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What transistor should i use?

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Plasmaarc452

Sun Mar 16 2008, 06:33PM

Registered Member #1394 Joined: Sun Mar 16 2008, 06:18PM
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I recently constructed a flyback charger for a bank of capacitors but i have a problem, the transistors i am using burn out if i put more than +12 volts at 1 amp.

I am looking for transistors on mouser.com right now but i cannot find one that fits the specifications. This website here http://www.angelfire.com/80s/sixmhz/flyback.html is what i am using for plans. The website is old and the transistors that the guy said to use are obsolete so i am trying to find a transistor that can match up to the specifications.

What i need to know
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Is an IGBT transistor the same as a regular Bipolar transistor because the only transistors that meet the specs are IGBT's.

Will a 500v 5amp transistor be enough for a 2-3 amp input on a flyback charger? (Or will it be more vulnerable to frying than a higher 10-15amp transistor?)
_________________________________________________ __________________________________________________ _________________

Please don't try and give me differnt flyback schematics, i know this is an inefficient circuit but it is simple and if it breaks it would only take me 20minutes to make a new one so thats why i am sticking with this schematic.

Dr. Dark Current

Sun Mar 16 2008, 06:39PM

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

Do you use original primary winding or external one?

If you use external (ie. you wound your own), the classic 2N3055 will work, or any other transistor which is at least 10A and 100-200V (not more- ask me if you want to know why).

If you use internal primary, the 2N3055 should work too but it tends to break by high voltage spikes, especially at higher voltages. In this case, try something like MJE13009 or similar.

You should also consider adding a ~0.22uF 400V foil capacitor across the primary winding, this often improves the output and decreases heating of the transistor.

wrote ...
Is an IGBT transistor the same as a regular Bipolar transistor because the only transistors that meet the specs are IGBT's.

NO. IGBT has a gate much like a MOSFET and it will not work in the simple feedback oscillator.

Hope this helps

Plasmaarc452

Sun Mar 16 2008, 06:55PM

Registered Member #1394 Joined: Sun Mar 16 2008, 06:18PM
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Thanks, i just put that part number in and i got a very similar transistor by the same manufacturer because that one was obsolete.

I got some MJE13009G transistors.

I am using a flyback that i pulled out of a crt monitor and 2 others that i got off of ebay, the windings are fully potted and they are rectified so i am using the regular windings.

The 2N3055 was what i was using because they sold them at radioshack and i could get them easily. Last time one of those burnt out on me it got so hot that it melted the solder on the leads (No lie). I will never use these again because of there low voltage rating of 100v meaning that they were susceptible to high voltage spikes which killed the transistor and there $5 price tag from overpriced radioshack.

What is a foil capcitor and how would i put that into the schematic? Does it require screwing with the windings or do i just put it on the primary winding pins on the bottom?

Dr. Dark Current

Sun Mar 16 2008, 07:03PM

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

Plasmaarc452 wrote ...

What is a foil capcitor and how would i put that into the schematic? Does it require screwing with the windings or do i just put it on the primary winding pins on the bottom?

The capacitor is not requied but for me it increased the output power.
Foil capacitor means it is non-polarised and not a ceramic (obviously), it should take high frequency currents well. You put it in parallel with the PRIMARY winding.
Try to search for type "X2" capacitors, they are cheap and work well for this purpose. For a start get a value of 0.22uF or 220nF. Then you can go bigger if it makes any difference.

One edit: The cap value is for the external primary winding (5-8 turns). In your case it could maybe decrease the output so if you don't want to mess with it, don't.

Plasmaarc452

Sun Mar 16 2008, 08:56PM

Registered Member #1394 Joined: Sun Mar 16 2008, 06:18PM
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Posts: 111

I will just stick with the regular setup.

Still i was able to charge a 100 joule capacitor bank in 30 seconds or less with 8aa's and a 2N3055 transistor.

I hope that if i connect a 2amp power supply at 12v or more the output will be increased so it can charge faster.

I have 6x 400joule capacitors and 2x 1 kilajoule capacitors so the higher the output the better. I want to be able to charge say a 400 joule capacitor in under 5 seconds. That is a big goal but i will be able to get there soon.

I really want to experiment with inductor charging, from what i can tell you have a huge inductor and a 555 timer that turns on an igbt very fast. I got the plans from anothercoilgunsite but i do not have a ferrite rod to wrap and inductor on. The guy that built it said that he could charge a 100 joule capacitor bank in 1 second with a 24vdc input.

Thats insane, if i could charge a bank that fast i could have a rapid fire coilgun at 60shots per minute.

Plasmaarc452

Sun Mar 16 2008, 09:04PM

Registered Member #1394 Joined: Sun Mar 16 2008, 06:18PM
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Posts: 111

I have a question, if i get a 12amp transistor and attach a heat sink and fan to the back of it would it be possible to run 5-10amps through it from a bank of lead acid lithium ion or lead acid batterys?

I am just looking to get an insane amount of power coming out of the flyback so that i can charge the capacitors as fast as possible.

Arcstarter

Mon Mar 17 2008, 03:20AM

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

Well if you want a good amount of power get a few irfp460's and make a 555 timer to run at resonant frequency. And the hook negative of an audio source to negative of power source and positive of audio source to pin 5 of the 555 and you have audio modulation(singing arc). Hope it helps!

Evilren

Tue Mar 18 2008, 12:17PM

Registered Member #1392 Joined: Sun Mar 16 2008, 05:00AM
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Posts: 4

I would recommend the IGBT's over the FETs for your application. Bipolars work but they need relatively sophisticated drive circuits to perform well, especially the High Voltage types. Arcstarter's suggestion is good, but you should also use a totem pole to drive the IGBT or FET. That way you'll get much more reasonable on/off times. You may want a better flyback for high powers, the secondaries on the TV types won't take much current at all.

If your using this for a coil gun then I assume your voltage on the capacitors isn't that high? say less that 1500V? There are much better ways to do this than that flyback.

Dr. Dark Current

Tue Mar 18 2008, 01:38PM

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

I say build the "zvs" driver. It can push several times the power of a 555+FET driver and is simple to build.

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