LM5026: Using toroid transformer in DC-DC converter

Hi Aneesh

This is my opinion -

There is no fundamental reason why you cannot use a toroidal transformer, but there are a few practical ones.

Toroidal transformers are difficult to wind - especially power transformers with heavy wires

Likewise, it's impossible to add internal electrostatic screens from primary to secondary on a toridal transformer.

It's easier to control the primary-secondary capacitance, and how it is distributed across the length of the windings in a 'normal' transformer.

It's almost impossible to put a gap in a toroidal transformer - I know that a gap is not necessary in a topology like the active clamp forward but sometimes a small gap is used to give the transformer some ability to carry a small DC bias.

Toroidal transformers don't use bobbins, this means that the windings come off a toroid as wires rather than being soldered neatly onto the pins of a bobbin. - they can of course be mounted on a carrier plate of some form. Having pins on the transformer makes testing easier and makes assembly into the finished product faster, and less error prone.

There may be some second order effects relating to EMI - it's difficult to shield nearby components from electrical fields coming off the windings of a toroidal transformer - although the stray magnetic field from a toroid should be a bit lower than that from a 'normal' transformer.

I can't think of any reason why a toroidal transformer would be better and they are probably going to be more expensive for a given level of performance.

So - having said all that - please feel free to experiment.

Regards

Colin