 Timing issue with parallel mosfets
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IamSmooth
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Wed Jul 21 2010, 03:16AM
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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
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I have a pair of mosfets (IXFN56N90P) for each leg of my half-bridge inverter. The gate is supplied with a +/-15v square wave with 18v zener clamps. The signal goes through a 1% 10R resistor and then a ferrite bead before hitting the gate. The wire lengths are very similiar and short.
I notice that the sinusoidal current waveform "skips" a little bit at all power settings. It is not a smooth singular tracing. I disconnected one of the gate drives so I was only now running one mosfet per leg of the inverter. Now the signal is solid and clean.
I don't know if this is a slight variation in the mosfet die during production. I don't know if my gate signals are slightly out of phase. Any suggestions?
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Myke
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Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
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This one guy who designs pulse power circuits for accelerators showed me a board with each MOSFET having their own gate driver. You might want to try that? Have you tried putting in a lower freq and see if it skips at all?
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GeordieBoy
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Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
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Is probably HF oscillation of the load current between paralleled MOS devices. This is quite common if they linger in the linear region too long. It's hard to say without seeing scope plots of the drain current for both devices though.
-Richie,
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