isolated buck transformer

Thread Starter


Joined Sep 20, 2005
I am designing a power supply with two outputs, with isolated buck topology. For this I would require a three winding transformer.
Since two winding coupled inductors are readily available, is it possible to parallel the primaries and use it the same way?


Thread Starter


Joined Sep 20, 2005
i couldn´t get a better picutre, the two secondaries are isolted from each other. The question is if two transformers with primary in parallel will behave the same like one transformer with two secondaries?


Joined Apr 5, 2008

I know that paralleling of secondairies is done in power transformers.
This picture comes from a ILP transformers folder:




Joined Feb 8, 2018
Something called a "coupled inductor" is much more likely to be suitable for a flyback converter than any of the buck-derived topologies. Usually such parts are designed to store significant energy, which is contrary to the intent of a true transformer. Stored energy is a big problem, even when there isn't much of it. In a typical single-switch forward converter, for example, an extra winding is normally used for the express purpose of removing stored energy.

Coupled inductors are desirable in a buck-derived converter with multiple outputs to improve cross regulation relative to what would result with individual inductors for each output. For the best performance, coupling needs to be good, but not too good.

You couldn't use separate inductors with a common switch for a flyback for multiple outputs unless the loads were always nearly "effectively" identical.