Feature: Power
GaN transistors in AC-DC converters supplying loads up to 100W
R at best.
By David Woodcock, Manager, Power Systems Centre of Excellence, Future Electronics Indeed, the use of GaN HEMTs provides
ecently, there’s been a flurry of new low-cost, compact USB Type-C chargers released on the market, taking advantage of the higher power capability
– up to 100W – of the USB Power Delivery specifications supported by the USB Type-C protocol. Tese new products perform faster charging than earlier USB chargers, housed in a smaller enclosure – a valuable benefit, especially for users of mobile computing devices. Power density of these new products is
impressive: 60W USB Type-C chargers with a power density of 20W/in3
are available at a
price of just €25. Previously at this price point, the power density of USB chargers was 10W/in3
Te new technology underpinning the
high power density of these new chargers is the Gallium Nitride (GaN) power transistor. In the new chargers, the traditional silicon MOSFET power switch is replaced by a GaN High Electron Mobility Transistor (HEMT). Tis is proof that GaN power switch technology has advanced so much, in both performance and cost, that it is replacing silicon MOSFETs in power systems.
similar benefits for industrial, telecoms, medical or military equipment as it does in USB Type-C chargers for the consumer market. Te higher power efficiency achieved with a GaN HEMT allows the power-systems designer to shrink the AC-DC power stage: since less waste heat is generated, there is less need for heat-sinking or for a copper pad on the PCB for heat dissipation. Tis saves cost as well as space. In addition, the lower switching loss in GaN HEMT-enabled power systems gives the option to raise the switching frequency, also reducing the size, weight and cost of the magnetic components.
It should be no surprise, then, that this
technology breakthrough is now sparking great interest among power engineers.
HEMT operation To appreciate the full potential for design optimisation with GaN, it helps first to understand the basic operation of a GaN HEMT. Tis technology is superior to a silicon
power MOSFET because it has some remarkable physical properties. When Aluminium Gallium Nitride (AlGaN) is stacked onto GaN, a spontaneous charge layer is formed at the interface, due to
Figure 1: Cross-section of a GaN HEMT
36 November/December 2020
www.electronicsworld.co.uk
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