Figure shows the turn on switching characteristics of IGBT. The delay time t_d(on) is the required time to fall the collector-emitter voltage from V_CE to 0.9V_CE where V_CE is the initial collector emitter voltage. The delay time t_d(on) is also the time required for collector current to increase from its initial value to the 10% of the rated collector current (0.1I_C). The rise time t_r is the required time to increase the collector current from the 10% of the rated collector current (0.1I_C) to its rated value (I_C) and the collector-emitter voltage falls from 90% of V_CE (0.9V_CE) to 10% of V_CE (0.1V_CE). The total turn-on time t_on is sum of delay time and rise time and it is expressed as t_on = t_d(on) + t_r.

After turn-on the IGBT, the collector-emitter voltage falls to small value called ON-state voltage drop V_CES where S represents the saturated value.

Figure: Turn-on Switching Characteristics of IGBT

Figure shows the turn-off switching characteristics of IGBT which is somewhat complex, and the bipolar transistor plays an important role to understand the switching characteristics of a IGBT. The total turn-off time t_off consists of delay time td(off) and rise time, initial fall time t_f1 and final fall time t_f2. The total turn-off time t_off can be expressed as t_off = t_d(off) + t_f1 + t_f2.

The delay time t_d(off) is the required time during which the gate-emitter voltage falls from V_GE to the threshold voltage V_GE(th). Since the gate-emitter voltage falls to V_GE(th) during t_d(off), the collector current falls from rated value (I_C) to the 90% of the rated collector current (0.9I_C).

At the end of delay time t_d(off), the collector-emitter voltage starts to rise.

The first fall time t_f1 is the time during which the collector current falls from the 90% of the rated collector current (0.9I_C) to the 20% of the rated collector current (0.2I_C) or time during which the collector emitter voltage rises from V_CES to 10% of V_CE (0.1V_CE).

The final fall time t_f2 is the time during which the collector current falls from the 20% of the rated collector current (0.2I_C) to the 10% of the rated collector current (0.1I_C) or time during which the collector emitter voltage rises from 10% of V_CE (0.1V_CE) to final value of V_CE.

Figure: Turn-off Switching Characteristics of IGBT