,
A liquid crystal display panel;
A source driver connected to a data line of the liquid crystal display panel;
A gate driver connected to a scanning line of the liquid crystal display panel;
An LCD substrate connected to the gate driver and the source driver, and including a timing controller IC and a power supply circuit that generates a positive and negative output voltage from an input voltage using a PWS signal output from the timing controller IC; With
The power supply circuit includes a switching circuit including a first switching element driven by the PWS signal and a second switching element driven by an output of the first switching element to switch the input voltage, and an output from the switching circuit A first output circuit including a first rectifying and smoothing circuit that rectifies and smoothes the output and outputs a positive voltage, and a first shunt regulator that generates the positive output voltage from the positive voltage output from the first rectifying and smoothing circuit A second rectifying / smoothing circuit that outputs a negative voltage by rectifying and smoothing the output from the switching circuit, and a second that generates the negative output voltage from the negative voltage output from the second rectifying / smoothing circuit. And a second output circuit including a shunt regulator. A liquid crystal display panel;
A source driver connected to a data line of the liquid crystal display panel;
A gate driver connected to a scanning line of the liquid crystal display panel;
An LCD substrate connected to the gate driver and the source driver, and including a timing controller IC and a power supply circuit that generates a positive and negative output voltage from an input voltage using a PWS signal output from the timing controller IC; ,
A liquid crystal display device comprising: The power supply circuit is
A switching circuit that receives the input voltage and is driven by the PWS signal;
A first rectifying / smoothing circuit for rectifying and smoothing an output from the switching circuit and outputting a positive voltage;
A first output circuit that generates the positive output voltage from a positive voltage output from the first rectifying and smoothing circuit;
A second rectifying / smoothing circuit for rectifying and smoothing an output from the switching circuit and outputting a negative voltage;
The liquid crystal display device according to claim 2, further comprising: a second output circuit that generates the negative output voltage from the negative voltage output from the second rectifying and smoothing circuit. The switching circuit is
A first switching element driven by the PWS signal;
A second switch driven by the output of the first switching element to switch the input voltage;
A switching element;
The liquid crystal display device according to claim 2, further comprising: 5. The liquid crystal display device according to claim 2, wherein the first output circuit includes a first shunt regulator, and the second output circuit includes a second shunt regulator. 6. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is mounted on a printer.

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