Patent ID: 8654548

Claim:
A primary-side output voltage sensing apparatus for a flyback power converter comprising: a transformer comprising: a primary winding operatively connected to an input voltage, and a secondary winding operatively connected to a diode wherein the diode is operatively connected to a load circuit; a switching circuit operatively connected to the primary winding and configured to selectively connect an end of the primary winding to ground; a pulse width modulation (PWM) controller configured to produce a periodic PWM waveform for opening and closing the switching circuit during each cycle of the PWM waveform; a timing circuit including a counter and configured to: start the counter when the PWM controller opens the switching circuit during the Nth PWM cycle, wherein N is a positive integer; and stop the counter upon receiving a stop pulse; wherein a value stored in the counter represents a time duration of a diode conduction interval; a sensing circuit operatively connected to the primary winding and configured to generate the stop pulse by comparing a measurement of a voltage on the primary winding to a threshold voltage; a strobe circuit adapted to generate a voltage-sampling strobe during the (N+1)th PWM cycle based at least in part on the value stored in the counter; a sample and hold circuit operatively connected to the primary winding and the strobe circuit and configured to sample a voltage sample when triggered by the voltage-sampling strobe.