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Turn-off loss in H-Bridge converter MOSFET resulting from ZVS turn-on of complimentary device

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Junior Member level 1
Jul 17, 2018
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Generally ZVS turn-on of MOSFET is considered as a good feature in power converters. In H-bridge converters, the MOSFETs in a switching leg operate in complimentary manner. So, when one device is undergoing ZVS , it is certain that the complimentary device turn-off happened when it was carrying a non-zero current. Because, only after the device is completely off, the diode in the turning on device can conduct. This would result in turn-off loss in the device. Why ZVS turn-on is still considered as favorable feature even though it results increased turn-off loss in complimentary device.

Tuning the "handoff" timing is key interest in power stage design. Can be done "ballistic" or some folks will servo to a minimal SW undershoot to get "just enough" current to finish the job (Near Zero Current switching).

Cross conduction is bad,. Momentary open is bad, there is a happy place in between.

turn off losses in a ZVS designed H bridge are largely governed by the speed of the gate drive at turn off - unless the gate can go from 10V to 0v in <= 30nS you will not get low loss turn off, additional caps across mosfets are sometimes used to reduce dv/dt at turn off, having enough fwd current in the mosfet at turn off is essential to get a full voltage transition so that the other mosfet can turn on under ZVS - for just enough energy - the timing of the turn on is critical ... for excess energy you get a larger time window for turn on ...

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