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Portable transformer help! 11v to 800v

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Patrick

Sat Jan 22 2011, 02:15AM

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

I cant do it all for you, youll need to study some full bridge, half bridge, buck-boost, and push-pull type designs, then youll need to learn magnetic circuit theory if you want 10v upped to 800V at 500W.

I cant spare the time or effort to do it all, but now youve got a start.

read all of thed 20 or so PDF's that make up the TI/Unitrode posts for magnetic circuits at SMPS site ....

leodahsan

Sat Jan 22 2011, 02:38AM

Registered Member #3638 Joined: Fri Jan 21 2011, 11:56PM
Location:
Posts: 10

I know how they work and so, I even have a oscilator circuit ready here. Just need info: Frequency (HZ), Inductor/transformer specs (ferrite type/size, wires gauge and turns) and maybe some questions..
I'll search more tomorrow maybe, I'll post here if I find something important.

Thanks Patrick, hboy007 and bwang!

Patrick

Sat Jan 22 2011, 03:01AM

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

leodahsan wrote ...

I know how they work and so, I even have a oscilator circuit ready here. Just need info: Frequency (HZ), Inductor/transformer specs (ferrite type/size, wires gauge and turns) and maybe some questions..
I'll search more tomorrow maybe, I'll post here if I find something important.

Thanks Patrick, hboy007 and bwang!

You may be able to get a 555 timer to drive a simple transistor transformer arangement with no regulation or limiting, or modify an existing ATX for you needs, but the freq, magnetics/ferrite, drive, conditions number of turns/ parasistic capacitence/resistence, feedback-regulation... can all be the most difficult parts to get right.

Wolfram

Sat Jan 22 2011, 10:50AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Patrick wrote ...

Hold on let me see about the math.

leodahsan wrote ...

@Patrick
Yes, 247.6 (replace the commas with dots :P)
well you say R is 10 ohms? The ESR of the caps? They are all parallel, didn't tested the R but it is lower I think..

the charging circuit you will build will have resistence, this resistence will be in series between the Vsource, and Cbank, thus you will have an RC circuit, and a time of charge will be decided by that RC number. (IE.. V will go from 0% to 99% in 5RC's.)

Most capacitor charging circuit are constant current or constant power anyways, so they can't be modelled as an RC circuit. I don't think it makes sense to talk about apparent output resistance if you're charging a capacitor with a switchmode supply, just how much power it can deliver to the cap at any point.

Personally, I would use a circuit based on the very popular "Mazzilli" flyback driver, often also called the ZVS flyback driver. It delivers more or less constant current, if I'm not mistaken, so it's ideal for capacitor charging, and it's simple, bulletproof and can deliver a lot of power. For 800V you could wind your own secondary on a suitable gapped ferrite core, this shouldn't be too much work.

Pinky's Brain

Sat Jan 22 2011, 11:33AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

I've always wondered, why isn't the circuit in figure 9 from the following page popular? Less efficient than a resonant ZVS converter, but even simpler.

Steve Conner

Sat Jan 22 2011, 11:45AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Don't know, it looks like a good circuit.

I've seen it used once as a fluorescent lamp driver, and contemplated using it myself for one circuit at work, although in that case the current needed was so small that it worked out easier to just use a plain boost converter with a MJE340 as the switch.

Years ago, I made a really good capacitor charger using the transformer taken from an ATX PC power supply. These have a 160V primary, and a centre-tapped secondary to generate the 5 and 12V rails. I wired the secondary up as a Mazzilli oscillator using the centre tap and 5V taps, and fed the primary into a full-wave doubler with undersized capacitors to limit the charging current. (The Mazzilli oscillator gives a sine wave, so capacitors work fine as a ballast.)

It drew 10A @ 12V input and would charge 1500uF to 350V in a few seconds. For 800V, I guess you could put a 4-stage multiplier on the output.

The schematic is somewhere in the archives. I haven't been able to find it.

A capacitor charger can't be modelled as a RC circuit, because if it had a R, it would be 50% efficient.

Wolfram

Sat Jan 22 2011, 01:17PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Steve McConner wrote ...

The schematic is somewhere in the archives. I haven't been able to find it.

Here it is

Steve Conner

Sat Jan 22 2011, 01:32PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Thanks Anders! The circuit I was referring to is this one:

leodahsan

Sat Jan 22 2011, 03:15PM

Registered Member #3638 Joined: Fri Jan 21 2011, 11:56PM
Location:
Posts: 10

Thanks for all answers, I'm out of time NOW so I haven't looked all links (for now.. I'll look in a couple hours).

@Steve McConner
Can the voltage be changed? By adding more diodes and caps for a full wave rectifier...

leodahsan

Sat Jan 22 2011, 10:51PM

Registered Member #3638 Joined: Fri Jan 21 2011, 11:56PM
Location:
Posts: 10

Hi all again, I'm reading and checking all replies that I've found. Btw, my father found that for me:

Is it useable, if the 2n2222 gets replaced with a very high power transistor, and the flyback rewound?

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