Gate Drive Circuit of an IGBT
Gate Drive Circuit of an IGBT:
The gate drive circuit of an IGBT should ensure fast and reliable switching of the device. In particular, it should:
- Apply maximum permissible VgE during ON period.
- Apply a negative voltage during off period.
- Control dic/dt during turn ON and turn off to avoid excessive Electromagnetic interference (EMI).
- Control dVCE/dt during switching to avoid IGBT latch up.
- Minimize switching loss.
- Provide protection against short circuit fault.
- The logic level gate drive signal is first opto-isolated and fed to a level shifting comparator. This stage converts the unipolar (usually positive) output voltage of the opto-isolator to a bipolar (±Vgg) signal compatible to the IGBT gate drive levels.
- The output of the comparator feeds a totem pole output amplifier stage which drives the IGBT. The equivalent circuits of the gate drive during turn on and off.
- If |VCC|>|Vgg|then both Q1 and Q2 will operate in the active region and reasonably constant value of β1 & β2 of these two transistors can be used for analysis purpose.
- These equivalent circuits along with the model of the IGBT input MOSFET can be used to analyze the switching performance of the device. Conversely, for a desired switching performance a suitable gate drive circuit can be designed.