Switched-mode power supply with output post-regulator

Abstract

A switched-mode power supply provides a plurality of directly regulated DC output voltages. The power supply includes a first inverter-coupled transformer for providing first and second DC output voltages, with a feedback loop provided from a first output to the inverter for regulating the first DC output voltage. A second transformer is coupled across the first and second output lines of the first transformer and is further coupled across the second output lines by means of a switching regulator circuit including a second feedback loop for regulating the second DC output voltage. By proper selection of the number of turns of the second transformer, the regulator is capable of either substantially increasing the second output voltage when the switching device is on while lowering the output voltage very little when the switching device is off, or increasing the second output voltage very little with the switching device on while substantially lowering the output voltage when the switching device is off. This permits the use of a large turns ratio in the second transformer in combination with smaller diodes and transistors which carry current equal to the output current divided by the second transformer's turns ratio. Reduced output current provides more efficient power supply operation, while the use of smaller semiconductors reduces power supply cost.