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Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
ARGH I built HV labs plasma speaker and the actual circuit works great, I tested it with a speaker, but when I hook up the fets and try to get an arc I think they immediately blow? because the Source wire gets extremely hot. I have gone through 5 fets trying to figure it out :( I have tried using a socket first - I got an arc for about 5 seconds and then the arc went away and a few seconds later the source wire disintegrated. Then i tried mounting the fet on prototype board and then point to point solder. Both with 16 swg wire and each time there would be a spark at the fet side when it started up and then the source wire would get hot. What's happening?! I can't scope it because it dies to fast. I have been troubleshooting for the last few hours so any help would be appreciated
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Ok I am only running one, not both, so I can figure out what's wrong easier. And I think I figured out the problem... I went with a 400v fet instead of the 100 and it worked then died almost immediately but i noticed that it heated up incredibly fast so I think it just heated up faster than the sink can cool it down. Which is really not good because the sink is fan cooled...
EDIT: It overheats in less than a second so I have no idea what's wrong
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
that circuit needs either an rc snubber or zener clamp on each fet. If the gate signals are not overlapping the energy in the leakage inductance will avalanche one of the fets. it will be worse with just one fet, as then what you have is an unclamped flyback! if the gates signals are overlapping then the fets will be momentarily shorting the supply on each cycle.
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Ok what's an rc snubber haha? Oh and I accidently found this, (4th post and down) which is the same problem I am having. So maybe I will try replacing the BC549 transistors?
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Sorry for the double post but I have some updates. I took out both BC549 transistors and replaced one of them, then I replaced one FET and then it ran! however, when I was messing around with it, I turned up the current too much or something and my source wire glowed... here are the remains
Thanks for all the help but I believe I got it from here. 2Spoons, can you elaborate on the snubber?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The RC snubber is not your problem, the poor design of the circuit is. -Replace the discrete gate driver with gate driver ICs, put 10 ohm resistors in series with the gates. OR use a better discrete circuit, I can elaborate on this if you want. -Make ultra short connections with thick wires everywhere !!! -Wind the primary with the halves over each other to increase coupling -Use 100V FETs with low Rds-on, under 30-40 mOhm.
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
-if you could elaborate that would be great! -I made them shorter but I can't do too much until I get a smaller battery and build a box -done (thanks) -Right now I have 400v free samples that are working quite well. No overheating and i can have the duty cycle at 100 percent without anything heating or blowing up. I replaced the source wire with 12swg battery cable.
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