Patent ID: 6498734
Filing Date: 2002-12-24
Classification: H02M

Abstract:
A power supply unit comprising:a transformer having a primary winding connected in series to a D.C. power supply; a first switching element connected in series to said primary winding; a first rectifier element connected in series to a secondary winding of said transformer; a choke coil connected in series to said first rectifier element; a second switching element connected in series to said choke coil; a first smoothing circuit connected in series to said second switching element; a second rectifier element connected in parallel with said first rectifier element and said secondary winding; a control circuit for controlling a conducting period of said first switching element responsive to an output voltage of said first smoothing circuit; a third switching element connected in series to said choke coil; a second smoothing circuit connected in series to said third switching element; and a divider control circuit having a first input terminal receiving any of an input voltage and an output voltage of said second smoothing circuit, for extracting an electric current only of a give period from a current passing through said choke coil, and for controlling a conducting period of said third switching element.