 MOSFET heating and ZVS with half-bridge
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IamSmooth
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Sun Aug 08 2010, 05:21AM
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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
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I have studied the the path the current takes through the switch and the freewheeling diodes during modes 1 through 4 during mosfet switching. Normally, this unit can take 40-50A and get slightly warm. I tried getting the tuning more precise so the current and voltage were zero at the same time. I found that at a range of 2-4A the mosfets were getting hot! I can only guess that the current was getting conducted through the FWDs. I solved the problem by slightly detuning the inverter so the current lagged the voltage by a few degrees.
Now I am measuring the voltage and current on the load. It could be that what I think is slightly lagging may actually be closer to ZVS if I were to make the measurements directly across the drain-source.
So, why did it the mosfets get hot at such a low current? The current should go through the FWDs if I am tuned above or below resonance, so would they get hot if the current led the voltage?
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