US 5,206,800 AGranted

Zero voltage switching power converter with secondary side regulation

AssigneeAstec International Limited

InventorDavid A. Smith

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Abstract

A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch and to regulate the output voltage is disclosed. The power converter includes a transformer having a primary winding and a secondary winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch. A second switch means is connected in series with the secondary winding of the transformer and is operated to prevent the loading effects of the secondary from interrupting the creation of the zero-voltage switching condition. A secondary side regulation circuit is included to both regulate the output voltage and to prevent the loading effects of the secondary circuit from interfering with zero-voltage switching in the primary circuit.

In a converter having a transformer including a primary winding and a secondary winding, said secondary winding coupled to an output load, and having a primary switch means connected in series between said primary winding and a voltage source, said primary switch means causing energy from said voltage source to be stored in said transformer when said primary switch means is closed during an ON period and causing said energy to be released from said transformer when said primary switch means is open during an OFF period, circuitry for utilizing the energy stored in said transformer to reset the core of said transformer during said OFF period of said primary switch means, to minimize the voltage stress on said primary switch means when said primary switch means closes, and to regulate the output voltage at said output load, said circuitry comprising:

a storage capacitor;
a first switch means coupled in series with said storage capacitor, the series combination of said storage capacitor and said first switch means coupled in parallel with one of said transformer windings;
a second switch means coupled in series with said secondary winding of said transformer;
and
a switch control means for operating said first and second switch means in relation to the operation of said primary switch means, said switch control means closing said first switch substantially when said primary switch means opens and opening said first switch means prior to when said primary switch means closes to create a zero-voltage switching condition on said primary switch means when said primary switch means next is caused to close, said switch control means including a secondary-side control means for controlling said second switch means and for regulating the output voltage of said converter, said secondary-side control means closing said second switch means no earlier than when said primary switch means closes and opening said second switch means before said first switch means closes, said secondary-side control means further for controlling the duration said second switch means is closed such that the value of said output voltage is regulated within a predetermined voltage range.

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Abstract

Claims13