# Understanding datasheet audio transformer

I am trying to understand the datasheet of this transformer: http://www.mouser.com/ds/2/449/XC-600133-202475.pdf

I have googled and found an answer about transformer datasheet (Understanding transformer datasheet), but it does not exactly fit the case I am looking at here.

My questions are (I quote parts of the datasheet in bold):

• What do those two sentences mean?:

Isolation voltage(primary to secondary): 100VDC min. @ 10MΩ

Insulation: >10MΩ @ 100VDC.

My understanding of the second quote would be that if there is a 100VDC component on the primary, then the leakage to the secondary is equivalent to a resistor of resistance at least 10MΩ. Is that right? What does the first quote means then?

• About the table with Impedance and Resistance. I think I am really confused here.

• First, I guess that the table data for Impedance are given at 1KHz because of the sentence Impedance variation: ±10% @ 1KHz. Am I right?

• Then I guess resistance is simply the electrical resistance of the primary and secondary of the transformer, am I right?

• Finally, what is the impedance that is given? Spontaneously, I would have guessed that since we are talking about transformers, that contain two coupled inductances, it would be $Z = \Im(L j \omega)$, where $j^2 = -1$, so that it would reflect the inductances of the primary and secondary. But this does not seem to be the case in Understanding transformer datasheet. If here also the given impedances refer to the case when loads are applied on the transformer, can I get the inductances from the datasheet? If not why are they not given? Is it irrelevant information in this context?

As a comment it feels like often, datasheets include data that are not really explicitly defined but which definitions are rather semi implicit, and dependent on the component considered... Not easy to understand then ;)

## 1 Answer

First, I guess that the table data for Impedance are given at 1KHz because of the sentence Impedance variation: ±10% @ 1KHz. Am I right?

Perhaps impedance ratio between primary and secondary was measured at 1 kHz.

Then I guess resistance is simply the electrical resistance of the primary and secondary of the transformer, am I right?

Yes, this makes sense.

Finally, what is the impedance that is given?
This gets a bit complicated. With the resistive source or load specified, a flat frequency response will result over a wide frequency range. Take the case of your data sheet first transformer: 10K primary to 2K secondary. With a 10K source resistance driving the primary, and a 2K load resistance on the secondary, you'll get a reasonably flat frequency response from 300 - 3400 Hz, within 3 dB. In this case, the 0 dB reference point was taken at 1000 Hz. At frequencies lower than 300 Hz, less power will be delivered to the 2K load. At frequencies well above 3400 Hz, AC power delivered to the 2K load drops off too. Sometimes a resonant peak occurs at this top end, especially if source and/or load resistances containing reactance are involved.
Nowhere is transformer reactance mentioned. It will vary over the design frequency range of 300 - 3400 Hz. AC losses due to transformer iron will vary too.

Bear in mind that the manufacturer specifies these transformers for audio use, and not for other applications. So specs refer tightly to this one application.