Discharging apparatus for liquid crystal display
View Patent ↗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.
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.