What do I measure voltage in the output of a SM transformer in SMPS circuit?

In a working circuit I am getting practically very little voltage difference across the SM transformer output unlike a normal transformer. For this I can't understand how the SM transformers work in a SMPS circuit, and also I couldn't find proper study guide or explanation to understand. It will be helpful to have some assistance, thanks.

The peak voltage across the transformer has to be larger than the output voltage for the SMPS to work. However it will be a very non-sinusoidal voltage and the frequency will be 20 - 200 kHz. Multimeters won't normally be able to measure that frequency.

There will be DC current flowing which depends on the load, so there will be a really small DC voltage across the resistance of the winding, but with only a few turns of secondary winding that will be too small to easily measure unless there is a load.

You could look at this post for an explanation of how one type of SMPS works. There are lots of variations, so if you can post a picture or schematic, that would help.

Diver300 said:

However it will be a very non-sinusoidal voltage and the frequency will be 20 - 200 kHz. Multimeters won't normally be able to measure that frequency.

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That would be my guess also. What frequency are you trying to measure and what instrument are you using to measure it?

Ron