# How to calculate primary, secondary, and auxiliary inductance of this transfromer?

I am wondering how to calculate/find out the inductance values for primary, secondary, and auxiliary windings of a Würth Electronik 750310742 transformer. The main reason is so that I can attempt to model the transformer in LTspice.

The primary has an inductance of 38 uH and couples to the secondaries with a turns ratio of 2:1 and 2:1.1. The 2:1 coupling means that the secondary inductance is $$\(1:2)^2\$$ x 38 uH = 9.5 uH. The other secondary has a turns ratio slightly less (2:1.1) and therefore has an inductance of 11.5 uH.

You use the square of the turns ratio to gather inductance values for unspecified windings.

The leakage inductance for each secondary is specified as 0.47 uH.

• Thank you, good sir. What is the reason the ratio gets inverted for the calculation? – circuit_noob533 Sep 18 '19 at 14:44
• Any reason for the downvote? – Andy aka Sep 18 '19 at 14:49
• @circuit_noob533 fewer turns on the secondary means the ratio of turns on primary to turns on secondary is inverted. If you knew the secondary inductance the ratio wouldn't be inverted to obtain the primary inductance. – Andy aka Sep 18 '19 at 14:51
• Makes sense. thank you for the explanation. It is exactly what I needed. I am not sure why someone would downvote. I upvoted in order to cancel out. – circuit_noob533 Sep 18 '19 at 15:01
• @relayman357 yes, I'm describing the inductance that couples to each other winding. I mention the leakage inductance in my final sentence. – Andy aka Sep 18 '19 at 15:30