Abstract: A switched-mode power supply providing high speed switch operation and high efficiency is disclosed. Faster switch turn-off is accomplished by means of an additional primary winding in the power supply's converter transformer which causes switching current to be diverted from the switch element when the oscillating switch transitions to the cut-off state. More rapid switch turn-on is achieved by shunting current from the regulation circuit of the power supply during initial switch turn-on in providing the entire switch control output of a blocking oscillator to the switch element. Power supply regulation is provided by an optical link including a photodiode coupled to a secondary of the converter transformer and a phototransistor which controls the input provided to the switch by the blocking oscillator.