Abstract: A DC to DC converter power supply for converting a varying unregulated DC voltage into a lower voltage regulated output. The DC to DC converter has a buck topology and includes a high frequency switch with a variable duty cycle, a regulating filter, a current inner control loop, a voltage outer control loop, a latching switch that provides a load bypass during startup, a logic circuit oscillator that controls the high frequency switch frequency duty cycle as a function of both the inner control loop current and the outer control loop voltage, and a circuit that taps the source voltage for a power input to the logic circuit oscillator during startup. The DC to DC converter admits a source voltage range of approximately 4:1 and provides a regulated fixed output voltage that ranges from approximately 30% of the source voltage at the lowest accommodated source voltage to approximately 5% of the source voltage at the highest accommodated source voltage.