Planar in-depth

History of the Transformer

From the late 1800’s when theatres wanted a method of dimming their new lighting system, to the mid 1900’s when people wanted to be able to control the speed of their mode; train sets, right through to modern day telecommunication applications people have needed a means of controlling voltage from a standard mains supply. These systems have come a long way since the manual operated systems of the 1800’s, but the basic concept of the transformer has always been integral to the development of electrical and electronic sub-systems.


The transistor obviously provided great advantages to the world of electronics as we know it today, but for safety reasons it is the invention of the MosFet that really enabled the transformers to move on in the 1980s.

Not only do transformers provide a means for output voltage control, they are often also required to bestow current limiting features within a system. The size of these transformer units are inversely proportional to the switching frequency at which they operate, the higher the frequency, the smaller the transformer. In addition smaller transformers are able to provide higher efficiencies.

Historically, the capabilities and size of these units were limited by the frequency that the switching transistors were able to operate at 20kHz being the best one could expect. However, MosFets smashed this barrier apart, offering switching frequencies in excess of 250kHz. The limiting step of low switching frequencies had been removed from transformer design. This in turn was now replaced by the next limiting step namely the physical design of the traditional wire would transformer itself.

Planar Transformers

It is the planar transformers that overcome this new limiting step, resolving many of the problems of traditional wire would transformers. Not only do planar transformers provide significant reductions in the size and weight of your transformer design, but they also offer significantly improved efficiencies and much simpler manufacturing methods.

The name planar implies that the geometry of the transformer is more of a two-dimensional component, rather than the traditional three dimensional wire would equivalents. Planar technology comprises two major design features that distinguish it from the old fashioned wire would transformers.1) the windings are replaced by flat copper foil leadframes, and can even be embedded into a printed circuit board. 2) these flat windings are then mounted between thin & very lightweight ferrite cores.

Further to the obvious size and weight advantages, planar transformers also provide performance benefits through being electrically closer to an ideal component than their counterparts. All practical magnetic components introduce detrimental effects into the circuit in which they operate, which an ideal component would not. Planar components being closer to an ideal component remove the limiting factors in the performance of such circuits. They can often also save on additional components that may otherwise be required to overcome such problems.