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Registered Member #1169
Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251
Statement of the issue: I am 90% positive there is a short somewhere within the high voltage section of my minibrute tesla coil.
Symptoms: The high voltage charging lite no longer comes on when I slowly turn up the variac (i checked the fuse of course). as I slowly crank up the voltage, the variac physically starts to vibrate and hum as it would if I was pulsing streamers. This leads me to believe a lot of current is flowing through the variac. @ 30volts the wires can get extremely warm and the fuse has popped several times.
What I have tried: In the image below I have disconnected the DC+ terminal from the half bridge to see if I can charge the main capacitors which I did several times. I then reconnected the terminals but removed the IGBTs. The high voltage lite came on, the relay was working properly and the resistors bleed out the caps properly.
When I reconnected the IGBT I started getting the humming from my variac.
I was not convinced that I had blown my IGBTs so I connected the low voltage portion to see I could hear the IGBTs switching as I used my interrupter. They seemed to be switchin just fine.
Question: Is it possible to have a blown IGBT that still switches? The only reason I ask is because some of you may know the HGT1N40N60A4D is hard to find these days, so i want to make sure they are the issue before I start buying more transistors.
However it is entirely possible when I removed the IGBTs I was no longer completing the circuit.
Registered Member #154
Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260
Hi Austin, As you suspect, it sounds like your IGBT's and developed a short circuit, also check your TVS diodes. If you apply low voltage to your driver, you will still hear the interrupter switching pulses from your GDT as normal.
I'll have the same problem when i blow my bridge (and i will) HGT1N40N60A4D's are hard to get now except i beleive Farnell have some left but they are REAL expensive! Have you tried the IXYS equivelent ones? or HGT1N30N60A4D's?
Registered Member #289
Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154
Sorry dude, your IGBTs are dead.
You have effectively ruled out the TVSs and diodes by testing the entire system with only the IGBTs removed. The buzzing will be there regardless of the IGBTs state. You don't have to replace them with the same PN, look around, there are better parts out there. Try Microsemi.
Registered Member #289
Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154
Glad to hear you found some replacements, now you just need to figure out how to keep them alive
Finn Hammer wrote ...
hvguy wrote ...
Try Microsemi.
Aron: tell us everything you know!
Cheers, Finn Hammer
I don't know Finn, that could take minutes! Haha, seriously, I have tested a bunch of those APT parts and found the APT75GP120JDQ3 to be a good choice. I try and stick with 1200V parts so I have some headroom for noise, but if your pushing that current SOA, whats the point The SOT-227 parts are cool, but I prefer the bricks, they are so much more robust... That being said your new circuit may mean these slower/smaller/lower V parts could be made to work more reliably. I really can't wait to get it on the bench again...
Registered Member #1169
Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251
Got my bricks last weekend and installed them...she is now purring like a kitten. I didn't know these IGBT's could still make a switching noise after being blown...
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IGBT troubleshooting scenario
The SOT-227 parts are cool, but I prefer the bricks, they are so much more robust... That being said your new circuit may mean these slower/smaller/lower V parts could be made to work more reliably. I really can't wait to get it on the bench again...