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Designing a transformer - RF Cafe Forums
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thrival
Post subject: Designing a transformer Posted: Thu Mar 13,
2008 8:38 pm
Lieutenant
Joined: Thu Mar 13, 2008 8:22
pm
Posts: 1
Hi.
I wish to build an oscillator of the
multivibrator type, for induction
heating experiments. The transformer
will be 1:1 with center-tap
on the primary. Frequency between 1khz
to 50khz. Needs to be
small as possible to fit on the PC board.
Now here's the rub;
needs to handle 115V-230V @ 1-10Amps, but should
run off as
little as 12V.
Torroids are fine, have the ARRL
Handbook 2008 and many online
L calculators but am still way over
my head. No idea what core material,
size, wire size, number of
turns, etc. Don't want to inductively heat
the transformer, just
the workpiece! Suggestions welcome, and
thank you.
l
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fred47
Post subject: multivibratorPosted: Fri
Mar 14, 2008 12:41 pm
General
Joined: Wed Feb 22,
2006 3:51 pm
Posts: 104
Hi!
You sure have some stringent
requirements.
Start with the simple ones:
Assuming your
output is 115-230V@1-10 A:
230V at 10 Amps is 2300 watts, so you'll
need a big core with thick wire.
At 12V input, this is about
192 Amps - so you'll need transistors rated for at least this much current.
Likewise, at 230 V input, your transistor should be rated for at least
500V.
200 A and 500 V transistors are rare and expensive, and
need special heat sinking and drive. You're into specialist territory,
not hobbyist or experimenter territory, if I've interpreted your requirements
correctly.
Good Luck!
Fred
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nubbage
Post subject: Posted: Mon Mar 17, 2008 6:36 am
General
Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location:
London UK
As Paddy once said: If I was goin thar I wouldn't start
from here.
I agree with Fred: 12V is the wrong starting point for
a system consuming more than 1kW, and using transistors is also probably
the wrong approach.
I would be thinking in terms of 56 volts at
least, and using Triacs, not transistors. The triacs would be driven
from a reliable DIL TTL or CMOS multivibrator 4047 or similar.
Why
12V?
Also you state the transformer is 1:1 ratio, but with a primary
of 12V and a secondary of 115V or 230V, the ratio would be more like
10:1 or 20:1.
Are we missing something here?
Posted 11/12/2012
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