From: "Smile, it can only get WORSE"
Subject: low loss transformer availability?
Date: Sat, 04 Jan 2003 14:30:08 -0500
Organization: Posted via Supernews, http://www.supernews.com
X-Newsreader: Forte Free Agent 1.92/32.572
Good day all,
I need help with a transformer design, or perhaps just a nudge in the
My transformer needs to be small (physically), and have extremely low
standby losses. It will operate around 3 mhz in a linear AC power
supply (not switching mode). It's output capability will vary between
1 microamp and 150 microamps and it only needs to supply 50 milliwatts
of power. It should be capable of a 10 to one primary/secondary
voltage ratio (12 volts in and 120 volts out). Since the output
current is so small, a lot of secondary wire resistance is acceptable.
I'm told that toroids are ok, but they still have a lot of stray
capacitive coupling between the windings.
I need to make sure the input current is low when the load current is
minimal.... hence the interest in ultralow standby current (no
secondary load current should mean no (minimum) input current to the
I was wondering about alternative types of transformer
technology...such as planar. Or, perhaps a ferrite core could be
machined to allow power transfer into the core while creating
isolation between the windings?
I began my research with a signal generator and by plotting the input
current versus the output current with varying loads on the output. As
I got down to loads in the mid/high megohm range, I discovered that he
input was still drawing significant input current, which IS NOT what I
need. Perhaps I need a torroid based transformer with high input
impedance so that it doesn't draw much current without a secondary
load...but, I could not achieve this on the bench test setup.
Any ideas? Am I missing something?
PS: Please don't send me any switching power supply design messages.
My input is AC, my output has to be AC and I can't use switching mode