Push-pull power converter with crowbar circuit for very fast output voltage turn-off

摘要

A forward converter useful in a power supply utilizing an isolation transformer includes a crowbar circuit and control such that turn-off by discharging an output capacitor is made advantageously faster than conventional circuits. The forward converter has a push-pull arrangement of two switching devices. For operation in the output voltage-on mode, the forward converter transfers energy in a peak forward converter mode with the first switching device being turned on and off. For output voltage turn-off, the crowbar circuit is activated by turning on the second switching device which results in a reverse voltage at the secondary winding of the isolation transformer. The reverse voltage is superimposed on the converter output voltage, the sum of the converter output voltage and the reverse voltage being imposed across the crowbar circuit. If the sum of the converter output voltage and the reverse voltage exceeds the breakover voltage of the crowbar circuit, the output capacitor discharges rapidly through the crowbar circuit and the transformer secondary winding.