Patent ID: 6711035
Filing Date: 2004-03-23
Classification: H02M,Y02B

Abstract:
A switching power supply in which energy is supplied to a smoothing choke coil from a secondary winding of a transformer via a rectifier element when a switching element turns on, while the energy stored in the choke coil is fed to a load through a freewheeling element when the switching element turns off, in which at least said freewheeling element includes a freewheeling switch element which operates synchronously with said switching element, said the switching power supply comprising:an unidirectional conductible element which is connected in parallel with reverse polarity across said freewheeling switch element; and a surge voltage prevention circuit which detects a timing for a current to flow in a direction in which said unidirectional conductible element conducts by detecting a falling edge of a pulse drive signal fed to said switching element when an operation stoppage signal to said switching element is outputted, and then turns off the freewheeling switch element at this timing.