Patent ID: 7990373
Filing Date: 2011-08-02
Classification: G09G

Abstract:
1. A power supply circuit for a liquid crystal display device, comprising: a switch control circuit for receiving a control signal from an external control circuit, the control signal controlling the turning on or turning off of the switch control circuit; a first DC/DC converter for adjusting a direct current voltage from an external circuit, and outputting an output voltage to the switch control circuit and the external control circuit; and a second DC/DC converter for receiving the output voltage via the switch control circuit and transferring the output voltage to working voltages of the liquid crystal display device; wherein the switch control circuit comprises a P-channel field effect transistor, a first resistor, a second resistor, a third resistor, a capacitor, and a NPN transistor; wherein a source electrode of the P-channel field effect transistor is connected to the first DC/DC converter for receiving the output voltage, a drain electrode of the P-channel field effect transistor is connected to the second DC/DC converter for providing the output voltage to the second DC/DC converter, a gate electrode of the P-channel field effect transistor is connected to a collector electrode of the NPN transistor via the second resistor, a base electrode of the NPN transistor is configured for receiving the control signal via the first resistor, an emitter electrode of the NPN transistor is grounded, the third resistor is connected between the source electrode of the P-channel field effect transistor and the collector electrode of the NPN transistor, and the capacitor is connected between the source electrode and the gate electrode of the P-channel field effect transistor; wherein, when the NPN transistor is turned on under the control of the control signal, the P-channel field effect transistor is turned on such that the output voltage is provided to the second DC/DC converter via the P-channel field effect transistor; and when the NPN transistor is turned off under the control of the control signal, the output voltage output by the first DC/DC converter is provided to the gate electrode of the P-channel field effect transistor via the third resistor and the second resistor to turn off the P-channel field effect transistor so as to prevent the output voltage from being provided to the second DC/DC converter.