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Custom Planar Transformers and Planar Inductors

ConverNova is a planar transformer manufacturer based in Madrid, Spain. We design and build custom planar transformers and planar inductors for high frequency power electronics, with the windings on your main PCB, on a dedicated winding board or in stamped copper. We also tell you when a wound design is the better choice. Prototypes in 4 to 8 weeks, no minimum order quantity.

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The basics

What is a planar transformer?

A planar transformer replaces wire windings with flat copper traces on stacked printed circuit boards or stamped copper sheets, assembled around a low profile ferrite core. Because the windings are defined by the artwork, every unit has the same geometry, so leakage inductance and losses repeat from prototype to production. The trade-offs are higher interwinding capacitance and less flexibility once the board is made.

When it wins

Planar is a trade, not an upgrade.

It is the right answer often enough to be worth knowing, and the wrong answer often enough that we will tell you when it is.

Where planar wins

High switching frequency, where the copper can be thin and the skin depth stops punishing you. Low profile, where height is the constraint and not footprint. High volume, where identical units matter more than the cheapest possible bill of materials. And resonant converters, where a repeatable leakage inductance is worth real money.

Where wound wins

Below roughly 100 kHz, where the copper has to be thick and a PCB is an expensive way to carry it. High isolation, where the layer to layer spacing a planar needs eats the advantage. Low volume, where the tooling does not amortise. And anywhere interwinding capacitance is already your problem. Then a wound custom transformer is the better part.

Power density

When the box is fixed before the circuit is.

A rack power supply is a height problem before it is an electrical one. The slot is one or two rack units and nothing negotiates that, so the target arrives as watts per cubic inch and the magnetic has to be designed to the box rather than chosen from a catalogue of boxes.

Why planar, here

The winding height is the stack-up, and the stack-up is something you decide rather than something you discover. Layer count, copper weight, prepreg and interleaving are all written into the artwork before anything is pressed, so the part that comes back is the height you asked for. It is the same argument in AI data centre supplies, in telecom rectifiers and in any high density industrial supply where the enclosure came first.

What we need from you

The enclosure, if it is already drawn. Height, footprint, keepout zones and where the air goes decide more of this design than the turns ratio does. Infineon's 8 kW high frequency, high power density supply for data centre racks sits in our reference design index alongside fifty nine others, and every one of them reached the same place: the magnetic was a volume target before it was a component.

Construction

Three ways to make the winding.

The choice drives the cost, the current capability and how much of your board you get back.

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On your PCB
The winding becomes layers of your main board. No separate part to buy or place, at the cost of layer count and of a board that now has to be qualified as a magnetic
Winding board
A dedicated multilayer PCB carrying only the winding, assembled with the core into a discrete component. Keeps your main board simple and the magnetic testable on its own
Stamped copper
Thick formed copper turns instead of etched traces. Where the current is too high for a reasonable copper weight, this is what carries it
Cores
Standard planar E, EI, ER and EQ ferrite sets, and custom machined geometries where the standard window wastes space. More on core materials
Interleaving
Layer order set in the artwork, so the leakage inductance you measure on the prototype is the one you get on unit ten thousand
Isolation
Layer spacing, prepreg choice and creepage are designed to the standard you qualify against.

Construction

Planar construction.

Core halves closed over a stack of printed winding boards, with the leakage inductance fixed by the artwork.

Planar core halves closed over a stack of printed winding boards
An encapsulated planar transformer on stacked printed winding boards, with pin terminations and the core material marked

Straight answers

Planar magnetics, the usual questions.

When is planar the right choice?
When the switching frequency is high enough that the copper can be thin, typically above about 200 kHz, and when height is constrained or the design has to repeat identically in volume. Below roughly 100 kHz a wound transformer is usually smaller and cheaper for the same loss, and we will say so.
Why is the leakage inductance so repeatable?
Because the winding geometry is fixed by the artwork, not by how the wire lay. Every unit has the same interleaving and the same layer spacing, so the same leakage. That is what makes resonant converters reproducible in volume.
What is the catch?
Interwinding capacitance. Primary and secondary sit close together over a large area, which is good for leakage and bad for common mode noise. Layer order, shielding and the insulation system are how we manage it, and it is a conversation worth having early.
Can you use my own PCB?
Yes. Windings can go into your main board, onto a dedicated winding board, or into stamped copper. We can design the artwork and the stackup, or work to yours.
What is the difference between a planar and a wound transformer?
A planar transformer uses flat copper layers on PCBs instead of wire. It gives a lower profile and very repeatable leakage inductance, and it wins at high frequency and high volume. A wound transformer gives more isolation for the same size and lower interwinding capacitance, and it is usually cheaper at low volume.
Can you design the planar winding board for us?
Yes. We can deliver the winding layout as part of your main PCB, or as a separate winding board that we produce and assemble.
Do you build high power planar transformers?
Yes. Above the current a reasonable copper weight can carry, we move the windings to stamped copper.

Start here

Send us your planar spec.

Topology, switching frequency, power, isolation and the height you have. If you are still deciding between planar and wound, send the requirement and we will tell you which one your design wants.

Send us your spec