A soft-switching circuit for achieving zero-voltage-transition (ZVT) type commutation in switching power converters includes a magnetic feedback circuit for achieving substantially zero voltage turn on of the active power switches and for achieving zero voltage turn off of the passive power switches...http://www.google.com/patents/US5477131?utm_source=gb-gplus-sharePatent US5477131 - Zero-voltage-transition switching power converters using magnetic feedback
