I would like to see how well a sine wave would pass thru a transformer. (from primary side to secondary)

Is it possible/practical to test small transformers which you might find in small low powered consumer devices with a signal generator and an oscilliscope?

sample transformer:


if so, is it really just connecting the signal generator (sine wave) to the primary, and the oscilloscope to the secondary?

(assuming the windings ratio would not blow up anything)

  • \$\begingroup\$ You probably want to connect a selection of different loads to the secondary as well (10k, 1k, 100R resistors for basic low power tests) in parallel with the scope probe. How a transformer works, with and without a load, are slightly different especially at high frequencies. \$\endgroup\$
    – user16324
    Feb 25, 2020 at 12:14

1 Answer 1


Yes, you can perform a basic test of a transformer by injecting a sine wave into one side and monitoring the other side.

Keep the frequency in the ballpark of what the transformer was designed for.

Pick a transformer that doesn't have a giant turns-ratio. Otherwise, if you stepping down, the voltage will be small and difficult to measure accurately.

If you use the transformer as a step-up, be careful. There probably isn't enough current to be dangerous, but you might get an unpleasant shock.

I would use a transformer with wires instead of terminals.

Note that this is only a basic test, you won't be testing many of the important parameters of the transformer (saturation current, ...)

Edit: I just tested a transformer that I have. It is rated: 115 VAC to 6.3 VAC, 4.8A.

With a function generator, 10 Vp-p in yields 0.668 Vp-p out. A ratio of 14.97.

Using the transformer ratings: 115/6.3 = 18.25.

Why the difference? The function generator test is unloaded. This is a good indication of the turns ratio. If I were to put 115 VAC into the transformer and load it with 4.8A, the ratio would be closer to 14.97.


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