What is the column lifting effect?

In IGBT, there is a parasitic thyristor composed of an N-PN+ transistor and a P+N-P transistor as the main switching device. Among them, there is a body short-circuit resistor between the base and emitter of the NPN transistor, and the lateral hole current in the P body region will produce a voltage drop on this resistor, which is equivalent to applying a forward bias to the J3 junction. In the rated collector current range, this bias is too small to turn on the JBOY3. However, once the JBOY3 is turned on, the gate will lose control of the collector current, which will increase the collector current and damage the device due to excessive power consumption. This phenomenon of out-of-control current is called hold-up effect or self-locking effect, just like the mechanism that ordinary thyristors keep conducting even if the trigger signal is cancelled after being triggered.

cause

In addition to too many ic's, when IGBT is off, if the collector power supply voltage is too high, the leakage current of T 1 tube is too high, and the voltage drop on Rbr may be too high, making T2 turn on, resulting in holding effect.

The third situation where the locking effect may occur is that the MOSFET will turn off very quickly during the turn-off process. After the MOSFET is turned off, the reverse bias voltage UBA of the transistor T2 J2 junction in figure 1(b) increases. The faster the MOSFET turns off, the faster the collector current ic drops and UCA = es-r IC rises. The greater the duCA/dt, the higher the J2 junction capacitance current C2. This junction capacitor current flows through Rbr through point A, which may produce a large voltage drop UAE, make T2 conductive, produce a holding effect, and make IGBT turn off out of control.

The reason for the retention effect may be that the collector current is too large (static retention effect) or the duce/dt is too large (dynamic retention effect), and the risk of retention effect will also be aggravated by the increase of temperature. The cluster effect was once one of the main factors that limited the further improvement of IGBT's current production capacity, but after years of efforts, this problem has been greatly improved since the middle and late 1990s, which promoted the improvement of IGBT's scientific research and manufacturing level.

preventive

In order to prevent the latch-up effect in the turn-off process, on the one hand, a capacitor should be connected in parallel between the collector C and the emitter E of IGBT to reduce the duCE/dt in the turn-off process, and at the same time, the resistance RG of the gate drive circuit in Figure 1(b) can be considered to appropriately slow down the turn-off process of MOSFET. This measure is called slow turn-off technology.