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Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
Also you should use one gate resistor per fet, and depending on application, current sharing resistors like those 0.1´s seen in class ab audio amplifier output stages.
that your scope flips when you try scoping your circuit in operation also is a quite strong sign that something is wrong, any time you have enough emi/rfi to make a scope mad, theres something wrong with the circuit, usually called stray inductance as in too long leads that act like antennas and messes un gate waveforms and cause voltage and current spikes that can kill even the biggest baddest most indestructible fet/igbt.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
HFsstc-freak wrote ...
Also you should use one gate resistor per fet, and depending on application, current sharing resistors like those 0.1´s seen in class ab audio amplifier output stages.
that your scope flips when you try scoping your circuit in operation also is a quite strong sign that something is wrong, any time you have enough emi/rfi to make a scope mad, theres something wrong with the circuit, usually called stray inductance as in too long leads that act like antennas and messes un gate waveforms and cause voltage and current spikes that can kill even the biggest baddest most indestructible fet/igbt.
Hmm, the currents were not that big (few tens of A max peak) nor the frequency (50kHz). I really have no idea where my scope gets all the interference but it gets it with ANY higher power switching circuit I've ever built, even ones with slow-ish gate drivers. Well I guess I need a new scope!
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Too fast gate drive kills FETs
