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HV Flyback Bench Top Power Supply for Lab.

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Patrick

Fri Jul 22 2011, 10:17PM

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

Proud Mary wrote ...

Are these 1GÎ© each ?

Each one is 15Mohm, 25kV, 2 watts, 5 inches long, tiger stripe with aluminum oxide core .3 inches in diameter. Id use two in series. thus 50Kv at 4 Watts as per the spec...

Killa-X wrote ...

Hopefully you get things figured with the pins. I have always ran them from the core, never the internal windings. But good luck! I have a flyback from a rear projection screen that is 2X the size of these, with a voltage multiplier. However, it has horrible arcs because the pins are too close and flash over.

Killa-X, Would you like to join the oil insulating mafia? I know a guy.

The pins 6 and 8 have a smaller wire awg than the 2 and 12 pins, but pins 6 and8 have the lowest reistance at 0.2 ohms others are at 0.4-0.6 ohms, so the primary of pins 6 and 8 would dissipate 5 watts given the switching wave as it is now.

Proud Mary

Fri Jul 22 2011, 10:29PM

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

Maybe you should consider XL @ 15 kHz, rather than R, when comparing the different winding options. So measure those inductances...

Patrick

Fri Jul 22 2011, 10:33PM

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

I killed my LCR meter (BK precision 875B), so i cant maesure X sub L.

Proud Mary

Fri Jul 22 2011, 10:41PM

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

Thinking about that 850 Vpp auto tap on the primary, you can expect quite a bit of back EMF looking for weaknesses in your driver circuit

Patrick

Fri Jul 22 2011, 11:27PM

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

Proud Mary wrote ...

Thinking about that 850 Vpp auto tap on the primary, you can expect quite a bit of back EMF looking for weaknesses in your driver circuit

Well ill up the gate protection then, my mosfet can handle 1000V, but Its TVSed down to 600V, STmicro always puts double zeners across the gate, but ill use a TVS there too.

The flyback (and the bottom pins) itself is pretty well insulated with the addition of epoxy and oil, so ill eat your best top hat if a spark or arc develops from the bottom pins... the semi's however are always a questin mark though.

EDIT: ive got the transistor/ heat sink up too 156 degree F... core to 110 F.

EDIT: the fall time (100% to 0%) seems to be between 800 nS and 1.2 uS i could probaly do better with a lower gate resistance.

EDIT: Fall time is 1.1uS (100% to 10%), so that gate drive IC is really working, as the 555 was only capable of 3.8 uS when directly connected to the gate.

New pic...

97degrees F, at the top surface of the acrylic tank. The small bubbles on the center and left are from the heat of expansion from oil filling the now hot ferrite gap, the larger bubble on right is for thermal expansion of the oil, the air bubble shrunk about 0.2 inches in overall diameter while at 97 degree F (ferrite is at 118 peak temp F). Time to let it cool off. I do worry that the pressure will blow out the gasket sealer.

EDIT: Its 9 PM, im too tired to continue, ive captured "a" high voltage scope screen shot, not sure how credible it is though. Shorted out the main capbank 4000uF @ 82 Volts across the drain-source, whole apartment smells like burned metal, oscilloscope was undamaged, im unharmed but pisst off. Im done for the night, time to drink new castle.

Whoops it just gave up the purple smoke! MOSFET is definitely KIA, had another 20 seconds of run time before it finnally died. Apartment stinks even more now. I had 12, 11 left now.

EDIT: 11:43 PM totally drunk right noW, no more hV for me. I have new pics to post.
HV scope pics...

Current pulse, zoomed in. 6.6V means 6.6V / 0.5Ohms = 13.2 amps.

Average at 10.8 kV (1000:1 Probe, 30.6M ohms) I have no idea if this is credible or bogus.

Peak at 24.4kV (1000:1 probe, 30.6 Mohms) I have no idea if this is credible or bogus.

_________________________________________ ___________________________________________

EDIT: 1:03AM .... neEd sLeEp....ZzZZzzzzzZzzZZZzZzzz....

Does any one know what a flyback output looks like on scope?
maybe on the last page of this PDF?

]flybackscope.pdf[/file]
From the above PDF and my Screen caps...

_________________________________________________ ___________________________________

>>>

Patrick

Sat Jul 23 2011, 10:43PM

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

All systems fixed, fully functioning now including fan and new Logic power cap. it wasnt the transistor that blew-out last night, it was the power resistor 0.5 ohm, stunk like hell.

EDIT: I think im boiling the oil around the primary, bubbles appear after 20 secs, and top of acrylic was warm, i think im pulling more current... the duty cycle is 53% now, i want to reduce it to 33% for heat control.

EDIT: Yep, boiling oil, i can see a hot stream of oil floating upward.

Patrick

Tue Jul 26 2011, 09:46PM

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

Ive decided to mod the primary as radhoo and ProudMary have previously pointed out. i will use pins 6 and 8 as my new primary, which is meant to see 65V. Ill be suppling 55-59V but im hoping the internal primaries reactance will limit the current to a value that wont cuase the oil to boil. If not, then ill turn the duty cycle down from 53% on to 33% on, for heat control.

EDIT: OOps I just blew the main resistor, the internal primary is way better at voltage and power. But I may have to ballast the primary with an external resistor, maybe in the oil tank.

EDIT: I have done the math, i now believe if i reduce the duty cycle from 53% to 40% reduces the power applied by 50%.... so ill try that tomorrow.

Proud Mary

Wed Jul 27 2011, 08:51AM

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

Patrick wrote ...

Ive decided to mod the primary as radhoo and ProudMary have previously pointed out. i will use pins 6 and 8 as my new primary, which is meant to see 65V. Ill be suppling 55-59V but im hoping the internal primaries reactance will limit the current to a value that wont cuase the oil to boil. If not, then ill turn the duty cycle down from 53% on to 33% on, for heat control.

EDIT: OOps I just blew the main resistor, the internal primary is way better at voltage and power. But I may have to ballast the primary with an external resistor, maybe in the oil tank.

EDIT: I have done the math, i now believe if i reduce the duty cycle from 53% to 40% reduces the power applied by 50%.... so ill try that tomorrow.

How about a nice little thermal shutdown feature?

Patrick

Wed Jul 27 2011, 09:21AM

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

Proud Mary wrote ...

How about a nice little thermal shutdown feature?

Im about to add that kind of feature in Gen 2 but the sparks and bad smell occured this time in just 2 seconds. So, i dont think a thermal interupt would be fast enough to intervene. Id really need pulse by pulse current limit on the order off 30-60uS.

EDIT: The 55 Volt pin 6 and pin 8 primary works well, definitley higher voltage.

Patrick

Fri Jul 29 2011, 08:26AM

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

New pics, case is nearing completion.

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