Insulated Gate Bipolar Transistor (IGBT) is a third-generation power electronic device. It operates safely and combines the advantages of power transistors (GTRs) and power MOSFETs, featuring easy driving, large peak current capacity, self-turn-off, and high switching frequency (10-40 kHz). It is currently the fastest-growing new generation of power electronic devices. It is widely used in small-size, high-efficiency frequency converters, motor speed controllers, UPS systems, and inverter welding machines. IGBT driving and protection are key technologies in its application. Based on long-term experience using IGBTs and referring to relevant literature, this paper summarizes some issues related to IGBT gate driving, hoping to provide some assistance to IGBT application personnel. 1 IGBT Gate Driving Requirements 1.1 Gate Driving Voltage Because the gate-emitter impedance of IGBTs is large, MOSFET driving technology can be used. However, the input capacitance of IGBTs is larger than that of MOSFETs, so the driving bias voltage of IGBTs should be stronger than that required for MOSFET driving. Figure 1 is a typical example. At +20 ℃, the measured turn-on voltage threshold for IGBTs with a current of 60 A and below 1200 V is 5-6 V. In practical applications, to obtain the minimum conduction voltage drop, Ugc should be selected as ≥ (1.5-3)Uge(th). When Uge increases, the collector-emitter voltage Uce will decrease during conduction, and the turn-on loss will decrease accordingly. However, during a load short circuit, Uge increases, and the collector current Ic will also increase, making the pulse width that the IGBT can withstand for short circuit damage narrower. Therefore, the selection of Ugc should not be too large, which is sufficient to fully saturate the IGBT and also limits the short circuit current and the stress it brings. (In equipment with short-circuit operation, such as when using IGBTs in motors, +Uge should be selected as low as possible while meeting the requirements to improve its short-circuit withstand capability.) 1.2 Power Supply Requirements: For full-bridge or half-bridge circuits, the drive power supplies for the upper and lower transistors must be isolated from each other. Since IGBTs are voltage-controlled devices, the required drive power is very small, mainly for charging and discharging their internal input capacitors of several hundred to several thousand picofarads. A large instantaneous current is required to ensure rapid IGBT turn-off. The internal resistance of the power supply should be minimized. Furthermore, to prevent the du/dt generated during IGBT turn-off from mistakenly turning the IGBT on again, a -5V gate-off voltage should be applied to ensure reliable turn-off (excessive reverse voltage will cause reverse breakdown of the IGBT gate emitter; generally, it should be between -2V and 10V). 1.3 Drive Waveform Requirements: From the perspective of reducing losses, the rising and falling edges of the gate drive voltage pulse should be as steep as possible. A very steep leading edge of the gate voltage allows the IGBT to turn on quickly, reaching saturation in a very short time, thus reducing turn-on losses. Similarly, a steep falling edge shortens the turn-off time when the IGBT turns off, thereby reducing turn-off losses and heat generation. However, in practical applications, excessively fast turn-on and turn-off are actually detrimental under large inductive loads. This is because, under such conditions, excessively fast IGBT turn-on and turn-off will generate high-frequency, large-amplitude, and narrow-pulse-width spike voltages Ldi/dt in the circuit, and these spikes are difficult to absorb. This voltage may cause the IGBT or other components to be damaged by overvoltage breakdown. Therefore, when selecting the rise and fall speeds of the drive waveform, the voltage withstand capability of the components in the circuit and the performance of the du/dt absorption circuit should be considered comprehensively. 1.4 Requirements for Drive Power Since the switching process of the IGBT requires a certain amount of power, the minimum peak current can be calculated by the following formula: IGP = ΔUge/RG + Rg; where ΔUge = +Uge + |Uge|; RG is the internal resistance of the IGBT; Rg is the gate resistance. The average power of the drive power supply is: PAV = Cge / ΔUge / 2f, where... f is the switching frequency; Cge is the gate capacitance. 1.5 Gate Resistance: To change the steepness of the control pulse's leading and trailing edges and prevent oscillation, reducing the voltage spike at the IGBT collector, a suitable resistor Rg should be connected in series with the IGBT gate. When Rg increases, the IGBT conduction time prolongs, and losses and heat generation intensify; when Rg decreases, di/dt increases, which may cause false turn-on and damage the IGBT. The value of Rg should be selected according to the IGBT's current capacity, voltage rating, and switching frequency. It is usually between a few ohms and tens of ohms (in specific applications, it should be adjusted appropriately according to the actual situation). In addition, to prevent damage to the IGBT from the main circuit when the gate is open or damaged, it is recommended to add a resistor Rge between the gate and emitter, with a resistance of about 10 kΩ. 1.6 Gate Wiring Requirements: Reasonable gate wiring is very helpful in preventing potential oscillations, reducing noise interference, and protecting the normal operation of the IGBT. a. When wiring, the parasitic inductance between the driver's output stage and the IGBT must be minimized (the area enclosed by the drive circuit should be minimized); b. The gate driver board should be correctly placed or the drive circuit should be shielded to prevent coupling between the power circuit and the control circuit; c. An auxiliary emitter terminal should be used to connect the drive circuit; d. When the drive circuit output cannot be directly connected to the IGBT gate, a twisted pair cable (2 turns/cm) should be used; e. Gate protection and clamping elements should be placed as close as possible to the gate emitter. 