Abstract: A push-pull converter, coupled through an isolation transformer to a crowbar circuit for controlling an isolated output voltage across an output capacitor, has a compact circuit arrangement with a minimal number of components. The switching devices of the push-pull converter have integrated, ultra-fast anti-parallel diodes. The crowbar circuit is a voltage-controlled bi-directional switch coupled between the transformer and the output capacitor. The converter is controlled in an output-voltage-on mode by turning on and off the first switching device, and in an output-voltage-off mode by applying a gating signal to the second switching device sufficient to both activate the crowbar circuit and discharge the output capacitor for very fast isolated output voltage turn-off. In addition, a primary-side circuit comprising a switch and a resistance can be used to avoid excessive residual output voltage build-up.

Abstract: A single power supply circuit, including a push-pull input converter stage and a voltage-controlled latch circuit output stage isolated from each other by a transformer, provides both voltage gridding and biasing functions in, for example, an x-ray tube application. In the gridding mode, a first voltage level supplies the push-pull converter to provide an output voltage that is sufficiently high to trigger the voltage-controlled latch circuit and thereby provide grid control via a grid control electrode. In the biasing mode, a lower voltage level supplies the push-pull converter such that the output voltage is insufficient to trigger the voltage-controlled latch circuit. As a result, a resistive voltage divider provides a predetermined biasing voltage on a bias control electrode.

Abstract: A forward converter, having a single switching device, is coupled through an isolation transformer to a crowbar circuit and an output capacitor for controlling the isolated output voltage turn-off. The crowbar circuit, including a trigger device and a resistor, is coupled between the transformer and the output capacitor. The conduction times of the converter switching device are controlled to regulate the energy stored in the transformer and to generate a reverse voltage having a predetermined amplitude. During the output voltage-on mode, the amplitude of the reverse voltage swing is controlled to be sufficiently low such that the converter operates as a conventional forward converter. For output voltage turn-off, the conduction time of the switching device is controlled to obtain a voltage swing of sufficient magnitude to trigger the crowbar circuit, and thus rapidly discharge the output capacitor.

Abstract: 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.