Patent ID: 8488343

Claim:
A switching mode power supply apparatus, comprising: a transformer having a primary coil connected to a power supply source and a secondary coil connected to an output circuit; a main switch to control power supplied from the power supply source to the primary coil of the transformer; a passive clamp circuit coupled to the main switch and the primary coil of the transformer to perform a clamping operation so as to suppress a voltage stress of the main switch; a switch coupled to the passive clamp circuit; and a control circuit to switch on the switch in a normal mode to enable the clamping operation of the passive clamp circuit and to switch off the switch in a standby mode to disable the clamping operation of the passive clamp circuit such that power is consumed in the passive clamp circuit, the switch always being on in a normal mode and always being off in a standby mode, wherein the main switch controlling the supplied power is independent with the switch at both of the standby mode and the normal mode, the standby mode of the switching mode power supply apparatus is a mode consuming a minimum non-zero power, and the main switch is always switching on/off for maintaining a turn-on state of the switching mode power supply apparatus in both of the normal mode and the standby mode.