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IRF540 mosfet sstc

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LAN_403

beserkolord

Tue Oct 30 2007, 08:29AM

Registered Member #1085 Joined: Tue Oct 30 2007, 07:43AM
Location:
Posts: 2

At the moment I'm working on an audio modulated sstc used IRF540 MOSFETs as the output devices.

Basically I'm building the coil for a school assessment. The problem I have encountered is that the teacher has limited my drivers operational voltage to 12 volts at a maximum of 10amps. I know from experience that its going to be quite a problem to get a decent spark at such low voltages.

My driver "The FETtosaurus" is based on richie burnetts Mosfet sstc. There is also parts from the plasmasonic driver. I am trying to find a way to properly match the drivers impedance to the secondary. But I can't bump the voltage up to far.

I am obtaining 24 volts for the mosfets by the use of a large voltage doubler.

So can you please have a look at my schematic and suggest any improvements I can make.
Believe me I'm not trying to make this project as simple or cheap as possible.

By the way I'm can't obtain any gate driver ic's so I'm employing the use of a push/pull pair.

forgot to put push/pull base resistors on original schematic

Driver module:
4hvdriver

MOSFET bridge
4hvbridge

Dr. Dark Current

Tue Oct 30 2007, 03:21PM

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

Wait, you cannot use a wall outlet?

Oh well, if you have only 12V available... I would suggest some lower voltage and lower resistance FETs so you don't waste too much power in your fets.

You can also use a step-up switching converter, the "mazilli" ZVS inverter would be great (simple&powerful) to boost your 12V up to something useable.

Ken M.

Tue Oct 30 2007, 04:12PM

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

Hmm for 12V's....if you could talk your instructor into letting you use 24V at 2-4A I'd say use the skori coil, it gives nice 2-12" from a coil that 8" tall on 2" dia with ~1050 turns.

Dr. Dark Current

Tue Oct 30 2007, 04:14PM

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

WhiteArc wrote ...

Hmm for 12V's....if you could talk your instructor into letting you use 24V at 2-4A I'd say use the skori coil, it gives nice 2-12" from a coil that 8" tall on 2" dia with ~1050 turns.

I think he said he wants to audio modulate it, which AFAIK is not possible with the skori coil.

ragnar

Tue Oct 30 2007, 04:32PM

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

Just about any topology will work fine at 12V, you'll get plenty of sparks if you can choose a suitable primary with not too many turns.

I've had 2" bushy discharges from one of my class-E drivers, with Vin = 12V.

Lomy

Tue Oct 30 2007, 07:28PM

Registered Member #789 Joined: Sun May 20 2007, 09:32AM
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Posts: 21

the best way for a 12v sstc is to build an e-class sstc with just 1 mosfet, a boostconverter from 12v to 200v and at last an interrupter. so you can play music over the interrupter ... ;)

perhops like this ? :

(under elektronik then sstc )

beserkolord

Tue Oct 30 2007, 08:51PM

Registered Member #1085 Joined: Tue Oct 30 2007, 07:43AM
Location:
Posts: 2

Thanks for the advice. Though the use of a 12v to 200v converter isn't permitted. The strict rules are a real pain.

About the MOSFET's I'm using an IRF540N bridge. The on resistance is 0.04ohms which really isn't all that bad. Anyway I using a voltage doubler for the bridge so the on resistance shouldn't
be too much of a problem.

I going to try to stick to a bridge because later on I'll probably power this up from a higher voltage. Something like 70volts.

I was thinking about the GDT's. seeming there only about 24 volts on the bridge.
Do you think its possible to think about direct gate drive without the GDT's.
This would probably help with the drive waveforms.

flannelhead

Fri May 30 2008, 10:06AM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Matt Bingham wrote ...

Just about any topology will work fine at 12V, you'll get plenty of sparks if you can choose a suitable primary with not too many turns.

I've had 2" bushy discharges from one of my class-E drivers, with Vin = 12V.

Tell me, how did you manage to do that?

Avi

Fri May 30 2008, 10:13AM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

if you turn it into a drsstc (you can run them cw at low voltage) you could get a hot enough arc you could pull out a few cm, it works well with audio

Dr. Dark Current

Fri May 30 2008, 11:31AM

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

Avi wrote ...

if you turn it into a drsstc (you can run them cw at low voltage) you could get a hot enough arc you could pull out a few cm, it works well with audio

I wonder how many primary turns qould be needed at 12V? 0.5? 0.3? Good luck making a one-thirdt-turn with good coupling

...

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