Patent ID: 6980441

Claim:
A forward converter, comprising: a transformer having a primary winding and a secondary winding; a power switch connected in series with said transformer and coupled to an input power source, said power switch capable of being alternately switched between an on period and an off period as a function of a PWM signal comprising pulses generated by a PWM circuit and such that an AC voltage is generated across said secondary winding in response thereto; an output filter operative to provide a substantially constant DC voltage to an output load; a forward rectifier having a control input and being operative to provide a forward conduction path between said secondary winding and said output filter during said on period; a free-wheeling synchronous rectifier having a control input and being operative to provide a second conduction path for maintaining current to said output filter during said off period; and a control circuit coupled to said control input of said free-wheeling synchronous rectifier for controlling the state thereof, said control circuit receiving a clock signal varying between an upper voltage and a lower voltage and having a frequency equal to or greater than said PWM signal, comprising: a reference circuit for generating a PWM reference signal by causing the trailing edge of said PWM signal to decrease in voltage at a predetermined rate such that said PWM reference signal drops below and remains below said lower voltage if the next pulse of said PWM signal has not been generated; a comparator circuit for comparing said PWM reference signal to said clock signal and for generating an output signal as a function thereof such that said output signal is on when said PWM reference signal is below said lower voltage; and a driver circuit responsive to said output signal and said PWM signal so as to turn off said free-wheeling synchronous rectifier when said output signal is on and so as to enable said PWM signal to control said free-wheeling synchronous rectifier when said output signal is off.