Gate drive circuit of IGBT

Gate drive circuit of IGBT

IGBT is a composite structure in which GTR is the leading element and MOSFET is the driving element, so the gate drive circuit used for power MOSFET is also applicable to IGBT in principle. IGBT is a voltage-driven device. The static gate input impedance is high, but the gate has capacitance. The main task of IGBT driving is to charge and discharge the gate input capacitance.

1. IGBT’s requirements for the drive circuit

(1) The gate drive voltage pulse should have steep enough rising and falling edges. Thus, the IGBT is turned on and off quickly, reducing switching time and switching losses.

(2) The peak voltage of IGBT gate-emitter is up to ±20~±30V, and the driving voltage is generally 15V; a negative drive voltage of a certain magnitude needs to be applied during turn-off, generally -15~-2V, so as to improve the reliability of turn-off and prevent false turn-on.

(3) IGBT is a voltage-type driving device, and the driving power is very small compared to GTR, which is mainly used to charge the gate capacitance. The drive power is proportional to the amount of gate charge, the absolute value of the gate drive voltage (the absolute value of the difference between positive and negative drive voltages), and the operating frequency.

(4) The drive current required by the IGBT is determined by the gate resistance in the designed drive loop.

(5) After the IGBT is turned on, the driving circuit must maintain enough driving power so that the IGBT will not exit saturation and be damaged.

In addition to the above basic functions, the integrated drive circuit generally has the following functions:

(1) It has Desat protection, that is, it detects the saturation voltage drop when it is turned on. If the device exits saturation, it is considered that a short circuit occurs, and the device needs to be turned off within a specified time.

(2) With soft-off function. In the event of a short circuit in the circuit, the IGBT should be turned off. To reduce the higher dic/dt at turn-off and reduce the voltage UCE overshoot at turn-off, a soft turn-off function must be used.

(3) Low-voltage protection of the power supply voltage, if the driving voltage is lower than a certain value (such as below 12V), it may enter a desaturated state, and the conduction loss increases sharply. The driver needs to detect the power supply voltage, and it is forbidden to drive when the low voltage is protected.

Compared with the discrete component drive circuit, the integrated module drive circuit has strong anti-interference ability, fast working speed and perfect protection function, which can realize the optimal drive of IGBT. Commonly used are Fuji’s EXB series, Mitsubishi’s M579 series and Siemens’ 2ED020112, etc.

2. Example of IGBT drive circuit

Figure 1 is a functional block diagram of the high-speed EXB841 integrated drive circuit, whose maximum switching frequency is 40kHz. The structure of EXB841 can be divided into 3 parts: amplification, overcurrent protection and 5V reference voltage. Figure 2 shows the actual application circuit of EXB841, where V is the driven IGBT.

Gate drive circuit of IGBT
Figure 1-EXB841 functional block diagram
Gate drive circuit of IGBT
Figure 2 – EXB841 practical application circuit

For high-power power electronic devices, we generally choose the dedicated driver module specially provided by the device manufacturer for the device to achieve good performance matching. (Extended reading: The structure and working principle of IGBT, the basic characteristics and main parameters of IGBT.)