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Flyback (collaboration) for Corona, Insulation, Waveform purposes.

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Patrick

Sun Mar 06 2011, 04:08AM

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

OK, here we go...

Purpose: This device will replace my NST and Iggies for corona production, solid and oil insulation chartacterising, and O-scope waveform viewing, and cool pics---possibly burning stuff for fun too.

Implementation: A 555 timer configured for independent high and low driving of a IGBT or MOSFET, switching About 50-60Vdc at 2-3 Amps through the after-production primary.

GOAL: Hopefully 30kV at 200 Watts or there abouts.

Good 555 timer circuit site.
]htg7n60a4d.pdf[/file] IGBT
]stw13nk100z.pdf[/file] MOSFET

555 PWM indepentent high and low. From the above cited web page.

Initial build, aluminum Plate: 7.5" x 7.5" x 0.25"

35kV flyback, crack should not matter as the core is gapped anyway.

I'm considering cutting these pins to half hieght, then epoxing them in. I tried to solder "Ball" that lead such that the field intensity will be reduced due to lack of sharp solder points.

I will start with 10 turns, at 60 volts, im sure it wont take much on-time to cause saturation. Eventually I will enclose this whole flyback in acrylic and an oil tank.

Flyback, Cap bank, LV transformer (60Vdc @ 2A), TO-247, Bridge rect, and 555 PWM--PCB.

Flyback (1 of the 3 I bought from Killa-X)

Inducktion

Sun Mar 06 2011, 05:48AM

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

...why not use a half bridge driver? Or is that what the 555 timer is achieving?
If you use a resonant capacitor the output should be a bit higher, depending on the resonant frequency and the frequency output by the 555 timer. A half bridge version of this should work too. Why not use a GDT or something? o:

Patrick

Sun Mar 06 2011, 05:54AM

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

Inducktion wrote ...

...why not use a half bridge driver? Or is that what the 555 timer is achieving?
If you use a resonant capacitor the output should be a bit higher, depending on the resonant frequency and the frequency output by the 555 timer. A half bridge version of this should work too. Why not use a GDT or something? o:

Trying to keep it simple for first device version, but would a push-pull / half bridge do any good with diodes in series throughout the secondary?

Killa-X

Sun Mar 06 2011, 06:53AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Well, good luck with the project! Let me know if that core starts to cause any issues though. I may plan a 3 series ZVS someday but I will keep a track on your progress and see if I will try it my self for fun!

uzzors2k

Sun Mar 06 2011, 10:06AM

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

Patrick wrote ...

...but would a push-pull / half bridge do any good with diodes in series throughout the secondary?

Not really, you're better off driving these diode split flybacks in flyback mode. Push-pull should be used with full-wave or unrectified flybacks.

Sulaiman

Sun Mar 06 2011, 10:26AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I see two major reliability problems;

200W @ 30 kV = 6.66 mA = overheated secondary winding (3 mA/90W is ok)

driving the lopt primary with a symetrical primary waveform will produce a symetrical secondary waveform, so the stress on the internal diodes is 60 kV total (more with internal 'ringing') = over-volted diodes.

Since you're in the land of 110 Vac (or thereabouts) full-wave rectified mains is perfect for supplying a lopt in conventional flyback mode (as they were designed for)
You will need to isolate (pulse-transformer or opto-isolator) the lopt primary drive circuitry from your low voltage drive circuitry (555 etc.) and connect the 'bottom' end of the secondary to a reliable earth (Protective / mains earth) for safety and ease of experimenting.
With a couple of divide-by-two flip-flops you can drive four lopt with a mark:space ratio of 3:1
(this provides four pulses per 'cycle' for low output voltage ripple)
driven at variable frequency for output power control. This would give 200W RELIABLY.
Don't forget that when there is little load on the output the power that you're driving into the lopts has to go somewhere. I would put a fast >1500V diode from each primary to a 200W voltage clamp, I'd use 20 parallel strings of 3x1.5KE350CP TVS because I've got a lot of them, you would need something equivalent
(e.g. zener diode string to the base of a transistor that can take 200W @ 1.5 kV)

Patrick

Sun Mar 06 2011, 02:53PM

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

Uzzors wrote ...

Patrick wrote ...

...but would a push-pull / half bridge do any good with diodes in series throughout the secondary?

Not really, you're better off driving these diode split flybacks in flyback mode. Push-pull should be used with full-wave or unrectified flybacks.

I will be using the normal single switch flyback mode with TVS's, as I dont want my internal diodes blown out...I see no need to use a symmetric +,- waveform.

James

Sun Mar 06 2011, 08:12PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Don't forget to use a snubber when driving these things hard in flyback mode. There's a good app note here:

Note that quite a lot of power can be dissipated by the snubber. I once used a 60W 120V incandescent lamp in place of the resistor and was able to light it brighter than full brightness from about 40V into the circuit. Measured 76kV out of the SVGA monitor flyback though.

Inducktion

Sun Mar 06 2011, 10:00PM

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

Uzzors wrote ...

Patrick wrote ...

...but would a push-pull / half bridge do any good with diodes in series throughout the secondary?

Not really, you're better off driving these diode split flybacks in flyback mode. Push-pull should be used with full-wave or unrectified flybacks.

I meant using a half bridge driver so that you have two mosfets sharing the load equally. It would reduce strain on the fets and allow for more power right?

Patrick

Mon Mar 07 2011, 03:13AM

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

New work

7" tall acrylic oil tank, insulators, and flyback. Also seen, 75 M ohm 20kV resistor.

Does anyone know how well acrylic resists surface carbon tracking? (relative to other plastics: good, fair, poor?)

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