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GDT problem on my SSTC

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vasil

Sat Mar 11 2006, 08:22PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

If you try it at low voltage (20 VDC input) input the FETs would not blow.
I never used a scope, so someone else has to answer at this question.
Just use a resistive load for your halfbridge (a light bulb) first. If the phasing is wrong, then both FETs are ON in the same time, so your setup will draw current from the mains, but the bulb would not light, because the FETs just short the rails.

EEYORE

Sat Mar 11 2006, 09:40PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

You really ought to learn about whats going on with the GDT, it will make things alot easier. Ive gotten by with just one chnll on my scope by using my interruptor. Ive never tried it with a PLL. What topology is your circuit?I was using a 74HC14 circuit. I would look a the waveforms and notice a spike on the crests of the waves and this crests position would change based on the phasing.

Matt

ped

Sat Mar 11 2006, 11:14PM

Registered Member #305 Joined: Sat Mar 11 2006, 04:27PM
Location: Liverpool, UK
Posts: 29

i know, and i will learn about the GDT's ....just need some help on this one

CT2

Sat Mar 11 2006, 11:22PM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Ok to hook up the GDT this is what I find is the best way to do it.

First you need to label your MOSFET's 1 and 2, it doesnt matter which is which, then take your wire. You'll have 3 wires; one is for the primary, and then there are 2 secondaries. You twist those toghether and then wind them on the ferrite toroid. Now once your done winding you have 6 wires ends lookin at you; 2 reds 2 blues and 2 blacks. Seperate them so that none of the colours are with them, what i mean is so that it goes 1 red 1 blue and 1 black together, and make sure that those 3 are all on the same end of the windings.

Now one is your primary so put that aside, now label your first wire, one end will be G1 which goes to the Gate of MOSFET 1, the other end of that wire is S1 which goes to the Source of MOSFET 1.The other wire is gonna be labeld the same way except beside G1 it will be S2, and beside S1 it will be G2. Then connect G2 to Gate MOSFET 2, and S2 to the Source of MOSFET 2.

That may have been a little confusing I appologize, but if you look at the diagram its pretty
easy to get it.

Gdt1qs

[Edit: Fixed oversized picture]

ragnar

Sat Mar 11 2006, 11:27PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Just looked at photos - it's a 74HC14 driver.

Your gate-driver transformer is used to couple the signal outputs from the driver to the MOSFET 'gates' ('inputs') on the bridge.

Thankfully for you it's only a halfbridge, which simplifies things a bit.

I see you've made three windings with brown, brown-white, and orange-white wire.

Where you've got three of them exiting from the "top" of the ferrite, consider these "SIDE A" of the winding. Where you've got three wires exiting from the "bottom" of the ferrite, consider these "SIDE B" of the windings.

Grab a thick black marker and mark side A on each winding, up at the wire! Now you can think of each winding as having a "SIDE-A or SIDE-B", and you have three windings total.

The critical bit is the two MOSFETs... you'll have mosfet (1) and mosfet (2). Each winding of the gate-driver tranformer is connected between the FIRST and THIRD pins of the MOSFET, or the GATE and SOURCE.

So one mosfet (1), connect SIDE A to the GATE and side-b to the source. Use the orange-white-striped wire.
then on mosfet (2), connect SIDE B to the GATE and side-a to the source. Use the brown-white-striped wire.

Now you can connect the third winding (BROWN WIRE) as the 'primary' of this gate-driver transformer to the output of your driver circuit. It's polarity isn't critical, as in, so long as your MOSFETs are out-of-phase (as described in the above paragraph), nothing will blow up. If you connect the primary winding backwards, however, the 74hc14 feedback won't work, and not much will happen. In that case you may need to reverse the BROWN primary windings of the GDT, OR you might need to reverse the windings of your primary coil on the big resonator.

Makes sense?

Good luck.

ped

Sun Mar 12 2006, 08:50AM

Registered Member #305 Joined: Sat Mar 11 2006, 04:27PM
Location: Liverpool, UK
Posts: 29

thanks for your time guys, this is my first SSTC, i'm used to SG teslas which i can build with ease

I'll hook it up later and see what happens and let you know.
And ive made a donation to the forum by way of a thanks, i have a feeling im going to be around here quite a lot

...
right people, all checked and ready to power up...but before i do...what would you reccomend for the primary? it sounds like you lot have seen this type of circuit before...

[Edit: Fixed double post]

CT2

Tue Mar 14 2006, 12:37AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

For the primary you need anywhere from 6-20 turns of wire. You dont need to use copper pipe like in SGTC or DRSSTC, just some 14-16 AWG wire should be good, thats what I'm using anyways. You CAN wind it directly over the secondary but there could be insulation problems, so something inbetween the two would help, I just have air between mine and some plastic from a 2 litre bottle of pop that fits perfectly over the secondary.

Mine looks pretty crappy right now haha but it's just for testing and it does fine.

williamn

Tue Mar 14 2006, 02:03AM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

Hey that circuit board looks familiar! I am teaching a class here at the local junior college, and decided a SSTC would be a nice semester long project for the students. I sold off all of my extra parts and boards on ebay as SSTC kits. Yes, it is a version of the popular 74HC14 self resonant driver . Welcome to the forum ped! You can wind the primary (try 16-22AWG stranded wire) directly on the secondary form (first wrap some sort of insulator like PE), or use a larger diameter form to wrap it around. I always like to use 5 or 6 turns, then tweak winding spacing and turn count until optimal. Good luck, I hope you get it running, most of my students have.
Will

ped

Tue Mar 14 2006, 07:08AM

Registered Member #305 Joined: Sat Mar 11 2006, 04:27PM
Location: Liverpool, UK
Posts: 29

thanks guys, i notice your primary winding doesn go up the seconday..its just bundled at the base? does that make a difference?

Desmogod

Tue Mar 14 2006, 07:11AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

I have noticed no real difference in performance at all.
Although I reckon the neater _everything_ is, the less chance there is something to break/not function.

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