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Improved single transistor flyback driver

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dingo27

Tue May 13 2008, 09:05AM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

maybe you could use CW multiplier...

Firefox

Tue May 13 2008, 06:31PM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

I could, but a CW would drop the overall output power, and I'm just trying to increase power without having to buy a new transistor. I guess I will have to find a variable power supply if I want to plug this thing in.

dingo27

Tue May 13 2008, 06:38PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

hm, what are you using as transistor? i built that cicuit twice, once with HV trafo from CRT screen (10-15 mm sparks) and second HV trafo by myself (4-5 mm sparks)

i was using 5 turns primary and 3 turns flyback... no capacitors etc. just transistor and 2 resistors

Mads Barnkob

Tue May 13 2008, 08:10PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I just tried with a MJE13005F transistor instead of 2n3055, as I have understood from the datasheets the MJE is a faster transistor with higher voltage ratings and about the same current and on values.

but for some reason the copperlanes on my veroboard connected to the primary winding glowed up red and burned my board pretty bad.

suddenly I am not that excited to try a mosfet on it, so I better ask first, would a IRFP250 be suitable?

Dr. Dark Current

Tue May 13 2008, 08:24PM

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

MadsKaizer wrote ...

I just tried with a MJE13005F transistor instead of 2n3055, as I have understood from the datasheets the MJE is a faster transistor with higher voltage ratings and about the same current and on values.

but for some reason the copperlanes on my veroboard connected to the primary winding glowed up red and burned my board pretty bad.

suddenly I am not that excited to try a mosfet on it, so I better ask first, would a IRFP250 be suitable?

This circuit will not work with MOSFETs as they have totally different gate drive requiremens.

To your transistor, as I said it sometimes does not work with >250V transistors because of different base structure. They usually work better with higher supply voltages and more pri. and feedback turns.
Have you tried changing polarity of one of the windings? The feedback may be of wrong polarity, so the circuit does not oscillate and your transistor is turned on all the time (shorting out the power supply).

Mads Barnkob

Tue May 13 2008, 08:32PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Dr. Monster Arc wrote ...

I reinstalled the 2n3055 to test the circuit and luckily its still working despite it looks like bombs were droppped.

you think that changeging polarity would work even though both transistors share pinout and are connected in the same way.

offtopic: a friend of mine raised a question about the resonance of the flyback would interfer with a tesla coils resonance if the flyback is used as the powersupply, say flyback runs at 15-50 khz vs tc at 400-800khz?

Dr. Dark Current

Tue May 13 2008, 08:45PM

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

MadsKaizer wrote ...

you think that changeging polarity would work even though both transistors share pinout and are connected in the same way.

In this case it won't work, like you say. The transistor is probably not good for the job

Firefox

Tue May 13 2008, 08:56PM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

My transistor is a Sanyo 2SC4106 (400V 7A) salvaged from a PC PSU that I blew out. There were two of them, and ironically I think it was this chip's twin that fried. Screwed to the heatsink it came on with lots of thermal paste, this transistor only gets hot after about 5 minutes of operation. Arcs start at about 3-5mm and can be drawn to about 12-14mm. Toying with the values of the resistors seemed to help/hurt the arc length a bit, but I don't have any brand-new parts, so both resistors are made from several 2-4W resistors soldiered together. This is all with a 4 turn primary, and a 2 turn feedback.

Mads Barnkob

Tue May 13 2008, 09:11PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Firefox, have you tried 8 turn primary / 4 turn feedback?

that setting worked out best for my flyback after trying alot of different settings. I can start arcs 15mm.

dingo27

Tue May 13 2008, 09:42PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

MadsKaizer wrote ...

offtopic: a friend of mine raised a question about the resonance of the flyback would interfer with a tesla coils resonance if the flyback is used as the powersupply, say flyback runs at 15-50 khz vs tc at 400-800khz?

i am running one TC with that... nothing happened, it is normal (an SGTC )

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