Gate driving requirements of 1 IGBT
1. 1 gate driving voltage
Because of the large gate-emitter impedance of IGBT, it can be driven by MOSFET driving technology, but the input capacitance of IGBT is larger than that of MOSFET, so the driving bias of IGBT should be higher than the bias pressure required for MOSFET driving. Figure 1 is a typical example. At +20℃, the measured threshold of IGBT turn-on voltage below 60 A and 1200 V is 5 ~ 6 V. In practical use, in order to obtain the minimum turn-on voltage drop, UGC ≥ (1.5 ~ 3) Uge (th) should be selected. When UGE increases, the collector voltage Uce will decrease and the conduction loss will also increase. However, in the process of load short circuit, Uge will increase, and the collector current Ic will also increase, which will narrow the pulse width that IGBT can withstand short circuit damage. Therefore, the selection of Ugc should not be too large, so that the IGBT can be completely saturated, and at the same time, the short-circuit current and its stress should be limited (in equipment with short-circuit working process, such as using IGBT in motor, +Uge should try to select the minimum value under the condition of meeting the requirements to improve its short-circuit resistance).
1.2 power requirements
For full-bridge or half-bridge circuits, the driving power sources of the upper and lower tubes should be isolated from each other. Because IGBT is a voltage control device, it needs very little driving power, and it is mainly used for charging and discharging internal input capacitors of hundreds to thousands of picofarads, which requires a lot of instantaneous current. In order to turn off the IGBT quickly, the internal resistance of the power supply should be reduced as much as possible, and in order to prevent the du/dt generated when the IGBT is turned off, a turn-off voltage of -5 V should be added to ensure its complete and reliable turn-off (excessive reverse voltage will cause the IGBT gate-emitter reverse breakdown, generally between -2 ~ 10v).
1.3 driving waveform requirements
From the point of view of reducing loss, the rising edge and falling edge of the gate driving voltage pulse should be as steep as possible. The steep gate voltage at the leading edge makes IGBT turn on quickly, and the time to reach saturation is very short, which can reduce the turn-on loss. Similarly, when IGBT is turned off, the steep falling edge can shorten the turn-off time, thus reducing the turn-off loss and heat generation. However, in practical use, it is not advisable to switch too fast when the inductance load is large. Because in this case, the fast turn-on and turn-off of IGBT will produce a peak voltage Ldi/dt with high frequency, large amplitude and narrow pulse width in the circuit, and this peak is difficult to be absorbed. This voltage may cause IGBT or other components to be damaged due to overvoltage breakdown. Therefore, when choosing the rising and falling speed of driving waveform, it should be considered comprehensively according to the withstand voltage ability of components in the circuit and the performance of du/dt absorption circuit.
1.4 driving power requirements
Since the switching process of IGBT needs to consume a certain amount of power, the minimum peak current can be obtained by the following formula:
I GP =△U ge/R G+R G；
Where △ uge =+△uge =+uge+| uge |；; RG is the internal resistance of IGBT; Rg is the gate resistance.
The average power of the driving power supply is:
P AV =C ge △ Uge 2 f，
Where is it? F is the switching frequency; Cge is the gate capacitance.
1.5 gate resistance
In order to change the steepness of the leading edge and trailing edge of the control pulse, prevent oscillation and reduce the voltage spike of the IGBT collector, a suitable resistor Rg should be installed on the IGBT gate string. When Rg increases, the on-time of IGBT is prolonged, and the loss and heat generation are intensified. When Rg decreases, di/dt increases, which may lead to misleading and damage IGBT. The value of Rg should be selected according to the current capacity, rated voltage and switching frequency of IGBT. Usually it is between several Euros and several tens of Euros (it should be adjusted according to the actual situation in specific application). In addition, in order to prevent the IGBT from being damaged when the gate is turned on or damaged, it is suggested to add a resistor Rge between the gates, and the resistance value is about 10 kω.
1.6 grid wiring requirements
Reasonable gate wiring is very helpful to prevent potential vibration, reduce noise interference and protect IGBT from normal operation.
A. When wiring, the parasitic inductance between the driver output stage and lGBT should be minimized (the area surrounded by the drive loop should be minimized);
B) Place the grid driving board or shielding driving circuit correctly to prevent the power supply circuit from coupling with the control circuit;
C auxiliary emitter terminals should be used to connect the drive circuit;
D. When the output of the driving circuit cannot be directly connected with the IGBT gate, twisted-pair connection (2 rpm/cm) should be adopted;
E for gate protection, the clamping element should be as close as possible to the gate emitter.
1.7 isolation problem
Because power IGBT is mostly used in high voltage occasions in power electronic equipment, the driving circuit must be completely isolated from the whole control circuit in potential. The main methods and their advantages and disadvantages are shown in table 1.
