The most critical moment in the gate drive is the IGBT opening and closing. Our goal is to perform this function quickly with minimal noise and ringing when the IGBT is on. However, too fast a rise/fall time can lead to unnecessary ringing and poor EMI, and too slow a rise/fall time can increase the switching loss of the IGBT.
The picture above shows DGD0216 gate driver assembly from Diodes. With careful selection of RG and RRG, the rise and fall times of IGBT gate drivers can be selectively controlled. When turned on, all current will flow through the IC through the RG and charge the IGBT gate capacitor, so increasing or decreasing the RG will correspondingly increase or decrease the rise time in the application. With the addition of the DRG, the down time can be controlled independently because the off current flows from the IGBT gate capacitor through the RRG and the DRG to the driver in the integrated circuit to GND. Therefore, increasing or decreasing the RRG will correspondingly increase or decrease the fall time. Sometimes this fine control is not needed, in which case you can just use RG.
Increasing on and off limits the ringing and noise caused by parasitic inductors, so in noisy environments, it may be necessary to increase the gate resistance. The choice of gate element is a compromise, that is, on the one hand, the faster the rise time, the more ringing, the worse the electromagnetic interference, but the higher the efficiency; On the other hand, the slower the rise time, the better the electromagnetic interference and noise performance, and the worse the efficiency.
The exact value of the gate element depends on the application's parameters and system requirements. RG values are usually between 5Ω and 50Ω, with the optimal value determined by the IGBT gate capacitance and the drive current of the gate driver. RRG values are usually between 3 and 20Ω, with the optimal value determined by the IGBT gate capacitance and the drive current of the gate driver.
