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Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
2 is better than 1, 3 is a no no. Go back to 1 and 2, zoom out so you can see the pulse. Can you see any gradual or rapid rise in amplitude on either of the channels? Specifically at the beginning or end of the pulse..
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
hrm On mine I am seeing a rise in voltage which seems to want to reverse through the tantalum cap. It is overheating and changing color lol. I will try swapping out with a bipolar to see if it makes a difference, although I hope the reverse voltage doesnt blow my UCC's. In the meantime I am uploading a video of some test I took to show everything. It will take a while to upload so I will post it when I can.
Your GDT pulse looks just fine though. Which tells us that the circuit is working as it should. I dont mean to echo what has been said throughout this thread, but our problem must be with the way we designed our boards.. causing voltage spikes, parasitic inductance, etc.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
That's certainly what it is looking like. Would not have thought it could have that big an effect. I am waiting for the EVR board and another container load of UCCs to arrive before I continue testing. Look forward to seeing the video.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Click here for full exposed noob (troubleshoot vid)
Right now I'm redesigning the board layout...sigh
Let me know what your thoughts are. Re. The gdt waveforms at the end, The excessively long leads on the primaries and secondaries definitely is causing major leakage inductance. I had forgotten about that for the testing, as well as keeping the cores close to the bridge and drivers. But i do no attribute that to the voltage spiking and heating of the regulator, which is still a problem.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Bushman wrote ...
The signal generator producing the 100kHz test signal is at 5v PP square wave. The modulator input is a 9v 180Hz signal. The gate driver output is +/- 15v . The GDT is a 10:20:20 turn coil. so the 2:1 increase pushes the secondary output to over 30v. Initially I had a 20:20:20 GDT which was causing the same heating problems (don't recall the secondary voltage of that). Based on minibrute design and EVR recommendation I rewound it to a 10:20:20.
I have a large coil of unsheathed cat 5 so I can easily combine 2 or more strands to make whatever I need. For my last coil I wound a straight 13 turn GDT driving the same IGBT and the UCCs run happy as can be. I was surprised how bad the output quality was from the 10:20:20 coil I wound using a split and parallel primary. But winding a similar ratio transformer by just wrapping the primary around 10 times gave a much cleaner signal. GDT seems very critical to overall success.
The modulator input needs to be 5V, not 9V. You will damage the input logic chips with a 9V modulator input. In our legacy modulators, we use a voltage divider 750 / 1k to step the 9V signal to a 5V signal. For the miniBrute with a 1k pull-down at the input, a 750 in series with the modulator will resolve this. This is described in the miniBrute addendum PDF which is downloadable from our website.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
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.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Bushman since you have a signal out of your transformers do you think that any of the semiconductors are bad or mislabeled or mis wired on your bridge board?
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
That was my first thought too. Circuit is pretty straight forward and I have triple checked the layout. Seems good. I tested the components including the IGBTs and all seems good. Problem is the only way I can test (that I know of) is to blow a gate driver IC - so I am really gun shy now as it's getting expensive to flick a switch. It's not like I can feel it getting warm and shutdown - it dies almost instantly with no warning. If I could find another way to debug without having to power everything up and cook a $3 IC each time I could start testing different sections/components. Make sense?
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
The same ucc failures happened to me years ago when I first built Steve Wards mini sstc. I found a solution by using a pull down resistor on the interupt pin (3) of the ucc chips. My only thought was that feedback was causing the chips to "overclock" I realize they have some internal trigger buffer circuity but noise from GDT was getting in.
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Gate Driver Problem
On mine I am seeing a rise in voltage which seems to want to reverse through the tantalum cap. It is overheating and changing color lol. I will try swapping out with a bipolar to see if it makes a difference, although I hope the reverse voltage doesnt blow my UCC's. In the meantime I am uploading a video of some test I took to show everything. It will take a while to upload so I will post it when I can. 
