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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Get rid of the diode !!
Then, make sure it's not the scope which could be picking up interference. Leave the scope connected to the circuit, but short the probe to the ground clip (or to 2nd probe if you are running in differential mode). If you can still see ringing (without the square wave of course), then the scope is your problem.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
furnace wrote ...
I usally dont connect the negative rail of the scope cause it shorts the circuit but ill try running without the scope and see what happens.
And there's your problem. Without a ground reference, every measurement you've ever taken is worthless. It's like poking a single multimeter probe onto the live wire of a 240v circuit and saying "nope, no voltage here"
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
Location:
Posts: 108
I finnaly got the gate signal ok by reconnecting evrything on my 15v supply , shortning gdt wires and winding all the wires together of the gdt. The first pic is the primary and secondary side of the gdt conected to the igbt. The second pic is the negative of my igbt and the tank, as you can see there is still alot of ringing or paracitic oscillation so i think it must be my caps on the igbt which are .22uf 2000vdc. Any advise on this would be great.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Yes, probably oscillations between the .22 uF bypass caps and the main filter capacitor. Increase the capacitance and shorten the leads to te electrolytic cap(s).
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
Location:
Posts: 108
So this is what i got after adding 600v 10uf caps on my igbt. I dont know if the signal is ok like this because there still seems to be a little bit of ringing which i cant seem to get under controll and another thing that bothers me is the voltage on the igbt.Is my igbt suppose to read the exact voltage coming from the variac because when the variac is on 25v my igbt shows 100v and my tank is on 200v. Just want to know if this is normal
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Gate drive signal
