Patent ID: 7598627

Claim:
A switch-mode power supply for selectively providing power from a main power source and a standby power source to an electronic device, comprising: a signal input for receiving a control signal; a first transistor having a gate connected to the signal input for receiving the control signal, a drain acting as a voltage output, and a source connected to the standby power source; a second transistor having a gate, a drain acting as the voltage output, and a source connected to the main power source; a driving circuit and a switching circuit connected between the signal input and the gate of the second transistor in parallel such that when the driving circuit detects the first transistor is switched off, the gate of the second transistor is immediately pulled up to open the second transistor by the switching circuit, and when the driving circuit detects the first transistor is switched on, the gate of the second transistor is immediately pulled down by the driving circuit to close the second transistor.