Transformer Primary / Secondary Impedance

As far as I understand transformers have no impedance, rather a percent impedance which is actually a voltage, expressed as a % of rated voltage, that is required to circulate rated current through the transformer. I also understand that transformers transform impedance according to the square of the turns ratio.

When looking at digikey transformers, there are parameters “primary impedance”, and “secondary impedance”.

Are these supposed parameters supposed to be interpreted as:

  1. Two parts of the impedance % ratio (i.e. primary=200k secondary = 1k)
  2. My desired/expected input impedance (primary) and output impedance (secondary). For example if i selected 200k as primary impedance, this means I intend 200k to be the range of impedance of the device being hooked to the input of the transformer.

Thank you for your help,

Welcome to the forum.

All types of electronic components have an impedance, often the AC and DC impedances are different, they can be difficult to measure/calculate, and/or they are not needed for using the component in an ordinary design.

Often with power transformers impedances are not specified at all, only the voltage/current ratings of the primary and secondary windings and operating frequency range are given. Usually that is all you need to successfully design it into a circuit.

For impedance matching transformers the impedance specs for the primary and secondary windings are essential. If you want to match a Hi-Z 50k ohm audio circuit to a Low-Z 600 ohm audio circuit you better buy a transformer that specifies 50k and 600 for the impedances.

AFAIK, percent impedance is a specification that is typically only used for large power distribution transformers. (I’ve never designed a system with them, so have no practical experience) See