Custom planar transformer

The customer needed a transformer for a Formula-E race car, and the end product's dimensions had already been fixed before the magnetics were designed. The space available for 2kW of power was too small for any conventional magnetic design to fit. Without a solution, the customer would have had to stop development entirely and restart the design from scratch — losing months of work

• Extremely limited space — a maximum footprint of 50 x 34 x 25mm for 2kW of power
• Dimensions fixed in advance — the end product's size was set before the magnetics were designed, leaving no room to adjust the constraints
• High ambient temperature — the transformer had to run at full power (2kW) without overheating at an ambient temperature of +70°C
• High stakes for the customer — falling short meant restarting the entire design process, at the cost of months of development time

We approached the problem through simulation, custom components, and precision manufacturing:

• Full 3D simulation — the entire design was modeled in Ansys 3D simulation software, combined with our own proprietary software routines, to explore the design space before committing to hardware
• Custom-height ferrite cores — based on a standard core shape, adapted in height to make the most of the limited space
• Custom PCB stack-up — using high-performance laminates to reduce spacing between layers, maximizing how much of the ferrite core's window could actually be used for windings
• Laser-cut copper windings — the secondary winding was manufactured from laser-cut copper, with terminal positions custom-matched to the customer's PCB holes

Every part of the design was shaped by the space constraint. Multiple iterations were simulated in Ansys before any hardware was built, then translated into a custom ferrite core height, a high-laminate PCB stack-up, and laser-cut secondary windings matched exactly to the customer's PCB — turning a seemingly impossible design into a working transformer.

• Higher efficiency — the new PCB laminate materials improved copper utilization and overall efficiency
• Better thermal performance — we advised the customer to machine a small pocket into their aluminium baseplate so the transformer's ferrite core could sit within it, allowing the windings to be cooled directly through gap pads to the coldplate
• Lower losses — running multiple design simulations made it possible to optimize the design for the lowest possible losses
• Improved reliability — the high-temperature, high-performance PCB laminates reduce the risk of high-voltage breakdown at the application's high input DC bus voltages
• Very high power density — 800W per cubic inch, resulting in a much smaller footprint than a conventional design
• Tightly controlled leakage inductance and parasitic capacitance, on top of the power density gains