Isolated gate-driver bias supplies are widely used in the traction inverter, on board charger, UPS, and solar inverters. A simple, robust design is required since it is a supporting component of the overall system. The use of wide bandgap devices such as SiC or GaN MOSFET in the inverters, demands higher switching speed. Therefore, it is critical to minimize the EMI noise coupling through the gate-driver bias supply transformers.

The paper discusses the bias supply design considerations, including the system architecture, control method, as well as the EMI and CMTI performances. The open-loop LLC converter is discussed in detail. LLC resonant topology can use an isolation transformer with larger leakage inductance but minimum primary side to secondary side parasitic capacitor. This small parasitic capacitance reduces the common mode noise coupling from the inverter switch node. Besides, due to the soft switching and sinusoidal current, the LLC converter inherently provides less EMI noise. Together with the open loop control, the LLC converter provides a simple, robust, and low-EMI solution for the inverter gate driver bias supplies.