Modeling transformer in Ltspice

Question

I am trying to model a transformer of 1:100 ration in Ltspice, here is the picture of it

The above circuit is stepping up the input voltage by 100 times but I see something strange which is when I am providing SINE 1V input with series resistance of 0.1ohm and freq of 1MEG then I am observing the following 1mV at input

and output voltage as 100mV which makes sense when the input voltage is 1mV

My question is why is the input voltage 1mV when I am providing 1V at the input? Can anyone please answer this question.

Answer 1

Your circuit shows a 1 ohm load on the output. This load is also seen at the input but 10,000 times smaller. So when you couple the ac source to the primary via a resistor of 0.1 ohm, there is a vast input voltage reduction on the primary due to the resistive potential divider action.

Think about this another way maybe. With 100V on the output, the power delivered to the 1 ohm load is \$\frac{V^2}{R}\$ = 10 kW. This power has to be supplied by the input voltage of 1V. To supply this power from a 1V source means a current of 10,000 amps into the transformer primary and the most current you can supply when a 0.1 ohm resistor is placed in series with the 1V source is 10A.

This means your primary voltage MUST reduce by a 1000:1.