Power Electronics Europe Feb/March 2023

20 POWER TRANSISTORS www.epc.co.com Issue 1 2023 Power Electronics Europe www.power-mag.com eGaN FETs enable more than 4 kW/in 3 power density for 48 V to 12 V power conversion Introduction Growing computational power and miniaturization of electronics in computing and datacenters is increasingly putting pressure in 48 V power delivery and conversion systems. High efficiency and high-power density converters enable a reduction in power losses at the system level while allowing smaller form factors. In this context, LLC resonant topologies combined with GaN technology succeed to deliver outstanding performance, as it has been demonstrated with multiple examples [1-4]. This article will show the key design parameters and components to achieve beyond 4 kW/in3 of power density in a 48 V to 12 V LLC converter using eGaN FETs. This work is an evolution of [2] and it was first introduced in [1], demonstrating 96.3% peak efficiency and 93.8% when delivering 1 kW into a 12 V load and with module dimensions of 17.5 x 22.8 x 7.7 mm. Converter Overview The LLC resonant converter presented here features a primary full bridge and a center- tapped full wave synchronous rectifier for the secondary as shown in Fig 1 (left). Both are coupled with a planar transformer having a 4:1 turns ratio. The power FETs used in the primary and secondary, together with the transformer and printed circuit boards are the key components of the module. Figure 1 (right) shows a photo of the overall module assembled Power Transistors and Gate Drivers For the primary circuit, four 100 V rated GaN transistors in Chip Scale Package (CSP) enable higher than 4 kW/in3 power density for 48V to 12V power conversion using an LLC resonant converter with up to 1 kW capability. Alejandro Pozo. ABOVE: Fig. 1 (left) Topology of the LLC converter, (right) photo of the assembled LLC power converter module RIGHT: Fig. 2 (left) top view and dimensions of optimised core (right) full FEA model of the core showing the flux density throughout the core