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lpfthings

Sat Sept 19 2009, 04:28AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Hey guys, Harry recently sent me 2 "FGA15N120ANTD" IGBT's (Thanks again Harry :) )

I have a small flyback here, that I am driving with a 555 driver and a small N chan MOSFET. I can only get like 1cm sparks from it using that circuit, and it doesnt draw much current at all, so I was hoping to use these to get some much more interesting results. I have never worked with IGBT's before, and Harry recommends I use some kind of 555 circuit.

Does anyone have any idea's on a nice beefy driver I could build with these things?

Cheers,
Dan :)

Arcstarter

Sat Sept 19 2009, 04:55AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Ideally you should have something like a mosfet driver, or some kind of transistor to drive the gate of the IGBT. Use 50% duty cycle, if you can measure it somehow. If you have too low duty cycle, you won't pull much current. Also, if you have some zeners, you should put two 12 or so volt, back to back zeners from the gate to the common ground.

Other than that, i am not sure what else you'd want me to suggest.

Good luck :D

lpfthings

Sat Sept 19 2009, 06:22AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

So I can use the regular 555 driver, and just swap out the MOSFET for a IGBT driver and IGBT?

Cheers,
Dan :)

Dr. Dark Current

Sat Sept 19 2009, 07:52AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

If it was me, I'd slap that IGBT on a large heatsink, put 800V worth of transils on the C-E, wind a 30-turn primary on the flyback and supply with something like 80 volts (use a variac if you have one)...

The IGBT will probably heat a lot, but you might get some serious arcs

Drive with 555 at something like 20kHz (just connect pin 3 directly to the gate) and if using a DC flyback, make sure the primary polarity is right...

Then you might try the resonant cap mod, and of course, a half-bridge...

lpfthings

Sat Sept 19 2009, 09:12AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

hmmm .. getting 80V @ a reasonable current may be a bit difficult, the cheapest variac around here is like $200AUD, and shipping on one from ebay etc would probably cost more than the variac itself :(

Also, what do you mean by "transils" and "C-E"?

Cheers,
Dan :)

Proud Mary

Sat Sept 19 2009, 10:39AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

lpfthings wrote ...

Hey guys, Harry recently sent me 2 "FGA15N120ANTD" IGBT's (Thanks again Harry :) )

I have a small flyback here, that I am driving with a 555 driver and a small N chan MOSFET. I can only get like 1cm sparks from it using that circuit, and it doesn't draw much current at all, so I was hoping to use these to get some much more interesting results. I have never worked with IGBT's before, and Harry recommends I use some kind of 555 circuit.

Does anyone have any idea's on a nice beefy driver I could build with these things?

Cheers,
Dan :)

Hei Dan,

if I gave you the impression that you could or should drive the IGBTs directly from a 555 then I must have got out of bed the wrong way.
You must have a driver circuit, lad, as others have suggested, either a two transistor affair, or preferably a dedicated MOSFET driver chip which I know may be difficult for you to obtain. You must protect the devices against inductive kick-back spikes, unwanted over-voltages, and be sure to clamp the gate with a zener diode.

I did promise you I would send you a suitable driver circuit to go with the IGBTs, but things have got on top of me recently, and I am very sorry that I forgot.

But not too late to put it right now, is it?

Dr. Dark Current

Sat Sept 19 2009, 11:05AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

The IGBT has a gate capacitance of only 2.5nF, that's perfectly fine to drive it directly from the 555 output (which AFAIK can supply something like 500mA peaks).

C-E is collector-emitter, IGBT's are not avalanche rated and if you exceed the maximum voltage rating just for a moment (such as an unprotected flyback converter), it's dead.

Transil is transient voltage suppresor, kind of like a high voltage zener diode.

lpfthings

Sat Sept 19 2009, 11:15AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Harry wrote ...

But not too late to put it right now, is it?

Not at all, I am open to any suggestions

I think the problem is with the power supply. To get 80V or so would require rewinding my MOT, or buying a 40-0-40 toroidal transformer, but then I have to rectify and filter it, which would probably require about 82,000uF of caps to get it down to 500mv ripple.

Dr. Dark Current

Sat Sept 19 2009, 11:20AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

lpfthings wrote ...

Harry wrote ...

But not too late to put it right now, is it?

Not at all, I am open to any suggestions

Well then, you can rectify, or even double(!) your mains (240V land right?), and kill your flybacks with a half-bridge...
You'll probably need a pair of gate drivers and a GDT though, and don't forget antiparallel diodes.

EDIT: I think something like 4700uF of filtering would be more than enough (for the 80V supply).

Proud Mary

Sat Sept 19 2009, 12:12PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Dan, something like this should do the trick, and uses very inexpensive parts, though I'm sure others will want to come forward and suggest improvements

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