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Resonant Synchronous Rectification (2004)

Year: 2004
In non-isolated buck or isolated buck topologies, traditionally, fixed dead time scheme between the main switch and synchronous rectifier switch is used to avoid the cross conduction. However, the body diode has to freewheel the load current during the dead time. The voltage drop and reverse recovery associated with the synchronous rectifier body diode becomes a great percentage of the total synchronous rectifier power loss as lower output voltage. The basic idea of the proposed Resonant Synchronous Rectification is:

  1. Turn off the synchronous rectifier in ZCS by the resonance between leakage inductor and the capacitor which is in parallel with SR. As a result, there is no current going through the body diode after the SR turns off.

  2. By taking advantages of the slow drain-to-source voltage decreasing speed of SR which is determined by LC resonance, a voltage sensing scheme in driver detecting the zero voltage point can make SR turned on at the exact timing without any turn on loss and body diode conduction.

Based on this concept, a family of novel resonant synchronous rectifier DC/DC converters is derived. It features soft-switching and no body diode conduction, which is very promising for high switching frequency operation. The prototype is a 1MHz 1/16 brick version, which can achieve 1.2V/25A output with 85% efficiency.

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