> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of PicDude
> Sent: Tuesday, November 26, 2002 2:20 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [EE]: Custom transformer winding...
>
> Can anyone help me with winding a custom inductor/transformer.  The specs
> are as follows:
>    - Input = 29.38 uH, 31.35 mOhms

>    - Output 1 = 0.75 ratio, 54.49 mOhms
>    - Output 2 = 0.23 ratio, 7.64 mOhms
>    - Output 3 = 0.75 ratio, 140 mOhms
>
> Total power output = 20W, current at input winding should be 2A,
> and freq = 100kHz.
>
> How do I go about this?  First, how do I pick a toroidal core,

You need to select the material of the core to react at your frequency.
You then pick the size of the core to handle the flux density.
The primary reactance is 18.46 ohms, and the smallest ratio of reactance
to resistance is 1:4 so the driving generator must be 4.6 ohms or lower.
(Lower is better.)
If the generator is 5 ohms, it generates 10 volts @ 2 amps.

The Amadon catalog has the formulas for uH per turn per core.
It also has how to calculate Gauss. (AC and DC)
It also has tables for how much wire you can fit in a core,
the wire tables tell you how much parasitic resistance in the wire used.

Once you have correctly designed the primary,
the secondary is just winding ratios with different size wire.

> then the wire, etc?
>
> I have a link here (
> http://members.tripod.com/~schematics/xform/xformer1.htm ) that
> explains how
> to wind a custom transformer, but some parameters (like # of
> lines of flux)
> seem arbitrary, and I feel like I need something more calculated).  Using
> the sample lines of flux tells me my primary needs .031 turns of
> wire, etc.
> Is there a way to determine lines of flux, or another to design this
> transformer.
>
> Cheers,
> -Neil.
>
>
>
>
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  |  __O    Thomas C. Sefranek   WA1RHP@ARRL.NET
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