6 W Isolated auxiliary power supply for SiC-MOSFET gate driver


Silicon Carbide (SiC) technology is enjoying growing popularity in medium and high voltage power switching applications (typically above 300 V). The extremely fast switching speed of SiC-MOSFETs, their low ON-resistance and excellent thermal performance (conductivity and stability) are some of the key advantages against its Silicon-based counterparts. SiC devices are thus starting to replace IGBT (Insulated Gate Bipolar Transistor) in many applications in industries as diverse as E-mobility, industrial and renewable energy.

The voltage required across the gate-source terminals of a SiC-MOSFET is typically 14 to 20 V for full turn-on and -2 to -5 V for robust turn-off. Note that this negative voltage is required for a faster turn-off transition as well as to keep the device off reliably, preventing spurious Miller-effect turn-on in hard-switched half-bridge applications, due to the very high dv/dt generated across the device terminals during the fast switching transitions. In addition, minimizing the total parasitic capacitance across the isolation barrier is critical for SiC Gate Driver systems in order to achieve higher Common Mode Transient Immunity (CMTI) and better EMI performance. This reference design presents an extremely compact auxiliary power supply, providing two isolated output rails of +15 V and -4 V with a combined total output power of 6 W. With the extremely low interwinding capacitance of the WE-AGDT Transformer down to 6.8 pF, the design is especially optimized for driving Silicon Carbide (SiC) MOSFETs in state-of-the-art applications, and also suitable for IGBT devices.

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