Abstract: Resonant DC to DC flyback converter topologies having one or more transformers and a primary side resonant subcircuit are optimally controlled by providing independently derived duty cycles for driving the main transformer and resonant semiconductor switches to prevent cross-conduction thereof and minimize reverse recovery losses.

Abstract: Resonant DC to DC power converter topologies include a PWM-controlled flyback converter having a single transformer and a primary side resonant subcircuit that is optimally controlled to minimize reverse recovery losses. A second transformer may be added wherein the primary windings are connected in series, the first transformer having substantially greater inductance than the second transformer to more efficiently transfer energy over a wide range of output load conditions. A combined forward-flyback resonant converter utilizing a load-side buck loop for increased power delivery performance and start-up circuitry for initial power connection of the converter to a voltage source utilizing a hysteresis protection circuit are also disclosed.

Abstract: A printed circuit board apparatus includes a handle which has an extension plate which extends into an optical switch so as to prevent communication between an optical emitter and optical receiver. To remove the printed circuit board apparatus from its associated rack housing, rotation of the handle is first required which moves the plate and which causes the detector to go HIGH and signal to a telecommunications system that the board is soon to be removed so that a graceful switch can be made from that board to a redundant copy thereof. The printed circuit board apparatus further includes a deflectable lever which contacts to ground the rack housing upon inserting the printed circuit board apparatus into its associated rack housing so as to provide electrostatic discharge protection.