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

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Newton Brawn

Tue Mar 08 2011, 10:43AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi Patric:

Thanks for tjhe 555 site.

Can you shou the complete schematic that you have in mind?

Regards

Proud Mary

Tue Mar 08 2011, 11:48AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Patrick wrote ...

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

Ionic surface contamination (e.g. fingerprints) and ionizable inclusions are the usual suspects in tracking failure, whichever dielectric is used.

But don't take my word for it! Google comparative tracking index and get your DIY lobotomy kit absolutely free of charge!

Patrick

Tue Mar 08 2011, 08:28PM

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

Newton Brawn wrote ...

Hi Patric:

Thanks for tjhe 555 site.

Can you shou the complete schematic that you have in mind?

Regards

Yes after my calculus homework is done, i will put up the schematic.

Patrick

Thu Mar 10 2011, 04:37AM

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

Schematic:

OK, everybody check my work, polarity and stuff. I was less than sober while putting this together.

First, on the 555 the pins 4 and 5 are left unconnected. I havent decided what to do with those yet.
Second, the TVS's are hopefully pointed right.
Third, R3 and R4 are pots, the R2 and C3 have not been fully decided yet.
Finnally, the Q1 device would be a common N-channel Mosfet ot IGBT.

So find my errors and make suggestions now before I commit to etch the board

Antonio

Thu Mar 10 2011, 01:03PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

D5 cannot be there. It will eliminate the necessary flyback pulse. The usual solution there is a fast diode from the drain to a parallel RC circuit connected to the power supply. A voltage limiter can be put in parallel with the RC circuit.

Patrick

Thu Mar 10 2011, 03:15PM

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

Antonio wrote ...

D5 cannot be there. It will eliminate the necessary flyback pulse. The usual solution there is a fast diode from the drain to a parallel RC circuit connected to the power supply. A voltage limiter can be put in parallel with the RC circuit.

D5 is a TVS invisible until in 600V, are you sure the flyback pulse will exceed 600 V , for a 10 turn primary? or do you mean it's hold off should be bidrictional?

Antonio

Thu Mar 10 2011, 04:24PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Patrick wrote ...

D5 is a TVS invisible until in 600V, are you sure the flyback pulse will exceed 600 V , for a 10 turn primary? or do you mean it's hold off should be bidrictional?

The diode in this position will clip the pulse at the drain of the switching transistor at the power supply level, not at 600 V. A bidirectional device will work.

Patrick

Thu Mar 10 2011, 05:19PM

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

OK, yeah i see your point, is this and improvement? 600v held off in either direction, before clipping.

@antonio:

Antonio wrote ...

The usual solution there is a fast diode from the drain to a parallel RC circuit connected to the power supply. A voltage limiter can be put in parallel with the RC circuit.

Can you show me an example? i fail to understand.

James

Thu Mar 10 2011, 08:15PM

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

Patrick wrote ...

OK, yeah i see your point, is this and improvement? 600v held off in either direction, before clipping.

@antonio:

Antonio wrote ...

The usual solution there is a fast diode from the drain to a parallel RC circuit connected to the power supply. A voltage limiter can be put in parallel with the RC circuit.

Can you show me an example? i fail to understand.

Look up RCD snubber. There are lots of application notes out there. As power levels increase though the snubber can dissipate large amounts of energy. I tried once using a 60W incandescent lightbulb as the resistor and could easily light it full brightness with about 40V going into the circuit.

Antonio

Thu Mar 10 2011, 09:03PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

If the load is not constant and there is no feedback, it's better to use something that recycles the energy in the transformer primary if it is not used in the secondary.
This is a flyback circuit that I made some time ago with an RCD snubber:

The resistor R3 was eating a lot of power. This is a modified version that worked much better, with C3 and D3 returning unused energy to the power supply:

Don't look at the switching transistor driving circuit, that is very inefficient and has insufficient base current capability for that transistor.

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