Patent ID: 6671189
Filing Date: 2003-12-30
Classification: H02M,Y02B

Abstract:
A power converter comprising:an input terminal; an output terminal; a transformer having a primary side and a secondary side, said transformer further comprising a primary side winding connected to said input terminal and a secondary side winding connected to said output terminal; a primary side switch; a secondary side switch; a slave control unit controlling switching of said secondary side switch; a master control unit controlling switching of said primary side switch; and a secondary current sense detecting said secondary current in said secondary side switch, said primary side switch and said secondary side switch being configured to be switched on and off alternately; wherein said switching of said secondary side switch is accomplished depending on a secondary current detected in said secondary side switch, and wherein said primary side switch and said secondary side switch are switched on during a zero voltage switching condition; wherein said slave control unit further comprises a comparator and a set/reset flip flop, wherein said secondary current sense conveys an output signal into said comparator when said secondary current becomes negative, wherein said comparator compares said output signal of said secondary current sense to a current reference level and outputs a switching signal to said set/reset flip flop when said output signal of said secondary current sense exceeds said current reference level, wherein said set/reset flip flop switches said secondary side switch when said switching signal is received and wherein said current reference level is given by the following equation: Ireverse=(Vin+Vo*N)*{square root over ( )}[(Cds1+Cds2/N2)/LT1C]wherein Ireverse is said current reference level, LT1C is an inductance of said secondary side winding of said transformer, Cds1 is an intrinsic capacitance of said primary side switch, Cds2 is an intrinsic capacitance of said secondary side switch, Vin is an input voltage, Vo is an output voltage and N is a winding ratio between said primary and said secondary side windings.