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

[mw]

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
10mA or so. Input will be 12V or so.

 

[Phil Allison]

"mw"

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
10mA or so. Input will be 12V or so.

** A simple square wave inverter would be far easier to make.

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]

So, then where do I get that transformer?

 

[Phil Allison]

"mw"

So, then where do I get that transformer?

** Try not top posting and I might help you.


..... Phil

 

[mw]

"mw"


** Try not top posting and I might help you.

..... Phil

Now, about that transformer recommedation?

 

[Phil Allison]

"mw"

Now, about that transformer recommedation?

** What is the app ?




......... Phil

 

[mw]

"mw"





** What is the app ?




........ Phil

Look at my first post in this thread.

 

[Phil Allison]

"mw"

Look at my first post in this thread.

** What is the application ?

Use an dictionary if you have to.



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

 

[Klaus Kragelund]

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
10mA or so. Input will be 12V or so.

Does it need to be isolated? And if so with PELV/SELV output?

Regards

Klaus

 

[Tim Williams]

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

 

[mw]

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).

I was beginning to get that feeling.

Thanks,
mw

 

[Phil Allison]

"Tim Williams"

"mw"

Hey MW... don't mind Phil.

He's the resident troll,

** Huh ?

Williams one of the resident know nothing half wits.

A sleazy, ying little scumbag with shit for brains.

On his good days, that is.



......... Phil

 

[Phil Allison]

"mw"

I was beginning to get that feeling.

** You are just another time wasting MORON !!

Piss off - fuckhead.





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

 

[Winfield Hill]

mw wrote...

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 (expensive) transformers.

Does anyone have recommendations for a general purpose flyback
transformer? I want to get output voltages of +45 and -45 VDC,
at only 10mA or so. Input will be 12V or so.

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.

 

[Winfield Hill]

Winfield Hill wrote...

mw wrote...

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.

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

 

[mw]

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

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

 

[Pooh Bear]

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
10mA or so. Input will be 12V or so.

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 www.powerint.com and read their app notes and get their magnetics
designer program.

Graham

 

[Pooh Bear]

Look at my first post in this thread.

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

 

[Pooh Bear]

Yeah, I was thinking about starting with a toroidal choke,

WRONG !

You need an air gap with a flyback design.

Go learn some basics.

Go to www.powerint.com and read *all* the app notes. That's how I finally
learnt the multiple subtleties of flyback designs.

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.

No you're not engaging your brain.

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

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.

No it never was.

Graham

 

[Winfield Hill]

mw wrote...

Yeah, I was thinking about starting with a toroidal choke, and just
adding turns of wire as needed.

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, http://www.amidoncorp.com/ who offer inexpensive bobbin-core
RF transformer sets, http://www.amidoncorp.com/aai_cost_potcores.htm
One would have to add thin spacers for best use of those as high-power
flybacks, because they're ungapped. But don't bother for only 900mW.