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Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
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Posts: 108
When cranking up the volts on my variac of the half bridge, the voltage on the gate of the first transistor starts to decrease cuasing shut down and failure to my brick at high power levels.Ive tried it with mosfets also and it still does the same thing and there is no ringing or paracitic oscillation showing on my scope. Is anyone familiar with this?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
If you are following the schematic exactly it should work. Unless there are other suggestions, I would suggest swapping out new mosfets and new bypass capacitors. You can check if the mosfets are good; checking the capacitors is probably not easy. I just put in new ones. Make sure you are using the components I used on the schematic. If you use the wrong capacitors they will fail. Sometimes suddenly; more likely they will fail slowly and subtly.
Make sure you have the body diodes in place in the correct direction.
I am curious what happens if you remove the tank capacitor/coil to your waveform. If the gate voltage is going down I am thinking there is a short developing on the load end.
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
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Posts: 108
Ive tried changing the mosfets and caps and i also removed the tank from the load but it stil does the same thing. Do i need body diodes if the mosfet already has an internal diode? The bypass caps i have are rated .68 uf 1000vollts, Are these ok?
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Induction heater
