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BASiC: Negative Gate Turn-Off for SiC MOSFETs Depends on Topology

A Basic Semiconductor analysis says negative gate turn-off is needed mainly in bridge stages, while flyback, forward, Buck and Boost PFC can run 0V turn-off.

Sep 16, 2026 · Dangel Technology editorial

Basic Semiconductor has published a technical analysis of negative gate turn-off in SiC MOSFET drive design. Its conclusion is that whether a negative rail is required depends on the power-stage topology, not on the device alone.

SiC MOSFETs switch far faster than silicon devices, with drain-source dv/dt reaching 50 to 100 V/ns. In a half bridge, a high-side turn-on forces a fast VDS change across the low-side device, and displacement current through its gate-drain capacitance, or Miller capacitance, is injected into the gate. The transient VGS spike can push an off-state MOSFET above its threshold, typically 2.7V to 4V for SiC, risking a shoot-through path.

Miller crosstalk therefore needs three conditions: high dv/dt, a Cgd coupling path and an off-state complementary switch. Flyback, single-switch forward and Buck converters have only one main switch, so no cross-device path exists and 0V turn-off is workable, at the cost of slower turn-off and some extra turn-off loss.

The PFC stages are treated separately: a conventional Boost PFC is a single-switch boost stage that can use 0V turn-off, while a totem-pole PFC runs two MOSFETs in its high-frequency leg and should be evaluated for negative bias. Dual-switch forward and flyback topologies switch their two devices together rather than as a complementary pair, so they avoid the bridge crosstalk path as well.

Dropping the negative rail simplifies the driver and reduces external parts, PCB area and BOM cost, which suits cost- and space-sensitive adapters. Where efficiency or thermal margin dominates, negative turn-off remains an option even in single-switch designs, and newer trench-gate SiC devices with higher threshold voltage and lower Crss are improving device-level immunity.

Industry news compiled by Dangel Technology editorial from public reporting by Chongdiantou (charging industry media). Technical figures are reproduced as reported; verify specifications against the original source before design or procurement decisions.