troubleshooting universal driver 2.7c

[scott]

Hello everyone.
Ive been lurking for years but now its time to see if i can get some help with a ud2.7c board. I originally purchased 1 populated and 2 unpopulated boards from Gao (loanocean) built a coil (110mm x600mm secondary(120khz fres), full bridge of fga60n65(250a limit), 5kva variac) and had some success with sparks of about 18" running at 180-200v bus. Then I wanted to tune phase lead so I set it up with a dummy load (pizza tray) and cranked it up a little, all was good. I could turn up the voltage to 250v, ocd would have kicked in by now with secondary in place. Pizza  tray was hot. I stopped test so i could set up the scope but when turned it on again it didnt work. At first i thought id blown the bridge but after testing, the output from the driver was bad. It doesn't seem to oscillate anymore. The output from pin 7 of the tl3116 when a feedback signal is generated by the sig gen(100khz 5v) is just one square wave pulse. have i killed the comparator ? if so how ?
any ideas
Now before anybody replies i feel it fair to mention that my electronics kung foo is not strong.
Any help/advice would be great.
thanks in advance.
ps if anybody wants more info please ask. im working on photos please be patient this is my first post on any forum.
scott.

[davekni]

Since you are getting one pulse from TL3116 output, it's likely still fine.  My guess would be that the single pulse isn't creating enough current feedback signal to continue oscillations.

One possibility is that the initial H-Bridge output voltage is already close to the level that the one initial pulse will drive it.  Mads' solution is to add a power resistor across the H-Bridge output so that it always starts at 0V.  If you know (ie measure with your scope) which polarity the H-Bridge output is driven by that initial pulse, then you can get twice the initial kick by using resistors to pull the H-Bridge output to the opposite polarity.  One resistor from one H-Bridge output to VBus- and another from the other output to VBus+.

The pizza-pan load may be lowering primary resonant Q, so making startup require more of a kick.

[Mads Barnkob]

Hi Scott and welcome to HVF! I am happy that you decided to finally sign up and post. Be sure that we are here to help you all the way.

Here is a little help on posting in-line pictures on this forum: https://highvoltageforum.net/index.php?topic=31.msg696#msg696

While the inverter output resistors have solved some stability issues for me, I have not run into not wanting to oscillate. So I am thinking that feedback signal might not be strong enough. How is your current transformer made? material? ratio? burden resistor?

We love pictures, links, documents, schematics and videos, give us all the information you can and we can get you on the right track faster

[scott]

Thanks davekni and hello.
I have tested the driver on the bench without the inverter and with simulated feedback. still no good. The length of the pulse (3116 pin 7) changes when the interupter on time is adjusted.
if the picture works blue trace is feedback yellow trace is output of pin 7 (3116).
cheers.
scott.
edit........ i cant show scope traces. wrong format. I hate computers.

[davekni]

If you can view them on your screen, do a screen capture and post as .jpg.  That works.

Sounds like the issue may be after the TL3116, somewhere from there to GDT.  Perhaps scope GDT inputs too once posting is figured out.  (I had trouble figuring out how to post images initially too.  Many of mine are screen-grabs of TLSpice schematics etc.)

[scott]

hi mads. thanks for reply. love your youtube channel by the way.
Yes ill have a look. im finding this posting busness quite taxing.

this setup was all working fine. The inverter is also loanoceans and uses triad magnetics CST206-1a for feedback and ocd. currently using 5.1r burden resistor however i now use a 625:1 ct for my ocd made using 25x25 cascaded epcos n30 23mm ferrite cores because im not sure how to work out what voltage to set my ocd using the triad magnetics ct`s.
I cant work out what happened to it. next post should have something nice to look at.
cheers.
scott.

[scott]

Hi everyone. After some head scratching and swearing here are some pics.........
and link to video of coil test before i broke it maybe..........

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scope shot1, blue trace is feedback and yellow trace is pin 7 (3116)
scope shot2, blue trace is feedback and yellow is gate drive output

hope that helps.
scott.

[davekni]

It's hard to imagine any failure that would produce the posted square pulse on a TL3116 output.  Are you sure you are probing the correct chip?  Is the plot of pin 7 (non-inverted output) or pin 8 (inverted output)?  Can you probe the TL3116 inputs?  That is likely easiest on the diodes or resistors, say cathode of D1 or anode of D2 for the - input and the junction between R5 and R6 for the positive input.  (For probing TL3116 pin 7, the right side of R7 or C33 might be easier, where "right" refers to the schematic symbol.)

[scott]

I found it. r2(1k) was bad. It was measuring on board at 50k. replaced that and all seems ok. No idea why that happened. Must have been a bad resistor out of the packet.
davekni yes you are right I jotted down the ic`s on a bit of paper and had labeled them backwards ic8 3116 and ic7 311. what a dufus. I am more than a little embarrassed and im sorry to have wasted everyone's time.
Next is to have a good read up on phase lead tuning, read the posting guide again to try and make my posts look better and try to  get the scope to work with my laptop.
Thanks everyone.
See you in my next post.
Scott.

[davekni]

I (and everyone else) make mistakes too.  Don't worry about that.

Concerning R2 being bad, I suggest checking solder joints on L1, R1, and the phase-lead switch SV1.  If there is an intermittent open on any of those three, excess current flows to R2, enough to likely fry it.  Also, if SV1 isn't switched all the way to one side or the other, it might be open on both terminals, causing the same issue.

[scott]

Hi, thanks David. I`ll have a look at that. I didn`t think that (R1) would be a concern in my first wave of testing. It just shows to test logically rather than by assumption.
cheers.
scott.