Flyback Q: Need for a Diode w/ Motor & IGBT?

[mdjensen22]

If I have a circuit driving a motor - say 7A @ 220V through an IGBT that has the anti-parallel C-E diode internal to the part, is there need in putting a flyback diode across the motor still?

 

[DragonPetter]

I do just to be safe. I would guess that IGBT internal body diodes are tough considering the applications of IGBTs, but that's only a guess. The concern you should have is if the body diode is fast enough such that when its reversed biased it doesn't conduct and waste energy. I use fast recovery diodes for flybacks because its simple to do.

 

[mdjensen22]

The body diode is marked as 'ultrafast' with a Trr of 31nS. That's why I'm not sure what the best course of action is (cost vs. benefit). Yay consumer products...

If I understand correctly, the flyback across the motor would force the load to dissipate its own energy to protect the IGBT while the C-E body diode allows the inductive current to flow past the IGBT without the destroying it. Correct?

 

[DragonPetter]

its to protect against a high voltage condition. The inductive spike happens when the switch turns on/off and the large di/dt creates a voltage spike that can blow transistors. The body diode or flyback will let the current keep flowing, hence a lower di/dt and reduces the voltage spike.

 

[alphysicist]

Yes, it is still necessary to include a flyback diode in this circuit. While the IGBT may have an anti-parallel diode built in, it is typically designed for fast switching and may not have the capability to handle the full flyback current from the motor. This could lead to damage or failure of the IGBT. Additionally, the flyback diode can provide a path for the inductive kickback energy from the motor, preventing voltage spikes and protecting other components in the circuit. It is always recommended to include a flyback diode when driving inductive loads such as motors.