Re: Very small step-up transformers?
- From: "Paul E. Schoen" <pstech@xxxxxxxxx>
- Date: Sat, 5 Apr 2008 02:17:37 -0400
"Tom Bruhns" <k7itm@xxxxxxx> wrote in message
news:7febb733-cf5f-4947-a384-a8a8e54d9321@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Mar 30, 11:21 pm, "joh...@xxxxxxxxxx" <joh...@xxxxxxxxxx> wrote:
Hi,
Does anyone know of an off-the-shelf miniature (1206 or 1210 sized)
transformer I can use for step-up, 3:1 or 4:1 ratio? Frequency is
low under 10 kHz and current is very low, < 20 mA .
I either find huge transformers or tiny RF / single-ended differential
ones...having a hard time with this one.
Thanks for your help!
What voltage? What source and load impedance? What's the lowest
frequency? Do you need isolation, or can it be an autotransformer?
MiniCircuits have some rated down to 4kHz, though not at 9:1 or 16:1
impedance ratio. Don't be put off by the fact they are listed as
"single-ended to differential." That mainly means the secondary is
center-tapped. Unless you are very concerned about primary-secondary
capacitances, exactly how it's wound probably won't matter a lot to
you. If isolation isn't important, you can stack the windings and get
3:1 voltage step-up with a 4:1 impedance ratio transformer. Expect
some loss, especially operating at the low frequency limit of the
part. Note that if you're operating at high impedance, things get
worse fast...1000 ohms at 20mA is 0.4 watts, and that's going to be
tough. 10 ohms at 20mA is 4 milliwatts, and that you can probably do
fine with one of the Minicircuits transformers rated for 50 ohm
operation down to a slightly higher frequency.
And...none of these is as small as 1210... Good luck on that one.
You could probably get one wound for you, if the voltage is low
enough.
Cheers,
Tom
Coilcraft has some small coupled inductors with 1:1 ratio, in a 4mm square
package http://www.coilcraft.com/pdfs/lpd4012.pdf.
They also have transformers for flyback converters, 4:1 ratio, as small as
12mm square http://www.coilcraft.com/misc/ga3372d.html.
But 1210 size is 3.2 x 2.5 mm.
They have a 2mm square single inductor
http://www.coilcraft.com/misc/DO2010d.html, and it looks like it would be
possible to add a second winding to make a transformer. Or maybe you could
stack a second one on top and get some coupling.
And they have a 5 x 6 mm gate transformer
http://www.coilcraft.com/misc/da23xx_gated.html with 2:1:1 ratio.
There is probably a better way to do whatever it is that the OP requires.
Paul
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