Table 1 isolation methods, advantages and disadvantages between driving circuit and control circuit
Optocoupler isolation
Advantages: small size, simple structure, convenient application, unlimited output pulse width, suitable for PWM controller.
disadvantaged
The interference suppression of 1 and * * * modes is not ideal.
2. The response speed is slow, and the application in high frequency is limited.
3. Auxiliary power supplies that need to be isolated from each other
Use pulse transformer for isolation.
Advantages: fast response speed and good suppression effect on * * mode interference.
Disadvantages:
1, the maximum pulse width of signal transmission is limited by the saturation characteristics of the magnetic core, usually less than 50%, and the minimum pulse width is limited by the magnetization current.
2. Due to the influence of liquid leakage and crust, the processing technology is complicated.
2 Introduction of Typical Gate Driving Circuits
2. 1 pulse transformer drive circuit
The pulse transformer drive circuit is shown in Figure 2. The primary driving circuit of pulse transformer is composed of V 1 ~ V4. By controlling the alternating conduction of V 1, V4, V2 and V3, the driving pulse is applied to the primary side of the transformer, and the secondary side is connected to the gate of IGBT5 through resistor R 1. R 1 and R2 prevent the gate of IGBT5 from being disconnected and provide a charging and discharging circuit. The diode connected in parallel with R 1 is an accelerating diode, which is used to improve the switching speed of IGBT5. Zener diodes VS 1 and VS2 are used to limit the voltage applied to the 5 G-E terminal of IGBT and prevent the gate emission voltage from being too high to break through the gate. In general, the grid voltage should not exceed 20 V.
Fig. 2 Pulse transformer drive circuit
2.2 Optocoupler isolation drive circuit
The isolation drive circuit of optocoupler is shown in Figure 3. Because IGBT is a high-speed device, the selected optocoupler must be a high-speed optocoupler with small delay. The square wave signal output by the PWM controller is added to the base of the transistor V 1, which drives the optocoupler to transmit the pulse to the shaping amplifier circuit IC 1, and after being amplified by the IC 1, a pair of transistors consisting of V2 and V3 drive the optocoupler (V2 and V3 should be β >: 100 switch tubes). The output of the transistor drives the IGBT4 through the resistor R 1, R3 is the gate-emitter junction protection resistor, R2 and the regulator VS 1 form a negative bias voltage generation circuit, and VS 1 usually uses the regulator of 1 w/5.1v. The characteristic of this circuit is only1v.
Fig. 3 isolation drive circuit of optocoupler
2.3 Drive circuit composed of drive modules
The application of the completed driving module circuit to drive IGBT can greatly improve the reliability of equipment. At present, the available driver modules are: EXB840 and 84 1 from Fuji, M57962L from Mitsubishi, KA 10 1 and KA 102 from Luomuyuan, and HCPL3 16J from HP. These modules have the functions of over-current soft turn-off, high-speed optical coupling isolation, under-voltage lockout and fault signal output. Because this module has the advantages of perfect protection function, no debugging and high reliability, the application of this module to drive IGBT can shorten the product development cycle and improve the product reliability. EXB840 and M57962 are introduced in many materials. The information of KA 10 1 and KA 102 can be searched from Baidu. Let's briefly introduce HP's HCPL3 16J. A typical circuit is shown in Figure 4.
Fig. 4 is a driving circuit composed of driving modules.
HCPL3 16J can drive 150 A/ 1200 V IGBT, with optocoupler isolation, COMS/TTL class compatibility, overcurrent soft turn-off, maximum switching speed of 500 ns, working voltage of 15 ~ 30v, and under-voltage protection. The output part is a triple compound Darlington tube, which is output by open collector. Adopt standard SOL- 16 surface mount.
The input and output parts of HCPL3 16J are respectively arranged on both sides of the integrated circuit. The control signal generated by PWM circuit is applied to the 1 pin of 3 16j. The input part needs 1 5 V power supply, and the RESET pin is active low. The fault signal output is sent from the sixth pin to the off end of PWM, and the PWM output is turned off in time when overcurrent occurs. The output part is powered by+15 V and -5 V dual power supply, which is used to generate positive and negative pulse output. Pin 14 is the overcurrent detection terminal, and the IGBT collector voltage is detected by diode VDDESAT. When the IGBT is turned on, if the collector voltage exceeds 7 V, it is considered that an overcurrent has occurred. HCPL3 16J slowly turns off the IGBT, and at the same time, pin 6 sends out an overcurrent signal.
3. Conclusion
Through the analysis of the characteristics of IGBT gate drive and the introduction of typical application circuits, we can have a certain understanding of IGBT application. It can be used as a reference for designing IGBT driving circuit.