9020 Datasheet, PDF (4/25 Pages) Fairchild Semiconductor – IGBT Basic II

3. IGBT switching waveforms
Switching waveform of the IGBT in a circuit under a clamped inductive load (CIL) is shown in
Fig. 2. This waveform can be applied to both inverter and chopper circuits using inductive
load. This is a real waveform that reflects the effects of diode recovery and stray inductance,
and principles of their operations will be considered by region. Consolidated understanding of
IGBT’s real application switching waveforms and principles of operation is necessary in
designing an IGBT gate drive.
A. Analysis of turn-on transient
V_GE(t)
V_{GE, Io}
V_GE(th)
0
V_GG+
V_GE(t)
V_CE(t), I_C(t)
V_CE
V_CE(t), I_C(t)
V_CE
I_C
I_C
0
t0 t1 t2 t3 t4
V_CE(sat)
t5
0
t6
t7 t8 t9
(a) Turn-on
(b) Turn-off
Fig. 2. IGBT Switching Waveforms
V_GG-
MOSFET current
BJT current
LOAD
Ls
+
Vdc
-
Ls
DUT
Fig. 3. IGBT Switching Test Circuit
The test circuit illustrating the characteristics of IGBT is shown in Fig. 3. In addition, Fig. 2
shows IGBT switching waveforms obtained from the test circuit in Fig. 3. IGBT’s turn-on
switching waveform is very similar to MOSFET switching characteristics, and turn-off switching
characteristics are similar as well except IGBT’s tail current. The following are descriptions of
each region shown in Fig. 2 and their principle of operation.
4
Rev. A, April 2002