Hybrid-flyback and GaN enable ultra-high power density 240W USB-PD EPR adaptor

Featuring a step forward towards a universal adaptor the USB-PD 3.1 standard specifies variable output voltages from 5 V to 48 V. This rises new challenges for converter topologies used up to now. In this paper, an active PFC followed by an asymmetrical half-bridge flyback will be proposed for such application, the interaction between both stages for optimum efficiency and stand-by power will be explained. Gallium Nitride (GaN) switches and the asymmetrical half-bridge flyback topology, also well known as hybrid flyback, will be combined in the DC-DC stage to demonstrate the potential. Using GaN HEMTs devices in the half-bridge of the DC-DC power stage and the proper control techniques provides the so-called “flyback effect” which improves efficiency greatly. This effect will be described for the first time in this paper. Its benefit in terms of efficiency over wide output voltage range will be analyzed. Finally, the advantages of the proposed control methods are demonstrated in a 240 W AC-DC prototype. It achieves a full load efficiency of up to 96.84% and an ultra-high-power density of 44 W/inch
³
(uncased) while it is able to deliver an output voltage from 5 V to 48 V with input voltage range from 90 Vac to 265 Vac.