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Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Bushman, I believe now that the problem is in fact the DC blocking tantalum caps. I just tried some 10uF multilayer ceramics, I would have done film caps but I didnt have any. Anyways the problems are now gone! No more weird regulator shorting no more rapid heating of the ceramic cap or regulator. The circuit now works fine with the modulator no matter if the bridge is connected or not. Only problems to fix now is the leakage inductance on the GDT and some really weird "sine wave like" ripple on the output of the driver in correlation to the pulse width from the modulator. I hope this helps!
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I tried some of the testing suggestions and made progress. I added a 4.7ohm resistor in series with the 1uF DC blocking cap. With the IGBTs installed I was able to run the modulator without any problems. So I tried a 1ohm resistor and it still worked. Then I read Physics Junkies success and switched to a 10uF bipolar. Everything ran fine with no heating for several seconds. Then one of the UCCs went POP with lots of smoke.
What was interesting was that it ran for a while without any heating, then within a second it went from cold to fried. That makes me think it's not a simple load issue. Wonder if something on the driver board is causing it go into constant-enabled mode. I am watching the 100kHz signal on the scope and not the 180Hz, so I would not see if that happened. Could that be possible?
I have checked all soldering and components. A photo of upper and lower part of the board is shown above.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
EVR - Just picked up the mail and received the board and components you sent. Thank you very much - that is really kind of you. It is much appreciated. I think this is going to help me with my problem. Now to start assembly again and hopefully get this resolved.
Registered Member #5258
Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119
Bushman wrote ...
I tried some of the testing suggestions and made progress. I added a 4.7ohm resistor in series with the 1uF DC blocking cap. With the IGBTs installed I was able to run the modulator without any problems. So I tried a 1ohm resistor and it still worked. Then I read Physics Junkies success and switched to a 10uF bipolar. Everything ran fine with no heating for several seconds. Then one of the UCCs went POP with lots of smoke.
What was interesting was that it ran for a while without any heating, then within a second it went from cold to fried. That makes me think it's not a simple load issue. Wonder if something on the driver board is causing it go into constant-enabled mode. I am watching the 100kHz signal on the scope and not the 180Hz, so I would not see if that happened. Could that be possible?
I have checked all soldering and components. A photo of upper and lower part of the board is shown above.
What you are describing sounds like a latchup scenario in the drivers. There are a number of things that can cause it so I wont' speculate but that is most likely what is happening. You could test for this by putting a 5W 100 ohm resistor in front of VCC for each of the drivers. When the condition arises that causes the latchup happens you should see a maximum of 150mA draw from each of the drivers while dissipating 2.25W across the resistors (assuming 15V power input). This will not be enough to blow the drivers but will be enough to hold the drivers in the latchedup state. I had the exact issue with the same drivers in another circuit. Doing this allowed me to find the errors in the design that were allowing the latchup to happen in the first place. Of course if you are switching to the EVR board this is probably a non-issue now, unless your still curious.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...
Glad you got it working. I did mail you a miniBrute board set and some IGBTs.
Can you provide some information on the type of tantalum capacitor you were using? I'd be curious to know. Part number?
;
Tantalum capacitor with part number. The only Difference between these and the ones in your design book (that I could tell) is the +- 20% tolerance vs. +-10%.
Heres the capacitor I switched to, its all I had available
"I did mail you a miniBrute board set and some IGBTs"you sent me a board set as well?? or was that comment to bushman?
----------- Here's my issue now. Below is a pic of the Interrupter at the output of the Inverting Driver WITHOUT the GDT connected, Everything looks fine, you can even sort of see the delay which is good too. Yellow trace is directly form the interrupter, Blue is on the output of the driver after the 10uF ceramic capacitor.
Now with the GDT and bridge connected. NOTE: this is nothing new with the ceramic capacitor now in place, I was also getting this when the tantalum caps were there.
Decreasing the PW down to lowest setting (roughly 10us here) causes the blue trace to flatten, shown below. Increasing the PW will Increase the amplitude of the blue trace.
EDIT: Am I just seeing a start up pulse (to get primary oscillations going) through the core here? The reason I believe its a problem is because when the primary feedback signal is in place, it will follow that sine-like wave path, resulting in a synchronized waveform that's all sorts of messed up. Is this normal or not?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Yes, i meant Bushman - sorry.
Your middle waveform looks really funky. I've never seen that before. I think you have something else going on somewhere. Maybe something really simply like a solder short or incorrect connection - i don't know. And probably because of this is why the 10uF tantalum isn't working out for you.
If you have my DRSSTC 1st Edition book it has scope shots and gate waveforms of the IGBTs using this gate drive circuit. They are very clean.
In the working world, if we ever got to this point, we would simply try building a 2nd circuit and see if we can repeat the failure. If the results are the same, than it kind of points to layout, if the results are different, then it could be circuit error somewhere.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...
Yes, i meant Bushman - sorry.
Your middle waveform looks really funky. I've never seen that before. I think you have something else going on somewhere. Maybe something really simply like a solder short or incorrect connection - i don't know. And probably because of this is why the 10uF tantalum isn't working out for you.
If you have my DRSSTC 1st Edition book it has scope shots and gate waveforms of the IGBTs using this gate drive circuit. They are very clean.
In the working world, if we ever got to this point, we would simply try building a 2nd circuit and see if we can repeat the failure. If the results are the same, than it kind of points to layout, if the results are different, then it could be circuit error somewhere.
I was getting ready to call you Santa Clause lol... (wishful thinking)
I actually am going to build a second circuit with a different layout, better layout in my opinion. Just going to take a while as some stuff from digikey got back ordered till end of February-early March. In the mean time ill just have to go back over my layout and check soldering and whatnot. Thanks
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
SUCCESS !!. Thanks to EVR I switched all components from my driver board to his and I can now run the H-Bridge without blowing anything up. Obviously something was wrong on my board design, as I used all the same components. This is the signal at the gates of the IGBTs - looks good to me. Nice sharp rise and fall times without the ringing I had before.
Thanks again for all the help. Now to continue with the assembly
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Gate Driver Problem
