Planar Transformer Guide


To address an ever-increasing demand for more power in less space, designers are turning to Planar Transformers as an attractive alternative to conventional core shapes where low-profile magnetic devices are required.

These devices provide functions critical to the effective operation of DC-DC converters and have a greater consistency of performance than traditionally wound devices.

What is a Planar Transformer?

A planar transformer is a flat, low profile transformer fabricated using PCB technology. The basic construction method of a planar transformer consists of creating a multi-layer printed circuit board. These windings are then placed in low profile, E/E or E/I ferrite core combinations.

Planar transformers provide the electrical isolation, voltage transformation and energy transfer functions of conventional wire wound transformers in a smaller surface mount device footprint.

Planar Transformer Construction

Planar transformers fabricated on PCB comprise the following elements:

Planar Transformer vs. Traditional Wirewound Transformer

ParameterPlanar TransformerWirewound Transformer
ConstructionWindings etched as tracks on PCBWindings made from insulated wires
CorePCB dielectric materialFerrite, iron alloys, etc.
SizeExtremely compact and low profileLarger, significant height
Leakage InductanceVery low due to tight couplingHigher due to poorer coupling
Parasitic CapacitanceLow as limited overlapping areaHigh due to more overlapping wires
AC ResistanceLow as wider copper tracksHigher due to thinner winding wires
Turns Ratio RangeTypical 1:1 to 1:5Wide – 10:1 or more
Power LevelsLower – less than 10W usuallyHigher power handling capacity
CostLower due to PCB processHigher labor for hand winding
IntegrationExcellent, embed directly to PCBModerate, but requires mounting
RepeatabilityVery consistent and controlledPoorer tolerance and unit-unit variation
Efficiency>90% in well designed planar transformers>95% in conventional transformers

Advantages of Flyback Transformer



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