Two Comparison-Alternative High Temperature PCB-Embedded Transformer Designs for a 2 W Gate Driver Power Supply
Fast power semiconductor devices based on GaN and SiC are becoming more common increasing the need for improved driving circuits. Transformers with smaller inter-winding capacitance in the isolated gate drive power supply help to reduce the conducted EMI emission from the power converter to auxiliary sources. This paper presents a transformer with a small volume, a low power loss and a small inter-capacitance in a gate drive power supply for fast switching devices, such as GaN HEMT and SiC MOSFET. The transformer core is embedded into the PCB to increase the integration density.
Two different transformer designs, the coplanar-winding PCB embedded transformer and the toroidal PCB embedded transformer, are presented and compared, as shown in Fig. 1 and Fig. 2 respectively. Both designs are dedicated to a 2 W gate drive power supply for wide-band-gap device, which can operate at 200°C ambient temperature. The former uses a 'C I' core and PCB winding within the core, which enables a far distance between the primary and secondary windings. Thanks to this structure, the co-planar transformer achieves 0.8 pF inter-capacitance. With the switching device located on the transformer surface, the final converter with 1 MHz switching frequency has a 74% overall efficiency at 2 W output power and its volume is 23 mm x 18 mm x 2.8 mm.
The secondary transformer is called the toroidal PCB-embedded transformer, where the core is toroidal and its windings are twisted around the core. With an optimization on the core size and winding size parameters, a targeted small inter-capacitance, a small transformer loss, and a small total volume, the transformer has a 1.6 pF inter-capacitance allowing the corresponding converter to achieve an 85% efficiency with a 1 MHz switching frequency and a total converter volume of 13 mm x 13 mm x 2.4 mm. The corresponding power density is 72.6 W/in3.