I have some questions regarding ideal transformers, similar to the one seen below:

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  1. When talking about 'ideal transformers', can I calculate the current on the primary side by finding the complex impedance of the primary side, then divided by the primary supply voltage. OR do I need to reflect the secondary impedance over to the primary winding taking the turns ratio into account?

  2. If the secondary winding was open circuit or had no series impedance, am I right in saying that the secondary winding will have no effect on the primary current? Hence the primary complex impedance over the supply voltage would give the correct primary current?

  3. In order to find Vout in a case like this where the primary supply voltage obviously doesn't equal V1, am I correct in saying I need to find V1 first in order to find V2. And the output voltage is simply V2 minus the voltage drop over the secondary series impedance?

Sorry for the questions, would just like some clarification before I move on



1 Answer 1


First noting that we are talking about ideal transformers...

You must first find the value of the impedance reflected back to the primary from the secondary side, then you can find the total impedance on the primary side. From this you can calculate the primary current, given the source voltage.

If your not sure what happens on the primary side if the secondary is open or shorted, think about what would happen as the impedance on the secondary got really, really big or really, really small. This will tell you what would happen if the secondary was open (\$Z = \infty\$) or shorted (\$Z = 0\$).

To find the output voltage you must first find either \$I_1\$ or \$V_1\$, then you can use the turns ratio to find the current or voltage on the secondary side. From that point the usual circuit analysis techniques apply.

  • \$\begingroup\$ Yes, thanks for your answer. This really clears up my questions. \$\endgroup\$
    – David777
    Nov 27, 2018 at 21:51

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