Bootstrap Drive For SIC MOSFET

MinC

Hi Wolfspeed

Do you have a reference schematic using bootstrap drive for SIC MOSFET in EV HVAC pr Totem pole PFC? Independent power supply with insualted gate driver are recommended , however it is too complicated and high cost compare to traditional Si MOSFET.

Thanks

AAnders

Thank you for your question. We do not currently have a reference design for a bootstrap gate drive circuit. A bootstrap gate drive is an option, but there are several important factors to consider in the design. The overall design is similar to a bootstrap supply for a silicon device, but due to the higher dv/dt and di/dt in a Silicon Carbide system, some additional considerations need to be made.

-The midpoint of a half-bridge circuit will undershoot the negative bus and can lead to increased voltage in the bootstrap circuit. This is due to the forward voltage drop of the body diode as well as parasitic inductance and resistance in the power loop. This effect will increase the voltage on the bootstrap capacitor.

-The parasitic inductance of the bootstrap loop and the junction capacitance of the bootstrap diode can lead to ringing and increase the voltage on the bootstrap capacitor. A diode with low junction capacitance is required to reduce this effect. Additionally, an appropriately sized current limiting resistor can help reduce current peaks and oscillation in the circuit.

The design must ensure that the gate drive voltage remains within the recommended range for the SiC MOSFET according to the datasheet under all operating conditions including start-up. Vgs may need to be clamped to protect the gate from overvoltage during startup.

MinC

Hi Sirs

thanks for you kindly feedback. it would be nice to have reference gate drive schematic if we think it is a option with bootstrap supply which minize the complexity of SIC Gate Driver design.

Thanks

AAnders

Below is a simplified schematic of a bootstrap gate drive for the upper device in a phase leg. The Zener diode (ZD1)in parallel with the capacitor (C1) acts to develop a bipolar gate drive signal to provide additional margin to the gate threshold voltage as recommended in a hard-switched half-bridge application. A 3.3V Zener diode is recommended for C3M SiC MOSFETs, and a 5.1V is recommended for C2M devices.