1.7 Isolation Issues Since power IGBTs are mostly used in high-voltage applications in power electronic equipment, the drive circuit must be completely isolated from the entire control circuit in terms of potential. The main approaches and their advantages and disadvantages are shown in Table 1. 2. Typical Gate Drive Circuit Introduction 2.1 Pulse Transformer Drive Circuit The pulse transformer drive circuit is shown in Figure 2. V1 to V4 form the primary side drive circuit of the pulse transformer. By controlling the alternating conduction of V1, V4, V2, and V3, the drive pulse is applied to the primary side of the transformer. The secondary side is connected to the gate of IGBT5 through resistor R1. R1 and R2 prevent the IGBT5 gate from opening and provide a charging and discharging circuit. The diode connected in parallel on R1 is an accelerating diode, used to improve the switching speed of IGBT5. The function of the Zener diodes VS1 and VS2 is to limit the voltage applied to the g-e terminal of IGBT5 to avoid excessive gate-emitter voltage breakdown of the gate. The gate-emitter voltage should generally not exceed 20V. Figure 2 Pulse Transformer Drive Circuit 2.2 Optocoupler Isolation Drive Circuit The optocoupler isolation drive circuit is shown in Figure 3. Since IGBTs are high-speed devices, the selected optocoupler must be a high-speed type with small delay. The square wave signal output by the PWM controller is applied to the base of transistor V1. V1 drives the optocoupler to transmit the pulse to the shaping and amplifying circuit IC1. After being amplified by IC1, it drives the transistor pair composed of V2 and V3 (V2 and V3 should be switching transistors with β > 100). The output of the transistor pair drives IGBT4 through resistor R1. R3 is a gate-emitter junction protection resistor. R2 and Zener diode VS1 form a negative bias voltage generation circuit. VS1 is usually a 1 W/5.1 V Zener diode. The characteristic of this circuit is that it can output positive and negative drive pulses with only one power supply, making the circuit relatively simple. Figure 3 Optocoupler Isolation Driver Circuit 2.3 Driver Circuit Composed of Driver Modules Using ready-made driver module circuits to drive IGBTs can greatly improve the reliability of the equipment. Currently, the main driver modules available on the market include: Fuji's EXB840 and 841, Mitsubishi's M57962L, Luomuyuan's KA101 and KA102, and HP's HCPL316J and 3120, etc. These modules all have overcurrent soft shutdown, high-speed optocoupler isolation, undervoltage lockout, and fault signal output functions. Because these modules have the advantages of comprehensive protection functions, no debugging required, and high reliability, using these modules to drive IGBTs can shorten the product development cycle and improve product reliability. There are many materials introducing EXB840 and M57962. Materials for KA101 and KA102 can be found on the website http://www.pwrdriver.com/product/ka101.php. Here, we will briefly introduce HP's HCPL316J. A typical circuit is shown in Figure 4. Figure 4 shows the driver circuit of the HCPL316J, which can drive 150 A/1200 V IGBTs. It features optocoupler isolation, CMOS/TTL level compatibility, overcurrent soft shutdown, a maximum switching speed of 500 ns, an operating voltage of 15–30 V, and undervoltage protection. The output section uses a triple-combined Darlington transistor with open collector output. It is mounted on a standard SOL-16 surface mount. The input and output sections of the HCPL316J are arranged on opposite sides of the integrated circuit. The control signal generated by the PWM circuit is applied to pin 1 of the 316J. The input section requires a 5 V power supply. The RESET pin is active low. The fault signal output is sent from pin 6 to the PWM shutdown terminal, promptly shutting down the PWM output in case of overcurrent. The output section uses a dual power supply of +15V and -5V to generate positive and negative pulse outputs. Pin 14 is the overcurrent detection terminal, which detects the IGBT collector voltage through diode VDDESAT. When the IGBT is turned on, if the collector voltage exceeds 7V, an overcurrent phenomenon is considered to have occurred, and the HCPL316J slowly turns off the IGBT, while simultaneously sending an overcurrent signal from pin 6. 3. Conclusion Through the analysis of the IGBT gate drive characteristics and the introduction of typical application circuits, readers have gained a certain understanding of IGBT applications. This can serve as a reference for designing IGBT drive circuits.