Abstract: A high-efficiency programmable power supply including a linear regulator and a switching pre-regulator. The switching pre-regulator monitors the voltage drop across the series pass regulator pass transistor and maintains a predetermined voltage drop thereacross. The programmable power supply output voltage is varied according to a digital signal applied to the linear regulator. The switching pre-regulator, in providing a generally constant voltage drop across the linear regulator pass transistor, increases efficiency of the power supply by reducing excess voltage which appears at the input of the linear series pass regulator to a minimum level below which the linear regulator can operate. Therefore, the power supply according to the present invention maintains high efficiency over a wide range of selectively programmed output voltages.