A 98.4% Efficiency 380V-12V DCX With 1.3kW/in3 Power Density Using Low NFoM Devices and Resonant Drive Transformer

The MHz series resonant converter (SRC) dc transformer (dcX) is attractive for its good soft-switching characteristics, which is suitable for high efficiency high power density applications. For a 380-12 V dcX, it has been proved that using series-connected low voltage devices with low NFoM can reduce the conduction loss of the switches [Wu and Shi (2020)]. However, its large driving loss at megahertz frequency becomes a concern, which restricts the further improvement of the efficiency. Furthermore, numerous drivers are required for the series-connected devices and the power density is deteriorated. To reduce the driving loss and improve the power density, a low-profile multioutput resonant drive transformer is applied to the SRC dcX in this article. However, without a well-designed drive speed, the dead time provided will be inappropriate, leading to increased losses or even loss of ZVS in SRC. By properly designing the parameters of the drive circuit, ZVS can be both achieved for the SRC and the drive circuit, diving loss and footprint are reduced significantly and symmetry drive voltages can be achieved. A 380-12V/170A 1 MHz dcX prototype with the reduced power magnetics and the proposed resonant drive transformer is built up, which achieves 98.4% peak efficiency and 1.3 kW/in 3 power density.