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Determine impedance of xfmr circuit TRAN

Altair Forum User

This is a simple circuit but how does one get the correct impedance data at the xfmr input? Setup is just a 12.5ohm load, an ideal xfmr with N=2:1, and a sin source. The impedance should be 50ohms but what I get from the simulator is Vin and Iin. I want to determine V/I but how? Tried FFT but it looks good for V signal only but how to do that to the current? What I want to do is be able to take the FFT and V and I, get mag/phase for both and then I can determine Z by using V/I.

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Altair Forum User

Hi Dennis,

That seems to be the complicated way of doing it. try this demo where are use the RMS elements to extract the fundamental and the divide to get Z. The result is 50 ohms. If you want to do FFT, simply plot with the voltage and current time domain wavefroms and click the FFT button any waveform that is displayed will convert

Altair Forum User

Hi Albert,

This is helpful for sure but how does one get the impedance in terms of real/imag? So for instance, if you added a series inductor (100nH) before the ideal xfmr the impedance should go from 50ohms to 50+j*8.52 ohms. How does one find the reactive part?

Altair Forum User

Hi Dennis,

Try this circuit, it will calculate Z and then measure the lag of the zero crossing from voltage and current and then use this to calculate the angle. The angle is then used to break Z apart in to its R+jX form.