# Flyback Converter Transformer Leakage Inductance

We are in the process of designing an inverter , in which designing a step up flyback converter is crucial.

The problem, we initially faced was there were more step down transformers available than step up. So we planned to turn around the transformer and use it. Usually the manufactures give leakage inductance ratings for the primary side , now that we have inverted the transformer , we have ratings for the secondary. How do we use LT spice to find the desired leakage inductance. Is there any other way we could do this ?

## 1 Answer

How do we use LT spice to find the desired leakage inductance. Is there any other way we could do this ?

The simple answer is that if you know the turns ratio you can "move" the leakage inductance from one side of a transformer to the other by multiplying or dividing (as appropriate) by the turns ratio squared. For example, if the primary has a leakage inductance of 100 uH and has a step down ratio of 10:1 then that leakage inductance on the secondary side is 100 uH divided by $$\10^2\$$ = 1 uH.

If all you know about the transformer are the primary and secondary inductances (and I don't mean leakage inductances) then you can arrive at the turns ratio by taking the square root of those inductances. For instance a transformer with primary inductance 49 uH and a secondary inductance 1 uH has a step-up or step down turns ratio of 7:1.