9020 Datasheet, PDF (7/25 Pages) Fairchild Semiconductor – IGBT Basic II

a. Minimum/maximum rating
The maximum value of V_GG+ is determined by the isolation limit of the gate oxide. If a voltage
exceeding the maximum rated voltage between the gate and the emitter, then the gate oxide
would be destroyed and become useless. As such, the absolute value of V_GG+ in application
must be smaller than the maximum value. The minimum value of V_GG+ is the lowest value
within the limits of saturation during conduction.
b. Effect on state
For the same value of I_C, V_CE(sat) is inversely related to the value of V_GG+. The smaller the
V_GG+, the thinner the channel between n+ layer and n-drift layer becomes, and the resistance
in the channel increases. Due to the conductivity modulation effect not found in MOSFET, volt-
age drop in the n-drift region is significantly smaller than in MOSFET. As such, the portion of
resistance in the channel increases in the voltage drop between the collector and the emitter
during on-state. Considering the aforementioned factors, V_GE decreases during IGBT switch-
ing, and the channel becomes thinner to increase resistance. This leads to an increase in
V_CE(sat), and on-state loss becomes greater. As such, it would be better to use the largest pos-
sible value of V_GG+ from the respect of on-state loss. In applications where on-state loss takes
a large portion, it is important to increase the value of V_GG+, lowering V_CE(sat) in order to
reduce conduction loss. For more detailed values, refer to the transfer characteristics curve in
the data sheet. (Example: Fig. 4)
140 ^{Common Emitter}
T_C = 25℃
20V 15V
120
12V
100
80
60
V_GE = 10V
40
20
0
0
2
4
6
8
Collector - Emitter Voltage, V_CE [V]
Fig. 4. Fairchild SGL50N60RUFD Typical Output Characteristics
c. Effects on turn-on
As V_GG+, (V_GG+ – V_GE(th)) increases, switching time decreases and switching loss becomes
smaller. Greater the I_G flowing into the gate during turn-on, the quicker it charges C_ge, and
V_GE increases rapidly, which leads to a quicker increase in I_C. As seen in the following equa-
tion, I_G increases as V_GG+ increases, and it leads to an increase in di_C/dt.
I_G = (V_GG+ – V_GE) ⁄ R_G
7
Rev. A, April 2002