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Third SSTC - Mosfet Drivers Exploding

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SuperZanti

Mon Aug 27 2012, 01:00AM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

So, the way my drivers are blowing up, it seems like I'm getting a lot of kickback voltage on the transformer. (correct me if I'm wrong)
I'm wondering if I added the zener diodes pictured here:

, if it would prevent my drivers from blowing up. But then that brings up the question: Why am I getting so much kick back?

zzz_julian_zzz

Mon Aug 27 2012, 05:04AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

It may not related to above comments, but... did you use this schematics?

You've noticed the D6-D7? they are clamped to only 5v, meaning, the output will only be 5v, then your interrupter switching up to 12vdc.,. i don;t know if this does make sense but could be also your problem... The levels of those 2 signals, (interrupter and feedback hex schmitt) are inputted on the 2-3 pins of UCC ics, if you look at the datasheet of the UCC, they are subjected to logic gates inside the chip... maybe, if the 2 signals are identical in terms of v level, then it might work correctly.. (NOTE: you cannot make tl494 to 5vdc).....

Also, do not push to Full bridge yet, just make TC work in to half bridge to lessen your problems, you can also test the UCC into bread board if they are responding correctly with respect to Enables and input..

UCC37322 = NOT INVERTING
UCC37321 = INVERTING

if the IC works properly, next thing you check is when it is subjected to fast signals with the ENABLE pins connected to +12v via 10k resistor. Then put a 555 timer supplied from 5v oscillating on your coils resonant frequency. like this one here:

i recommend this circuit to do first..

SuperZanti

Mon Aug 27 2012, 04:08PM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

Yeah, I've already done the half bridge design and I got that working really well. That's why I don't think there is a problem with my antenna or divers, but with the bridge its self (or compatibility problems). I haven't yet manually tuned it to my coil, but I have replaced the PWM controller with a 555 timer (I can now switch between the two), so I've tested both. Maybe when i get some more money to buy parts I'll try manually calculating my resonant frequency to see if it works. However, I still believe it's got to be something wrong with the bridge.

zzz_julian_zzz

Tue Aug 28 2012, 05:11AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

what are the wires used in the GDT? replace it with a 24awg UTP wires instead. What type of GDT core used?
how many turns in pri & secondary?

If you got it working with a halfbridge, you can leave the driver circuit on its current state, the problem is on the bridge. You can re-lay out to other forms to make sure that there are no faults on it.

SuperZanti

Tue Aug 28 2012, 05:41AM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

Its a ferrite torid with 22awg magnet wire. 15 turns with 7 twists between the five wires. It's supposed to be the best configuration for the GDT. Would UTP wire work better? Also 24 AWG?

I have 1000 turns on my secondary and 5 on my primary. That's 1000 turns of the 22awg magnet wire and 5 turns of coax cable.

Unfortunately I'm kind of scrapped for cash, so I apologize, but I can't do a whole lot of testing to see what the error is. I'd like to try and figure it out before my next build.

Thank you so much for your help!

zzz_julian_zzz

Tue Aug 28 2012, 12:21PM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

I understand. yep 24 awg standard LAN cable are one of the most common winding wires for GDT application.
I am afraid that the 22awg and its 7 twists makes the UCC chip hard to drive the MOSFETS,,, make more twists as possible,. 15 turns pri-sec should do fine. please show your actual bridge schematics, and the actual photos of it, I wish to find the mistake on the possibly wrong connection on it. (please make the photo very detail - if not.. do have many pics) different view and zoom

E.TexasTesla

Tue Aug 28 2012, 04:32PM

Registered Member #4362 Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98

Is your primary winding in phase with feedback circuit?
Try reversing connections at primary winding.

Never mind. I see your schematic is drsstc due to the tank cap c2 c3.
I dont think this will ever work with secondary antenna feed back.

SuperZanti

Tue Aug 28 2012, 06:08PM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

Wow thank you so much for all you help everyone.

