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EvilTesla-RG

Tue Jan 31 2012, 07:04PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

I'm trying to build a Marx Generator, and I'm having a few issues with the Flyback Driver.

I started out by building the typical single transister 2N3055 driver (with 2 9v bateries).

This worked fine initialy, so I went ahead and built the Marx Generator, which after a few shots fried my driver. (not surprising).

So I went ahead and build a 555 timer driver. I used the schematics on this page: (also powerd by 2 9v)
Except I used a 2N3055 (on a heat sink) instead of the transitor in the schematic.

This worked okay, but it seemed to have less power than my previous driver. And it has also died. Using an ohm meter and an o-scope I have determined that it is the transistor that has burnt out. But I'm not sure if the flyback was drawing too much power through the transistor, or if the Flyback threw a HV spike back into the transistor.

So, I have a few questions.
First, any ideas as too why this driver gave out less power, when I thought it should have given out more?
And, of course, how can I keep my transistor from dying? As it appears that a Marx Generator is harder on the Driver than a streight Flyback (which makes sence).

Also, just a few side questions,
could I audio-modulate this driver by placing a transistor between the base of the 2N3055 and the 555 timer?
and I noticed that this driver was originaly designed for a SSTC, how good is this driver for an SSTC?

Thanks,
EvilTesla

Inducktion

Tue Jan 31 2012, 08:01PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Well, a 2N3055 requires a ton of base current to turn on fully. A 555 timer just can't supply the current necessary to do it.

Instead, use a mosfet, like an IRFP450. They require very little in the ways of current to turn on and your 555 timer driver will work much much better. Also, I recommend getting a better power supply than 9 volt batteries. They have high internal resistance, and....well, they just don't have the juice to drive flybacks right!

You can use a computer ATX power supply actually!

Or, if you don't have that, an old laptop brick will work too.

Big lead acid batteries are also some good choices.

Platinum

Tue Jan 31 2012, 08:35PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Have you thought of building the ZVS?

I was very noob at building circuits, I remember I couldn't understand the schematic for a 2N3005, but now I've rebuilt my ZVS driver. It can handle alot of power just make sure you use good capacitors and inductors.

Alex M

Wed Feb 01 2012, 08:14AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

For audio modulated arcs and control I recommend this one

audio is quite loud and you can choose the frequency it runs at via the potentiometer.

Use something like 4-5 primary coil turns for 24v input and perhaps less for 12v input as the half-bridge effectively half's the voltage the primary coil "sees".

You could build a ZVS if you wanted but you cannot audio modulate it and the lack of easy frequency control (imo) makes it get boring after a while. Plus the half-bridge doesn't seem to draw more than 3-4 amps when I run it on 36v from some lead acid battery's yet gives pretty decent results.

EvilTesla-RG

Wed Feb 01 2012, 04:24PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Interesting. Thanks for all your sugestions.

For now I think I'll stick to the 555 timer. It is simple and I know how it works.

(perhaps sometime in the future I'll try something more powerfull)

However, I'm curious why a Mosfet will survive where the 2N3055 burnt out. I don't really want to just throw anouther component into a circuit that I know will burn out components.

Thanks!

Inducktion

Wed Feb 01 2012, 07:13PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

The 2N3055 is a rather fragile component, even though it's pretty heavily rated.

MOSFET's tend to have reverse diodes, which help protect them against current/voltage spikes. Transistors don't have this.

MOSFET's are turned on fully by the 555 timer much more quickly and effectively than a large power transistor can be. That way there's a lot less heat dissipated in the switching device!

MOSFET's in general are just better for flyback drivers.

Daedronus

Wed Feb 01 2012, 09:16PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

Avalanche rated mosfets will survive the back emf spike you get at turn off that most certainly exceeds the voltage rating of the switching device (mosfet or bjt).
If you want the 2n3055 to survive you can place a zenner diode across it to clamp the voltage. Something rated above the in voltage but below the voltage rating of the 2n3055.

However, something like a irfp260 is vastly superior to a 2n3055.

And,

Use a tc4420cpa between the 555 and the mosfet. It's very simple to use and it will make a visible difference in the output power and it will lower the power dissipated as heat in the mosfet.

Alex M

Thu Feb 02 2012, 10:45AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Daedronus wrote ...

Avalanche rated mosfets will survive the back emf spike you get at turn off that most certainly exceeds the voltage rating of the switching device (mosfet or bjt).
If you want the 2n3055 to survive you can place a zenner diode across it to clamp the voltage. Something rated above the in voltage but below the voltage rating of the 2n3055.

However, something like a irfp260 is vastly superior to a 2n3055.

And,

Use a tc4420cpa between the 555 and the mosfet. It's very simple to use and it will make a visible difference in the output power and it will lower the power dissipated as heat in the mosfet.

IRFP260 still died from back emf when I tried it with the 555 driver.

Patrick

Thu Feb 02 2012, 12:07PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Alex1M6 wrote ...

IRFP260 still died from back emf when I tried it with the 555 driver.

Alex1M6, it is possible to easily exceed the 28mJ of max avalanche energy with the 555, in ways that are much less likely in a ZVS/ZCS type setup....becuase the 555 relies on inturrupting current (and the mazzilli types dont)
The trade off between the 555 types and the ZVS being how high the ultimate voltage gets... very low with the mazzili.

I used the 2N3055, and MJE3055T all the time way back in 1997-2000, i can affirm absolutly they are junk, especially since over the last 15 years we have so many good transistors both FETs and IGBTs, from many different makers.

Tetris

Thu Feb 02 2012, 05:06PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Woah! You can use a flyback for a marx generator? :O

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