Page 114 - Rashid, Power Electronics Handbook

7

Insulated Gate Bipolar

Transistor

S. Abedinpour 7.1 Introduction........................................................................................ 101
Department of Electrical 7.2 Basic Structure and Operation................................................................ 102
Engineering and Computer
Science 7.3 Static Characteristics............................................................................. 103
University of Illinois at 7.4 Dynamic Switching Characteristics.......................................................... 105
Chicago, Illinois 6067 USA 7.4.1 Turn-on Characteristics 7.4.2 Turn-off Characteristics 7.4.3 Latch-up of Parasitic
Thyristor
K. Shenai
851 South Morgan Street 7.5 IGBT Performance Parameters................................................................ 106
(M/C 154) 7.6 Gate-Drive Requirements....................................................................... 107
Chicago, Illinois 60607-7053 7.6.1 Conventional Gate Drives 7.6.2 New Gate-Drive Circuits 7.6.3 Protection
USA 7.7 Circuit Models..................................................................................... 109
7.7.1 Input and Output Characteristics 7.7.2 Implementing the IGBT Model
into a Circuit Simulator
7.8 Applications ........................................................................................ 114
References ........................................................................................... 115

7.1 Introduction period and hence have simple gate-drive requirements. Power
MOSFETs are majority carrier devices, which exhibit very high
switching speeds. However, the unipolar nature of the power
The insulated gate bipolar transistor (IGBT), which was MOSFETs causes inferior conduction characteristics as the
introduced in the early 1980s, has become a successful voltage rating is increased above 200 V. Therefore, their on-
device because of its superior characteristics. The IGBT is a state resistance increases with increasing breakdown voltage.
three-terminal power semiconductor switch used to control Furthermore, as the voltage rating increases, the inherent body
electrical energy and many new applications would not be diode shows inferior reverse recovery characteristics, which
economically feasible without IGBTs. Prior to the advent of leads to higher switching losses.
the IGBT, power bipolar junction transistors (BJTs) and power In order to improve the power device performance it is
metal oxide ®eld effect transistors (MOSFETs) were widely advantageous to have the low on-state resistance of power BJTs
used in low to medium power and high-frequency applica- with an insulated gate input similar to that of a power
tions, where the speed of gate turn-off thyristors was not MOSFET. The Darlington con®guration of the two devices
adequate. Power BJTs have good on-state characteristics but shown in Fig. 7.1 has superior characteristics as compared to
long switching times especially at turn-off. They are current- the two discrete devices. This hybrid device could be gated in
controlled devices with small current gain because of high- the same way as a power MOSFET with low on-state resistance
level injection effects and wide basewidth required to prevent because most of the output current is handled by the BJT.
reach-through breakdown for high blocking voltage capability. Because of the low current gain of BJT, a MOSFETof equal size
Therefore, they require complex base-drive circuits to provide is required as a driver. A more powerful approach to obtain
the base current during on-state, which increases the power the maximum bene®ts of the MOS gate control and bipolar
loss in the control electrode. current conduction is to integrate the physics of MOSFET and
On the other hand, power MOSFETs are voltage-controlled BJT within the same semiconductor region. This concept gave
devices, which require very small current during the switching rise to the commercially available IGBTs with superior on-state

101
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