# Why is the LTspice transformer failing to step up?

I am simulating a basic pair of coupled inductors in LTspice. I have a 1HZ 2V peak AC wave on the input. The primary coil is 4uH with 1ohm parasitic resistance and the secondary coil is 20uH with 0ohm parasitic resistance. L2/L1=(N2/N1)^2 so we can say the turns ratio is sqrt(20uH/4uH)=2.236. However, when I simulate I find that the AC wave is stepped down from 2V peak to around 110uV peak which is very strange. Can anybody please help explain this?

• What is the L/R time constant of 4uH with 1 ohm ESR? Commented Jul 4, 2022 at 21:32
• For 1Hz you need a briefcase-sized inductor. Microhenries won’t cut it. Commented Jul 4, 2022 at 22:24
• @smitty you should take the 2 minute tour to understand why folk offer free help. Commented Jul 7, 2022 at 17:24

## 1 Answer

The primary coil is 4uH with 1ohm parasitic resistance

Here's the problem.

Your input excitation voltage has a frequency of 1 Hz hence, at this frequency, 4 μH has a reactance of 25 μΩ AND, the voltage developed across it IS NOT 2 volts peak but around 50 μV peak.

That is the voltage applied to your inductor that couples to your secondary so, with a turns ratio of 2.236 you get a peak output voltage of 112 μV: -

Look familiar?

When you have digested this you should take the 2 minute tour to understand why folk give their time for free and what you need to do to terminate this Q and A session. Please retrospectively apply what you learn there to your previous questions too.

• 25 μΩ, surely, not 25 μH? Commented Jul 4, 2022 at 22:42
• @Hearth oops yes and fixed. Commented Jul 5, 2022 at 6:31