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Steve's Mini SSTC, again.

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Munkey

Wed Sept 26 2007, 06:35PM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

I suppose you are thinking not another topic on this!

So after failing to design my own SSTC, I though I would make the very popular Steve's mini SSTC I have seen people make that successfully, but I have questions...

Even before I have even made it I have blown up 4 of my 5 UCC chips just by "testing" them. And I am saving the last one for the actual one when I get enough money to by the diodes and FETs (of "...") Anyway, I wondered if I could make the UCC chip drive some BD139 and BD140 in a full bridge (I will post schematic later) to hopefully make them last more than a few seconds in my hands! Will that work?

And would it work with a 1uF tank cap? Would I have to change the primary windings?

My secondary is long and skinny, it has just over 1300 windings over a 2inch cardboard former, will I have to change the primary/tank cap to make it work?

Thanks!

Zum Beispiel

Wed Sept 26 2007, 06:43PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

A quick search on datasheetarchive.com tells me that BD140 and 139 are PNP and NPN transistors... These will need a completely different driver than the regular UCC+GDT combo.

You need N-channel mosfets for this job (the GDT gives isolated drive to the upper fet(s)).

And what tank cap? It's a regular non-resonant primary SSTC, so there is no tank cap.
Do you mean the DC blocking cap on GDT primary? or the caps accross the bridge supply rails?
In either case 1ÂµF should be fine.

Munkey

Wed Sept 26 2007, 07:29PM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

Zb wrote ...

A quick search on datasheetarchive.com tells me that BD140 and 139 are PNP and NPN transistors... These will need a completely different driver than the regular UCC+GDT combo.

All the UCCs do Is make a full-bridge, right? So I am extending the current capability by making it drive bigger transistors and making it more robust, hopefully making it harder to kill. I think... Heres the schematic:

Zb wrote ...

You need N-channel mosfets for this job (the GDT gives isolated drive to the upper fet(s)).

I'm confused...

Zb wrote ...

And what tank cap? It's a regular non-resonant primary SSTC, so there is no tank cap.
Do you mean the DC blocking cap on GDT primary? or the caps across the bridge supply rails?
In either case 1ÂµF should be fine.

I think it is called a tank cap, its the 0.68uF ones on this schematic:

And the different secondary shouldn't really matter...

Zum Beispiel

Wed Sept 26 2007, 07:56PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

Oh, sorry. I though you meant to use the BD140s and 139s in your bridge, my bad.

Yeah, I guess you can use transistors to boost the UCCs output power, but I think it is easier just to parallel a few drivers if you need more power. Atleast I imagine this would be more trouble free.

Do you know what killed your UCCs? I've found them to be pretty hard to kill. Do they heat up? Try adding more turns to your GDT and using a different size DC-blocking cap. Also, these things need a lot of decoupling. I used a 100nF poly, 10ÂµF tant and a 470ÂµF electrolytic on my UCCs in my bigger SSTC.

Oh, and the secondary size won't matter. The driver is self tuning, after all.

Munkey

Wed Sept 26 2007, 08:09PM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

Zb wrote ...

Oh, sorry. I though you meant to use the BD140s and 139s in your bridge, my bad.

Yeah, I guess you can use transistors to boost the UCCs output power, but I think it is easier just to parallel a few drivers if you need more power. Atleast I imagine this would be more trouble free.

If I could get them for cheap I would

Zb wrote ...

Do you know what killed your UCCs? I've found them to be pretty hard to kill. Do they heat up? Try adding more turns to your GDT and using a different size DC-blocking cap.

Ok I am going to keep it short. I over-volted them all when they were in the breadborad stage. I made the driver (but without the GDT and half-bridge because I didn't and still don't have the parts) to drive a FET for a flyback driver, and each time for some stupid reason I managed to turn the voltage control knob on my PSU right up frying them. FOUR TIMES IN A ROW. I am the walking curse

Would the primary size matter?

Ken M.

Wed Sept 26 2007, 09:29PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Just use 10 turns.

Steve Conner

Thu Sept 27 2007, 09:06AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

UCCs have plenty of power, they shouldn't need boosted. If you're killing them, you're just doing something wrong, and you need to figure out what and fix it, instead of adding bits to the circuit.

Munkey

Thu Sept 27 2007, 02:59PM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

^ I when I killed them I wasn't using them in the SSTC schematic. I was just fiddling with them on the breadboard making them drive fets for a flyback. For some stupid reason I would over-volt them, like my hand slipped and hit the voltage control knob on my PSU thats powering it, that happened three times. Or I connect the breadboard up when the voltage is set to full (twice) of coarse blowing them. Or putting a voltage regulator in backwards and feeding it 40V Fireworks! Fun, Fun, Fun. NOT.

And I just blew up my last one when trying to make this:

circuit. powered it on 24V... nothing (there was an output though), powered it on 32V CRACK! the top of my last UCC chip blew open. im F***ing pissed of now. I try, I fail, why bother trying?

I can't beleve a little SO-8 SMD chip can provide so much power, they don't even have a little heat-spreader on the bottom...

Steve Conner

Fri Sept 28 2007, 08:53AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I guess you hadn't RTFDS and you didn't know that the maximum supply voltage UCC's are rated for is 15V?

Dr. H.

Fri Sept 28 2007, 11:11AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

If you look closely to the circuit you will see that the UCC is feeded with 12v instead of the full voltage.

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