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Registered Member #1617
Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139
Hi all,
I've built a more compact h-bridge for my sstc, and wound a new gate drive transformer, with 4 secondarys to drive all 4 fets from the one GDT. The problem is though, there is about 2-3 volts of ringing at the mosfet gate, at a frequency of about 4 times the actual drive frequency. I've tried almost everything i can think of to fix this, i've tried incresing the number of turns, decreasing the turns, adding and removing coupling capacitence, but i cant really improve it. Adding more capacitence helps a little bit up to a point, but its still not too good. The effect varies with voltage as well, with a 2 volt signal, the wave form is fairly clean, except for some little notches on the rising edge, at 4 volts its actually quite good except for about 1 volt of over shoot, but at 10- 12 volts, there is about 2 volts of overshoot, then some ringing, and it finally levels off to about 8 volts, so whats happening?
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
Are your primary/secondary wires in a twisted pair? At several 100khz just the smallest amount of inductance can cause possible ringing like that. As far as the overshoot you can try playing with the gate resistor as it may eliminate that.
Registered Member #1617
Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139
WOW Thanks! you wouldnt believe how well that worked! I added a 2.2 ohm resistor in series with with the primary of the transformer and all the ringing is gone now! but still some overshoot/'droop' but thats most of the problem gone! thanks!
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Gate drive ringing
