Zero-voltage switching power converter with lossless synchronous rectifier gate drive

摘要

A converter operating in a resonant mode of operation is used as an off-line switching power supply operating with a high power density. A drive arrangement and operative scheme for driving the power switching transistors limits the dissipation losses within the power switching transistors. Drive circuitry drives two power switching transistors with unequal duty cycles having conducting durations such that the sum of the conduction intervals substantially equals the combined switching period of the two power switching transistors. These conducting intervals are separated by very short dead time intervals controlled by the differing turn-on and turn-off times of the two power switching transistors. The short interval between alternate conductions of the two power switching transistors is sufficient in duration to allow zero voltage turn on of the power switching transistors but short enough in duration to minimize power loss and conducted noise. In the illustrative embodiment the dead time is at least an order of magnitude less than the time interval of the shortest duty cycle. Regulation of the output of the converter is attained by adjusting the ratio of the first and second duty cycles or conducting intervals.PPA Synchronous rectifier, suitable for a converter having minimum dead time between conduction of the two switching devices, comprises MOSFET rectifying devices which are driven in a zero voltage switching mode so that the charging and discharging of the MOSFET gate capacitances are lossless.