US Patent 7821797 Isolated DC-DC converter

A switching circuit arranged to switch the input of an input power supply is connected to a primary winding of a transformer at a primary side of the transformer. A digital control circuit including a switching controller arranged to output control pulses to the switching circuit and a rectifying/smoothing circuit connected to secondary windings of the transformer are disposed at a secondary side of the transformer. The digital control circuit outputs the control pulses via a pulse transformer, calculates the input power-supply voltage on the basis of the on-duty cycle of the control pulses, the output voltage, and the ratio of the number of turns of the primary winding to the number of turns of the secondary windings of the transformer, and performs converter control in accordance with the calculated input power-supply voltage.