Liquid crystal display with alternating current off control circuit

1. A liquid crystal display, comprising:

a power supply circuit;

a scaler; and

an alternating current off control circuit;

wherein when an associated external alternating current voltage suddenly drops to zero, the alternating current off control circuit is configured to output a corresponding control signal to the scaler, and the scaler is configured to control the liquid crystal display to shut down according to a direct current off procedure;

wherein the alternating current off control circuit comprises an input terminal, a first resistor, a second resistor, a capacitor, a diode, a switch circuit, a control terminal and an output terminal, the input terminal is connected to the power supply circuit and receives an external alternating current voltage via the power supply circuit, an anode of the diode is connected to the input terminal via the first resistor and connected to ground via the second resistor, a cathode of the diode is connected to ground via the capacitor and connected to the switch circuit, the switch circuit is connected to a direct current voltage source via the control terminal, and the switch circuit is connected to the scaler via the output terminal;

wherein the first resistor, the second resistor, the capacitor and the diode transform the external alternating current voltage into a direct current voltage;

in a situation that the power supply circuit operates normally, the switch circuit is turned off;

in a situation that the external alternating current voltage drops to about zero volts, the switch circuit is turned on, and the decreased direct current voltage is provided to the scaler via the output terminal;

wherein an inverter is configured to receive direct current voltages from the power supply circuit, control signals from the scaler, and transform the direct current voltages into a high-frequency alternating current voltage;

wherein when the scaler receives a decreased direct current voltage from the alternating current off control circuit, the scaler transmits a first shutting down signal to the inverter to shut down the inverter, and after a first time, the scaler stops transmitting video signals to a liquid crystal display panel, and after a second time, the scaler transmits a second shutting down signal to shut down the power supply circuit.

2. The liquid crystal display of claim 1 , wherein the switch circuit is a PNP bipolar transistor, a base electrode of the PNP bipolar transistor is connected to the cathode of the diode, an emitter electrode of the PNP bipolar transistor is connected to the control terminal, and a collector electrode of the PNP bipolar transistor is connected to the output terminal.

3. The liquid crystal display of claim 1 , wherein

the switch circuit is a P-channel metal-oxide-semiconductor field effect transistor, a gate electrode of the P-channel metal-oxide-semiconductor field effect transistor is connected to the cathode of the diode, a source electrode of the P-channel metal-oxide-semiconductor field effect transistor is connected to the control terminal, and a drain electrode of the P-channel metal-oxide-semiconductor field effect transistor is connected to the output terminal.

4. The liquid crystal display of claim 1 , wherein the alternating current off control circuit is packaged in the power supply circuit.

5. The liquid crystal display of claim 1 , wherein the alternating current off control circuit is packaged in the scaler.

6. The liquid crystal display of claim 1 , wherein the first time is about 50 ms.

7. The liquid crystal display of claim 1 , wherein the second time is about 30 ms.