To turn on the IGBT, a positive voltage is applied between the gate and the emitter. However, this positive voltage must be higher than the threshold voltage. If the voltage between the gate and the emitter is lower than the threshold voltage, the IGBT will be turned off or in the cutoff state.

Due to the transconductance of the IGBT, the collector current (IC) is a function of the gate-to-emitter voltage, and the saturation voltage drop is also controlled by this voltage. That is, the higher the gate-to-emitter voltage, the larger the collector current and the lower the saturation voltage drop. However, the on-state losses are generally controlled by the saturation voltage drop, so a relatively high control voltage is needed to achieve the lowest on-state losses.

It's also important to note that during short circuits, a high gate-to-emitter voltage will lead to a large short-circuit current. Typically, a compromise value is obtained between the on-state losses during normal operation and the maximum short-circuit current during faults. This value is generally around 15V but should not exceed 20V (the maximum value to ensure reliable operation).

Otherwise, during short circuits, dangerously large currents can easily occur. Consideration should be given to the voltage blocking capability of the gate oxide layer.

Negative Voltage Control

When a negative gate voltage is applied, the IGBT will turn off. Similar to positive voltage, the negative voltage should not be less than -20V, with -15V being a typical value in the datasheet. However, in practical applications, cost is as important as performance, and -15V may not be suitable for all situations. In actual applications, the turn-off voltage can be selected from -15V to 0V, but many applications may choose a turn-off voltage of -10V to -5V for reasons such as:

1. Lower required drive power;

2. Available drive ICs, many of which are developed in CMOS and limit the turn-off voltage, for example, the maximum value between positive and negative supply voltages will be 30V;

Therefore, the gate voltage range will be selected as -10V to -5V to save power while generating negative gate voltage and minimizing costs. For example, in some low-cost IGBT drive applications, abandoning negative voltage can simplify the design of drive power supply.

However, using 0V for turn-off may face the problem of parasitic turn-on in some high-power power electronic devices.

Parasitic Turn-On: Refers to the process where the turned-off IGBT turns on again for a short time.

Alright, that's it for this issue. The VBsemi team greatly appreciates your support!