Patent ID: 7773392

Claim:
An isolated switching power supply apparatus comprising: a power transformer including at least a primary winding and a secondary winding; at least one power switch arranged to switch current flowing through said primary winding; a rectifying circuit and a smoothing circuit connected to said secondary winding, wherein control is provided such that a controlled variable of output approaches a target value by controlling turning on and off of said power switch; a timing signal output circuit, provided on the secondary side, arranged to output an output voltage to cause said power switch to perform a switching operation of one of turn-on or turn-off, based on a change in said controlled variable; a timing signal transfer circuit arranged to transfer a timing signal defined only by a level change of the output voltage of the timing signal output circuit from the secondary side to the primary side in an isolated manner; a power switch control circuit, provided to the primary side, arranged to cause said power switch to perform switching operations based on said timing signal.