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Gate Driver Problem

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LAN_403

HV Enthusiast

Wed Jan 23 2013, 02:09PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Bushman - I will send you a FREE minibrute board kit. Just send me an email again with your address so i have it at the top of my inbox. This will include a half-bridge board as well and i'll throw in two (2) IGBTs too!!!!

Graham Armitage

Wed Jan 23 2013, 02:33PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Terravolt - I like the idea of the resistor to temporarily protect the driver IC. Will give that a try as I am on my last chip (more on the way). I have checked for shorts and soldering and everything looks ok there. I wound a new GDT last night with a 10:20:20 config with a split primary and the output signal was horrible. I cannot hear it singing (with secondaries open). Given the bad wave form, I did not want to drive the GDT with it performing like that. I have checked the phasing of the output and that is good. The wave form of the original GDT actually looked good at the gate of the IGBT until the driver fried.

I am going to redo the H-Bridge completely and check all the components again for a bad one. If there are excessive voltage spikes because of my design there could be excessive clamping. The voltage output from the GDT is over 35v and I believe the diodes clamp at 33v. Not sure how significant that is.

teravolt

Wed Jan 23 2013, 02:34PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

wow that is a generous offer I would do it. However he has spent a lot of time on his own board and I think that the problem is minor and could be fixed with a little investigation of the area from the drivers to the gates of the mosfets. Physics Junkie found his.

Graham Armitage

Wed Jan 23 2013, 02:36PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

EasternVoltageResearch wrote ...

Bushman - I will send you a FREE minibrute board kit. Just send me an email again with your address so i have it at the top of my inbox. This will include a half-bridge board as well and i'll throw in two (2) IGBTs too!!!!

Wow - thank you so much - I did send you an email yesterday. Will PM you again. Very generous indeed. I know your board design works and at this stage would be happy to get this working. I can always play with my own board design at a later stage.

Inducktion

Wed Jan 23 2013, 04:08PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Wait a second, I thought tantalum caps are polarized...

You're using it as a DC blocking cap. I'd worry about heating up in that capacitor, because tantalums absolutely hate reverse voltage.

Personally I'd replace it with a non-polar cap, something like ceramic, maybe.

UCC IC's are also really sensitive I've come to learn... As everyone else suggested it sounds like a problem with the GDT.

Graham Armitage

Wed Jan 23 2013, 05:28PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

I used a bipolar electrolytic in my last coil and it worked just fine - I chose that out of ignorance as opposed to astute electronics knowledge

Physics Junkie

Wed Jan 23 2013, 06:01PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Bushman wrote ...

I am going to redo the H-Bridge completely and check all the components again for a bad one. If there are excessive voltage spikes because of my design there could be excessive clamping. The voltage output from the GDT is over 35v and I believe the diodes clamp at 33v. Not sure how significant that is.

What is the Vpp that you measure on your gdt secondaries? Assuming your signal generator is outputting a 5vpp square wave, your secondaries should be20vpp or less. Take a differential measurement to check this. If its more than 20vpp than you might be close to solving your problem. Also, might I suggest using cat5 cable to wind your transformer, either that or tightly twisted trifilar windings. Start with 10 turns and do some tests, adding turns if needed, i know it can be time consuming but It might help. I also use tiny colored pieces of electrical tape to mark the ends of the primaries/secondaries to make it easier to see where my connections are, for example i use green for the gates, red for return, etc..

Graham Armitage

Wed Jan 23 2013, 06:16PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

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.

Physics Junkie

Wed Jan 23 2013, 07:46PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Yes indeed. I do recall the schematic showing 10:20:20, I've personally never tried this, always done a 1:1:1 ratio with minimum of 10 turns and it seems to work well. I power the UCC's on my little sstc at 12v and GDT 1:1:1 ratio with 16 turns and it works great. Whatever works i guess

once I finish tests with my new wound cores ill post a pic of them or maybe short video for comparison

Graham Armitage

Thu Jan 24 2013, 02:13AM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

So, I did some tests with 3 GDTs. none of them have particularly good outputs. GDT1 is the first one I wound that was killing UCCs. As you can see the output is around 30v PP.

GDT 2 is a simple 13 turn 1:1:1 which gives a half decent output. I have not tested this on the H-bridge yet.

GDT 3 is the 10:20:20 wound by splitting the 20 turn primary and connecting the 2 ten turn primaries in parallel (assume this is how it's done). Waveform looks worse though.

]gate_drive_transformer_tests.pdf[/file]

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