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From: firstname.lastname@example.org (R.Legg)
Subject: Re: low loss transformer availability?
Date: 5 Jan 2003 09:56:59 -0800
NNTP-Posting-Date: 5 Jan 2003 17:56:59 GMT
> I know I can make a transformer that isolates the primary from the
> secondary (in terms of capacitive coupling between the windings-I've
> done it, it works great). But now I need to make a high turns ratio
> secondary that doesn't loose all the power through self-capacitance
> between the secondary windings.
> Any suggestions??
Try a split bobbin EP/RM or Pot core / former assy.
Use the largest core assy that will fit into your real estate, the
highest permeability material available with a polished core
interface. Keep this interface clean.
Your wire guage on the 120V side will be almost invisible, if your
real estate is low; use the smallest that you can physically handle.
Magnetizing current is inversely proportional to the turns count^2.
Wind the 120V section on one (of a double-section) or two outer (of a
triple-section bobbin)section. By filling these sections, you will
learn the number of turns required for the low voltage winding. Select
a guage of wire for the low voltage section that allows the required
turns to fit into the remaining section.
Terminate the high voltage winding with your minimum expected load.
Drive the low voltage winding with a low amplitude source to determine
the assembly's self-resonant frequency. If this frequency is higher
than you need, add load capacitance to drop it.
This will only be a low-power circuit if your driver is capable of
accepting reverse power transfer - make sure it has schottky
antiparallel diodes at the driving point.
You could do this the right way around, if you were willing to
indicate available real estate - you could even predict whether your
work was likely to succeed by running typical numbers on specific
candidate core sets, based solely on published Al, winding area and
wire guage. Some pot-core Q-tables might be instructive in determining
likely self-resonant frequency ranges.
Small toroids are impractical to wind with smaller wire guages and
larger turn counts. They are also difficult to isolate. If you were
interested in a test instrumentation grade of signal transformer, you
would consider going to that trouble on a physically larger specimen.
These are capable of considerable bandwidth.
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