Abstract: A switching power converter comprising an inductor and one or more switches and configured to operate in a discontinuous operating mode comprises a clamp circuit connected to the ends of the inductor for trapping energy in the inductor during a clamp period. The clamp circuit comprises a first and a second clamp switch connected in series, the clamp circuit arranged and configured to block a voltage of either polarity when both switches are OFF; conduct a current of either polarity when both switches are ON; conduct uni-directionally in one direction when one of the clamp switches is ON; and conduct uni-directionally in the other direction when the other one of the clamp switches is ON. A controller turns the one or more switches ON and OFF to transfer energy from the input to the inductor and from the inductor to the output during an energy transfer phase.

Abstract: A primary-side sampled feedback system includes a sample acquisition phase during which the voltage across the clamp capacitor is sensed as a measure of the primary-reflect output voltage. One end of the clamp capacitor is ground-referenced during the sample acquisition phase. The sample circuitry, which may include a transformer-coupled input for receiving the gate drive of the secondary switch, may use primary side, secondary-side, or primary and secondary side signals to generate the sample acquisition control pulse and clamp switch drive signal. The sample acquisition control pulse occurs when the secondary current reaches its minimum or zero.