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High-Power MOSFET/555 Driver!

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EE2K11

Mon Feb 18 2008, 04:40AM

Registered Member #1218 Joined: Tue Jan 08 2008, 02:13AM
Location: College Station, TX
Posts: 9

Check out my latest creation. It's your basic 555/MOSFET FB driver using a STW18NB40 FET and a 7812 regulator for the 555. It puts out so much power its unreal; almost ZVS-level. I bought these FETS for only 99Â¢ a pop at goldmine-elec.com , I'd highly recommend them. Input voltage is 30.1 V @ ~4 A. Flyback output is around 30 kV @ â‰¥ 3 mA. The arcs are so hot I accidentally melted a small screwdriver I was arcing with. Check it out and tell me what you think:

...

Mon Feb 18 2008, 04:47AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

that is quite impressive for a single fet!

On another note, I wouldn't recommend powering flyback off a nice supply like that, at least without a reverse protection diode and a nice big filter cap to prevent spikes from getting back in and blowing up your supply (don't ask....).

I usually use gell cells or just a variac+bridge rectifier+big filter cap if I need more precise control.

cheers

Arcstarter

Mon Feb 18 2008, 05:46PM

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

Incredible!I get very small sparks and little current even if i am using a huge battery.i try using one of my many transformers but i need a proper size filter cap.I a going to get a few of those!

Spedy

Mon Feb 18 2008, 05:54PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

WOW! what circuit, exactly, are you using? I have a flyback almost identical to that one, but no fancy power supply...

Great job, those arcs are a blistering white-blue, not yellowish. this, to me, suggests much higher arc temperature. Good job

Zum Beispiel

Mon Feb 18 2008, 06:13PM

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

Nice! Pretty cool arcs from a flyback. You should try making a Jacobs Ladder.

Just one thing though: Don't use a screwdriver as a chicken stick. Sure, it might be just a flyback, but still. If you learn the proper safety procedures from the start, you won't do anything stupid with things that can actually kill you.

Plus, since it's on Youtube, it's good to set a good example. Then some random kid won't fry himself with a MOT.

EE2K11

Mon Feb 18 2008, 11:03PM

Registered Member #1218 Joined: Tue Jan 08 2008, 02:13AM
Location: College Station, TX
Posts: 9

Similar to this circuit minus the NPN/PNP totem pole between the 555 and the MOSFET gate and the resistor between the 555 output and the FET is 50 Î©. A 10k pot controls the frequency (adj from 12 kHz to 60 kHz). To clarify, there is a 1 kÎ© resistor between pins 7 and 8 and a 10 kÎ© pot between 6 and 7. I believe the capacitor is 10 nF. I could actually get higehr output voltages with a lower frequency (it is set pretty high in this video), but the primary likes to arc across to the secondary and melt the plastic

Running at 30 V input and drawing arcs I wouldn't run it for more than 30 seconds or so - it gets rather hot, both the 7812 and the FET share a heatsink.

[Edit: Image size]

Weston

Thu Feb 21 2008, 02:22AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

noob question: what is the pnp transitor for?

uzzors2k

Thu Feb 21 2008, 08:48AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Turning the mosfet off again.

Those are incredible arcs from the good old 555 driver EE2K11! When ever I use a flyback driver (single ended) I only get sparks and almost never arcs. Btw, have any of you found the multiplier/ internal capacitor connection? I've found almost all monitor flybacks have a pin which when grounded makes the sparks long and juicy. It's usually one along the side of the transformer, and not among the horseshoe pins.

Dr. Dark Current

Thu Feb 21 2008, 09:47AM

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

This is pretty cool! I can get "almost" unlimited power from th single ended driver by using a resonant capacitor across the FET, I was once getting some 15cm arcs from a DC flyback and ~200W but the arcs were purple, not hot and white as yours.

EE2K11

Thu Feb 21 2008, 11:27PM

Registered Member #1218 Joined: Tue Jan 08 2008, 02:13AM
Location: College Station, TX
Posts: 9

How can I modify this circuit for even greater output? What about a push-pull dual FET setup using a 555? I still have 5 more STW18NB40 FETs.

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