What is a planar transformer?

A planar transformer is essentially a transformer that uses flat windings, usually on a printed circuit board, instead of copper wire to form the coils.  The PCB construction creates a different form factor that offers some unique advantages and a few tradeoffs.

What are the advantages of planar transformers?

The form factor of planar transformers offers several advantages, including:

Low profile – the windings are flat, allowing a shorter winding window. This can also mean the core can be designed for a larger cross-sectional area and greater surface area on the top and bottom to facilitate removal of heat from the transformer.

Excellent repeatability of construction – the PCB windings are very repeatable, which makes the parasitic effects such as leakage inductance and interwinding capacitance more predictable and repeatable.

High isolation – The PCB construction allows increased insulation between winding layers.

High-efficiency (typ 99% +), in a lightweight compact form.