Hi Russell.  The short approximation is Zp=Vp/Ip = 220/13.6 = 16.1 ohms.  So 
your estimate is pretty close.  The more accurate way is:
Zp=?(R^2+?^2 L^2 ).  I think the skin effect at 100 KHz will modify R.  Even 
a small change can make a big difference.  Of course, it would be more 
important if Q was an important consideration. If R increases Q decreases 
because Q = X/R in the approximate.  I like to actually measure the 
impedance and compare it to the calculated value.



----- Original Message ----- 
From: "Apptech" <apptech@paradise.net.nz>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Saturday, August 09, 2008 7:20 AM
Subject: Re: EE


>>> I have to drive a transformer primary at 230 VAC @ 14
>>> Amps @ 100KHz.  I have not yet measured the primary
>>> impedance, but I will.
>
> The impedance you see will be about 16 ohms - ie the load,
> more or less regardless of the transformer's unloaded
> impedance.
>
>
>        Russell
>
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