Design Considerations for Magnetics in GaN Applications

As the power electronics world starts to invest more into GaN devices, the need for GaN-ready magnetics becomes more imminent. There is no one solution fits all when it comes to designing for GaN, and it would be in the best interest of those seeking GaN-ready magnetics to work with an established supplier of magnetic components with the resources to custom design solutions for their customers.

As GaN technology is suited for faster switching speeds and higher operating temperatures, designers of magnetics need their parts to be rated for higher temperature and to operate at higher frequencies. A versatile magnetics designer will have an arsenal of a variety of specialty core and wire manufacturers under their belt that offer unique materials for higher operating and higher frequency applications over the standard materials offered in the market.

The core would generally need to be comprised of a ferrite alloy suited for minimal losses at a higher frequency and the designer would need to monitor its saturation point in the circuit taking into consideration the higher operating temperature of the GaN application. As with picking any specialty material over a standard material, there are electrical, thermal, chemical and mechanical trade-offs that need to be considered in the overall design when designing for GaN applications. Potential considerations include but are not limited to changing from standard ferrite core materials to using high permeability core materials such as nanocrystalline and amorphous cores. When compared to traditional ferrite cores, nanocrystalline and amorphous cores provide a wider operational temperature and significantly higher impedance. This makes these cores a choice solution for common mode chokes in switched-mode power supplies (SMPS), uninterruptible power supplies (UPS), solar inverters, frequency converter and EMC filter applications.

In respect to windings, skin effect becomes more of a challenge as losses will exponentially increase after entering into the higher switching frequency range. Potential considerations include but are not limited to changing from winding a transformer with standard magnet wire to winding using Litz wire to reduce the overall wire gauge by using multiple, smaller strands. This not only reduces the copper loss from skin effect at higher frequencies but also further disperses the distribution of heat as the current density is shared amongst the multiple strands of wires. Parasitic management also needs to be considered in terms of winding capacitance and leakage inductance. Winding configuration is crucial to both of these electrical parameters that can be controlled by sectioning a bobbin or a optimizing a toroidal winding instead. Another potential consideration in designing for GaN applications is designing the magnetic as an integrated planar transformer, in which case the winding would be embedded into the printed circuit board. In higher-density converter magnetics, PCB-based winding configurations become a practical design output. The use of a PCB for the winding allows for individual windings to be printed on each side, of each layer, of a board, which allows for interleaving without the typical wiring challenges seen in conventional transformers. This reduction in wire thickness and added interleaving combines to reduce leakage and skin effect losses at higher frequencies. Additionally, the greater surface area of the winding helps in distributing the heat more evenly around the core to reduce the overall thermal impact of temperature rise experienced in conventional transformers. These benefits do come at a cost of a lower window of utilization for the windings, an increased footprint area and increased parasitic capacitance.

All-in-all, the specific application will expose the design options and material choices that are available to design in the magnetic. The winding and core options discussed are two of the major variables at play, but there are many additional material variables that need to be considered for the overall integrity of the magnetic to be best suited for its respective application. Ultimately, the responsibility falls on the experience of the magnetic supplier designer to explore all suitable paths to best design a magnetic that will operate at peak efficiency in a higher temperature and higher frequency GaN application.

For further information or to discuss your needs with a design engineer, please contact Vanguard Electronics at info@ve1.com.