Abstract: A variable-frequency pulse-width-modulated D-C to D-C converter allows operation at very high frequencies with minimal power transistor switch transient turn-on losses. A frequency control scheme is utilized wherein the controller of the converter causes switching to occur when the voltage across the power transistor switch is near zero volts. In addition to reducing transient turn-on losses, zero-voltage switching reduces noise generation in the circuit and simplifies the power transistor drive requirements.Other characteristics of opimal power transistor switch utilization are met in addition to turning the switch on under a zero potential. Maximum peak voltage across the switch is limited to approximately the ouput or input voltage level depending on the configuration used. In addition, peak and average currents through the switch are proportional to output power requirements and turn off transient dissipation is held to a minimum.