Switching dc power supply

Abstract

A transformer has a primary winding connected between a pair of dc input terminals via a voltage regulator switch, and a secondary winding connected between a pair of dc output terminals via a rectifying and smoothing circuit. The dc output voltage being applied to the load from the dc output terminals is detected, and the detector output voltage dually divided, to provide two feedback signals of different magnitudes. One of these feedback signals is used by a mode selector circuit to provide a mode select signal for causing the voltage regulator switch to be driven continuously under normal load, and at intervals under light load. Delivered to a conduction terminator circuit, the other feedback signal is thereby used to provide conduction terminator pulses for terminating conduction through the voltage regulator switch. A conduction initiator circuit responds both to the mode select signal and to a signal indicative of the conduction and nonconduction of the voltage regulator switch, to initiate conduction therethrough upon lapse of a preassigned length of time following the end of the previous conducting period. Although the nonconducting periods of the voltage regulator switch are thus fixed, its conducting periods are variable with the results of comparison of a switch current detect signal and the second recited feedback signal.