Today, the editor mainly analyzes and expounds the driving application circuit of IGBT. Taking the hybrid integrated circuit EXB841 as an example, it is a typical driving circuit, which can not only drive up to 400A 600V IGBT and up to 300A 1200V IGBT, but also has more complete module functions. , with single power supply, positive and negative bias, overcurrent detection, protection, soft shutdown and other main features.
The drive circuit is powered by +20V DC power supply and can generate +15V open gate voltage and -5V closed gate voltage. It is equipped with TLP550 high-speed optocoupler isolation chip, and the signal delay of the drive circuit is less than 1us. It integrates an overcurrent detection circuit and a low-speed Overcurrent cut-off circuit, so it has been widely used in China. However, pay attention to the following aspects when using this module:
1. The gate-emitter drive circuit wiring of IGBT must be less than 1 m;
2. The gate-emitter drive wiring of IGBT should be twisted pair;
3. If the IGBT collector generates a large voltage pulse, it is necessary to increase the gate series resistance of the IGBT;
4. The 47uF capacitor is used to absorb the voltage change caused by the impedance of the power wiring, not the capacitor of the power filter.
When the IGBT is working normally, pin 5 of the overcurrent signal indication terminal of EXB841 is high level, 4N25 is not conducting, the R pin of the trigger is "0", and the Q pin is "1", that is, the IGBT is working normally. When there is an overcurrent signal in the IGBT, the internal overcurrent detection circuit of EXB841 delays for a few microseconds to filter out the interference signal, pin 5 becomes low level, 4N25 is turned on, the flip-flop is turned over, the Q pin is "0", At the same time, the driving signal of the IGBT is turned off, so as to play a protective role. In the work, the special integrated drive module EXB841 is used to drive the electromagnetic excitation coil of a high-frequency fatigue testing machine with an inductive load of 2 kw, and the effect is remarkable.
To sum up, the following conclusions are drawn from the analysis of IGBT drive and protection by combining with practical applications:
1. Since the gate series resistance and the internal impedance of the driving circuit will have a great influence on the turn-on process of the IGBT and the waveform of the driving pulse, various aspects should be comprehensively considered in the design process.
2. Under large inductive loads, the switching time of the IGBT cannot be too short to limit the peak voltage formed by di/dt, thereby ensuring that the IGBT is not damaged.
3. Since IGBTs are mostly used in high-voltage occasions in power electronic equipment, the driving circuit and the control circuit are strictly isolated in terms of potential, and the connection distance between the driving circuit and the IGBT is shortened.
4. The gate drive circuit of IGBT should be as simple and practical as possible, preferably with its own protection function for IGBT and strong anti-interference ability.
5. In the actual application process, in order to achieve better results, it is necessary to adopt methods such as soft turn-off and drop gate voltage in overcurrent protection; use a clamp circuit to prevent surge voltage, etc.
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