Capacitive Power Transfer as Scalable Low-Cost Multi-Load Auxiliary Power Supply for Gate Drivers

Using operating frequencies in the RF range around the 13.56 MHz ISM band, Capacitive Power Transfer (CPT) can provide sufficient power for a wide range of applications even across coupling capacitances of only a few pF. A low power, multi-load power supply can be realized with simple inductorless capacitive links and rectifiers. Multiple loads connect in parallel to a common primary transmission line, driven by a resonant inverter. This scalable low-cost isolating converter can be used in power electronic converters and inverters to simultaneously supply multiple gate drivers with auxiliary power. However, this application presents some unique challenges – in particular, the extremely low coupling capacitances required to limit common-mode interference – which are investigated in this article. It is shown that gate drivers for GaN eHEMTs can be supplied with 35 mW at 5 V using an effective capacitance of only 0.7 pF, and SiC-MOSFETs and even Si-IGBTs can be driven at frequencies in the 10-100's kHz range. Burst tests confirm common-mode immunity even under voltage slopes exceeding 400 V/ns between loads and to ground.