Patent ID: 7751208

Claim:
A controller for a resonant discontinuous forward converter (RDFC), said converter including a transformer with a core and primary and secondary matched polarity windings and a switch to, in operation, cyclically switch DC power to said primary winding of said transformer, said converter arranged to resonate on a primary side of said converter to reset flux of said core each time said switch is off during each cycle of said DC power switching, said converter further having a DC output coupled to said secondary winding of said converter, said controller having a primary sense input to sense a primary winding signal, said primary winding signal representing a voltage across said primary winding or across an additional winding coupled to said primary winding, and wherein said controller is configured to switch on said switch in response to detection of a reduction in a rate of change of said primary winding signal below a threshold, adjacent a substantially minimum value in an operational cycle of said sensed primary winding signal to convey power to said DC output; said primary sense input arranged to couple to said primary or additional winding via a capacitor to sense said primary winding signal, and the controller comprises a circuit for controlling said switch in response to said resonance of said RDFC, said circuit arranged to receive at said input current from said capacitor and having said input arranged to have an impedance such that said current received at said input is substantially proportional to said rate of change of said primary winding signal when said switch is on and when said switch is off and arranged to output signals for controlling switching on and off of said switch on the basis of said received current, said signals comprising a first signal representing a rising primary winding signal and a second signal representing a falling primary winding signal.