transformers for cheap low current flyback supply, +/- 45V ?

Are there any commodity ("cheap and easily obtained") transformers with which a low power flyback supply might be built? I have used the Unitrode UCC3843 -style PWM controllers before in a flyback circuit to get both positive and negative outputs, but always using custom (expoensive) transformers.

Does anyone have recommendations for a general purpose flyback transformer? I want to get output voltages of +45 and -45 VDC, at only

Now, about that transformer recommedation?

Look at my first post in this thread.

Hey MW... don't mind Phil. He's the resident troll, and 90% of us have him killfiled. He has very little useful information and a very large excess of "bollocks" (among other popular expletives he uses).

Tim

-- Deep Fryer: a very philosophical monk. Website:

"mw"

Just needs a tiny ( iron or ferrite) transformer with a centre tapped secondary and a ratio of about 1:10

If the input DC is regulated , then so will the output DC.

.......... Phil

"mw"

..... Phil

........ Phil

I suggest you design a circuit running at 250k to 1MHz frequencies, which means the transformer won't require many turns, and can be easily wound by hand. That way your transformers will be custom, but they won't be expensive. :-)

Use an dictionary if you have to.

.......... Phil

BTW, you do this with TI's cmos ucc38c43 controller ICs, or better.

I was beginning to get that feeling. :-)

Thanks, mw

Yeah, I was thinking about starting with a toroidal choke, and just adding turns of wire as needed. It seems like there ought to be a commodity flyback transformer on the market, but maybe I am out of date. That seemed to be a popular idea about 10 to 15 years ago, or at least the PWM chip salespeople were pushing it in their ads.

Thanks, mw

Most of us wind on bobbins, which are inserted into pot cores. For offline converters the plastic bobbin has two sections, separated by a divider, to insure good primary-secondary insulation. If your 12V input and +/-45V outputs share a common ground, insulated sections aren't strictly necessary. However, if your 12V is really a 13.8V car battery, complete with load-dump spikes, etc., then a fully insulated input-to-output setup may be a good idea.

Flyback pot cores usually have an air gap, to reduce core saturation and store the energy that's dumped into the output in the second half of the cycle. They're available in a wide range of sizes and ferrite formulations. You won't find ferrite pot cores at distributors like DigiKey or Mouser, but there are a few sources for hobbyists, such as Amidon,

To answer your question directly.

There is no such thing as a universal flyback transformer.

Every one has to be designed individually taking into account operational frequency, input voltage, power and desired output voltages.

Not like your 50/60 Hz transformer at all.

Go to

Graham

You omitted to say what frequency you want to use, what power level you need and what the line input voltage is for starters.

Graham

WRONG !

You need an air gap with a flyback design.

Go learn some basics.

Go to

No you're not engaging your brain.

Do you think transformers are the same @ 20kHz and 1MHz ?

No it never was.

Graham

"Tim Williams"

Williams one of the resident know nothing half wits.

A sleazy, ying little scumbag with s*it for brains.

On his good days, that is.

........ Phil

"mw"

Piss off - f*****ad.

........... Phil