I've posted some pictures of my setup as well as the schematic, but I'll do them again to make sure they're all updated.
This is my schematic:

I designed a PCB for everything before the GDT and everything on there is modular so I can easily replace parts. I'm 100% sure that my PCB is the exact same as the schematic. Though since it's modular I can easily change the value of a capacitor, or diode, or whatever.

As far as making a new GDT goes, I will definitely need a bigger ferrite core. Does anyone know where I can scrap one really easily? Also, is it standard CAT5 cable that you're talking about?

Is that really 24awg? I work with that cable a lot and to me it feels much thicker. Maybe 18 or 20 awg.

Also, I apologize because right now I only have a camera phone to work with. I left my other camera up on a mountain during a recent camping trip. So I'll do the best I can with the pictures.
Here is just the secondary coil:

Here is just the primary coil: (I have a ton of extra coax cable so it's easy to make more)

Here are both of them together:

And here it is with the topload: (note, I have not tested the coil with the topload yet, since this topload was made for my SGTC I'm afraid that it is too big for this SSTC)

Here is my driver board: (everything right up to before the GDT)

And finally, what you were really asking for, a million pictures of the bridge: (I know the wires are too small for the voltage, but I haven't yet gone past 50v DC and things are still blowing up)

Also, regarding the last post, there are lots of well known schematics that are very similar to mine.
For example Kaizer SSTC II
Steve's SSTC 5
and Steve's SSTC2

zzz_julian_zzz

Wed Aug 29 2012, 10:49AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Hi my friend,

First things first.. on your schematics, you used 12vdc on your 555 timer, you might want that to lower on to 9v and put 500ohms on its output or before in the pin3 UCC. You can also, replace those C5/C6 to ceramic .1uf and then parallel those each to 10uf ceramics. C4 can be replaced to 1uf or 2uf ceramic. I am very confused on your GDT schematic. D1-D4 can be removed to minimize the error and complexity of the bridge. Important: ADD SNUBBING CAPACITOR. put these as close as possible to each pair of mosfets (per halfbridge) you can put 10uf/200vdc on each pair connected to +120vdc and -120vdc.

Next, utp cables are commonly 24awg thicked, the thing in the picture is correct.

Secondary coil is good, but remove those aluminum tapes on its top and bottom.

primary coil is bad, higher current on the bridge will flow on the pri coil, so its not a good idea to use such thin wires, (the conductor inside it) and just thick insulation, you can use 14awg atleast 6 turns.

You are correct, the topload is too much!, you can leave your coil without it. trust me, it will perform better.

Driver looks very defined. Thumbs up for that.

I am sorry, but I am completely confused on your bridge lay out. then, avoid using that plyboard as a PCB, its a bad thing to use such material on a high Fres circuit like SSTC.

I post some of my bridge to give you an idea (just don't mind the CT, on the middle, look at the arrangement of the MOSFETS, and thicker wires used on it.

SuperZanti

Wed Aug 29 2012, 02:41PM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

First, I'm kind of stubborn to change anything on the driver circuit. Except maybe the type of capacitor. This is mostly because of this schematic:

Which seemed to work very well for Kaizer.

The GDT in my schematic is just something I made real fast because altium designer didn't have a 1:4 transformer schematic already there for me to use.

It was also recommended to me to use IRFP260's since I'm only running on 120V AC. Should I do this?
I'm not quite sure how to do snubbing capacitors, I've heard of them but I'm not quite sure how to implement them.
I'll definitely change the GDT and the Primary coil. (btw, how are you confused with my GDT and bridge? also, with yours it doesn't look like you used cat5 cable)
I also noticed that on everyone's sstc's they have huge tank capacitors, not just the small film ones that I do. Should I change this? Edit: these are the snubbing capacitors, am I wrong?
Finally I noticed that your resistors look like they're rated for very low power. I'm using 15W resistors because my other ones kept blowing up on my half bridge (and when I got the full bridge working once).

Thank you so much for your help, I'll look more into it when I get back from work.

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