Discharging apparatus for liquid crystal display

• US 6,903,734 B2
• Filed: 06/29/2001
• Issued: 06/07/2005
• Est. Priority Date: 12/22/2000
• Status: Expired due to Term

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Philips LCD Company Limited (LG Display Co., Ltd.)
• Inventors: Eu, Jung-Taeck
• Primary Examiner(s): Liang, Regina
• Assistant Examiner(s): Nguyen, Jennifer T.
• Application Number:
  US09/893,985
• Publication Number:
  US 20020080133A1
• Time in Patent Office: 1,439 Days
• Field of Search: 345/211, 345/212, 345/213, 345/214, 345/87, 345/90, 345/92, 345/96, 345/98, 345/100
• US Class Current: 345/211
• CPC Class Codes: G09G 2310/0245 Clearing or presetting the whole screen independently of waveforms, e.g. on power-on G09G2310/063 takes precedence
• CPC Class Codes: G09G 2320/0257 Reduction of after-image effects
• CPC Class Codes: G09G 2330/027 Arrangements or methods related to powering off a display
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A discharging apparatus for a liquid crystal display is provided for substantially reducing a residual image upon power-off. In the apparatus, a gate driver integrated circuit selectively applies first and second gate voltages to gate lines of the display. A discharge circuit is coupled to the gate driver integrated circuit and senses a power-off state of a power supply line. When a power-off state is sensed, a short-circuit if formed between the first gate voltage supply line and the second gate voltage supply line, thereby discharging voltages on the gate lines. Accordingly, a gate low voltage relative gate high (pixel turn-on) voltage is discharged upon power-off to define a discharge path via the gate line, thereby rapidly discharging electric charges charged in the liquid crystal display panel.

Claims

1. A discharging apparatus for a liquid crystal display including a plurality of liquid crystal pixel cells, each of the liquid crystal cells being arranged at an intersection between one of a plurality of gate lines and one of a plurality of data lines, and switching devices for driving the liquid crystal cells in response to a signal from each gate line, the discharging apparatus comprising:

a first gate voltage supply line;

a second gate voltage supply line;

a power supply line;

gate driver circuitry for selectively applying to the gate lines first and second gate voltages supplied from the first and second gate voltage supply lines, respectively; and

a discharge circuit for sensing a power-off condition of the power supply line to short-circuit the first gate voltage supply line and the second gate voltage supply line when the power-off condition is sensed, thereby discharging voltages on the gate lines.

2. The discharging apparatus according to claim 1, wherein the first gate voltage is a positive gate high voltage, and the second gate voltage is a gate low voltage, and the gate low voltage is negative relative the positive gate high voltage.

3. The discharging apparatus according to claim 2, wherein said discharge circuit includes:

power-off sensing circuitry for sensing the power-off condition of the power supply line; and

a switching device for short-circuiting the first and second gate voltage supply lines upon power-off in response to a control signal from the power-off sensing circuitry.

4. The discharging apparatus according to claim 3, wherein said discharge circuit includes:

a capacitor for charging to a desired voltage when a power voltage is being applied from the power supply line and discharging the charged desired voltage upon the power-off condition; and

a switching control device for controlling the switching device in response to the desired voltage discharged from the capacitor.

5. The discharging apparatus according to claim 4, wherein the desired voltage charged in the capacitor comprises a voltage difference between the gate high voltage and the power voltage, and the capacitor discharges the desired voltage upon the power-off condition.

6. The discharging apparatus according to claim 4, wherein said switching device is a NPN-type transistor, and said switching control device is a PNP-type transistor.

7. The discharging apparatus according to claim 1, wherein the discharge circuit is provided on a printed circuit board and connected to the gate driver circuitry.