The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: John Popelish
Organization: This space not available for advertising.
X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: low loss transformer availability?
Date: Sun, 05 Jan 2003 03:21:24 GMT
NNTP-Posting-Date: Sat, 04 Jan 2003 22:21:24 EST
"Smile, it can only get WORSE" wrote:
> OK, I read all the comments and thank you all.
> Here's a reply to all the comments posted previously, forgive me for
> not posting separate replies.
> I need a transformer that has a high impedance input-so that it
> doesn't draw much current from the driver source when there is only a
> small load current being extracted from the secondary. I was hoping to
> operate at 3 mhz because it's easier to make a high impedance primary
> when the frequency is higher and 3 mhz is fairly easy to work with.
> In reality, I might be able to go down to 100 kilohertz or as high as
> 5 mhz.
This implies that you may have to build the best transformer you can
manage, and tune the source to the sweetest operating frequency.
> I need 12 V AC RMS in..... and (about) 120 V AC RMS out.
> Even when I chose a high mu toroid and wound with small wire, I could
> not get the impedance of the primary up high enough to prevent a lot
> of input current from being drawn by the primary when there was very
> little current being drawn by the load on the secondary.
High mu may imply low shunt resistance losses in the core. You may be
better off to increase the number of turns and go with a higher
frequency (high bulk resistivity) material or add more turns to your
present core to keep the volts per turn very low and the magnetic
excitation very low. At these low energies, low leakage inductance is
almost totally unimportant, and if you can pick your excitation
frequency, you may just be able to get the transformer into
resonance. Knowing the phase angle of the primary current would help
you to identify the cause of the dominant primary current (parallel
capacitance, effective parallel resistance in the core, parallel
inductance or hysterisis losses). If you can measure this phase while
sweeping frequency you may well identify the best frequency for a
given transformer design.
> I'm not sure whether this is due to standby loss, or whether it just
> means that my primary doesn't have enough reactance to prevent alot of
> current from flowing into it when the output load is light.
> Going down to .5 v AC RMS input makes the primary draw less current
> for the same load on the output, but the turns ratio is 24x (240 to 1
> instead of 10 to 1) higher and the secondary turns will have way to
> much capacitance coupling between the turns themselves (self
> It might be doable IF I could find a method of making a transformer
> that minimizes capacitive couplings between the secondary windings by
> mechanical design of the transformer.
Agreed. I would probably try completely separate windings
(sectionally winding the core) with the secondary having as many
spaced layers as would fit the core.
> My question to the group WAS:
> Does anyone have any ideas regarding how to make such a transformer?
> 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??
Do both ends of the secondary have to swing the same amount with
respect to ground (balanced output), or is the output single ended? A
balanced output should have a symmetrical secondary that has the
middle of the winding on the core, and two sections side by side in
series to keep the winding ends far from each other and the core.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup