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Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
replace the 10uf capacitor with a 100 to 200 ohm resistor temporarily so you can measure on the other side when you fire it up if it wont get to hot put your finger on it and shut it off quick if it gets warm. Hopefully the outputs of the transformers don't exceed the clamp voltages at the gates. Maby Eastern is right and the load is to great. try removing one drive at a time and see what happens.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
Terravolt - Great suggestion - would feel much more comfortable testing like that. Thank you.
I found a solution by using a pull down resistor on the interupt pin (3) of the ucc chips.
E.Texas - what size pull down resistor did you use? is that just a band-aid and not addressing a real problem on the bridge circuit? I have never seen a pull down resistor there in any circuit design. Could be useful for testing I guess to protect the IC. Thanks
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Bushman wrote ...
thanks for the video - looks like a great setup (nice signal generator). Your duty cycle is actually 1% which is nice and low - when you increase it what is the pulse width increasing to? Definitely looks like something on the driver board is overloading/shorting to overheat that regulator. Have you scoped any of the IC pins where you are processing feedback or modulation signals and see if anything weird happens there when connecting the GDT vs unconnected. The thought being to try and isolate some part of the driver board that could be causing the short.
Thanks EVR for the 9v modulator tip - will make that adjustment too as I am also running 9v.
When I troubleshoot my whole board I start with taking all the IC's out of the sockets, and trace the signals in, installing the IC's respectively as I go, following the signals all the way to the driver inputs. Although I've only done this with the GDT unconnected, I will go back and do this with it Connected, and try to see when, where, and with what IC does the regulator begin to heat. Now that i think of it, I also had this same problem with Steves UD 1.3 except the components were smd so the results were much worse. I can remember the 10uf bipolar ceramic capacitor exploding. Which only leaves more evidence yet again of a poorly designed layout..
This is nothing new, but I found this article to have some helpful tips for gate transformer design and how to properly terminated the secondaries, as well as suggested DC blocking capacitors to ensure the core does not see DC and saturate.
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
Bushman, I currently have a 1k resistor pulling the interrupt signal to ground. My interrupt signal is from a fiber optic receiver. It has been working like that for several years.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Another thing would be to remove the fets from the bridge board and see what type of signals you get at the gates. the circuitry beween the transformer and the gates. there should not be any clamping from the diodes so that energy goes into the fets and not heating your IC. Another option for testing is to replace your tanalum with a 1uf mono ceramic. this may have a high enough XC, impedance, to prevent your IC's from drawing lots of current
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I guess the 1k pull down can't hurt anything. I re-read the RichieBurnett article on GDTs which is always good refresh. I did some experimenting and switched out the tantalum cap for a 1uF bi-polar electrolytic (worked well in my last coil too). reduced the modulator to 5v and wound a 1:1:1 GDT with 15 turns. Getting a really nice 15v PP square wave output on the secondaries now without any spikes. Waiting for the components to arrive before hooking up the bridge again. I may try removing the IGBTs and test like that first - what's one more dead UCC
Thanks eveyone for all the great suggestions - this is a great learning exercise.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
When UCC's change state they are in a linear state and dissipate heat, as frequency increases so does the heat dissipation and less effective as a driver. To mitigate this you could reduce the interrupter on time to 100us at some point the frequency will not allow you to drive much of a load so if you have a tesla with a 60khz coil vs. A 350 khz tesla a resonance of 350 might not be possible with out using UCC's that come in a TO-220 package or a different scheme all together. I had problems like this in some earlier experiments. I use plastic fiber optics and direct drive for big igbts with individual supplies. Transformers work well if they are set up properly.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
I am finishing up on redesigning my board layout. Just to clarify, to reduce parasitic inductance, use thick traces and place them tightly together, keep power rails away from signal traces, and for traces that must be small or squeezed through IC pins keep them relatively close together too.. sound okay? Anything else important let me know.
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
Good tips on board layout physics junkie, I avoid runing traces between ic pins by using 0 ohm resistors when possible. They look alot better than jumper wires and they are around .02 cents each from digikey.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
E.TexasTesla wrote ...
Good tips on board layout physics junkie, I avoid runing traces between ic pins by using 0 ohm resistors when possible. They look alot better than jumper wires and they are around .02 cents each from digikey.
I'll keep that in mind, thanks. It will just be a little challenging to completely avoid traces under IC's since there are quite a few to fit on a 100cm x 80cm board.
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Gate Driver Problem
