Overview
Integrated gate commutated thyristor (IGCT) is a power semiconductor device used to switch current in industrial equipment. It was developed jointly by Mitsubishi and ABB. The basic structure of an IGCT is shown in Figure 2-90. IGCTs are similar to gate turn-off (GTO) thyristors but have multiple parallel gates.
Operation and Advantages
IGCTs can be turned on and off by gate signals. Compared with GTO thyristors, they exhibit lower conduction losses and can withstand higher dV/dt, so a snubber circuit is often unnecessary in many applications.
Because multiple gates are paralleled, the turn-off current can exceed the anode current. This shortens the time required to remove minority carriers and enables faster turn-off. Paralleling the gates also reduces the inductance and resistance between the device and the gate drive circuit. Compared with GTOs, IGCTs have faster turn-off times and can operate at frequencies up to several kilohertz in short intervals.
Types
IGCTs can be manufactured with or without reverse-blocking capability. Providing reverse blocking requires a long, lightly doped drift region, which increases forward voltage drop.
IGCTs that can withstand reverse voltage are called symmetrical IGCTs (S-IGCTs). Their structure and field distribution are similar to those of GTO thyristors, as shown in Figure 2-91. Typically, the reverse and forward blocking voltage ratings of S-IGCTs are the same. Typical applications for S-IGCTs include current-source inverters.
IGCTs that cannot block reverse voltage are called asymmetrical IGCTs (A-IGCTs). They typically have a reverse breakdown voltage of several tens of volts. Because an n-type buffer layer shortens the drift region, their forward voltage drop is lower than that of S-IGCTs. A-IGCTs are used with an external antiparallel freewheeling diode (for example in voltage-source inverters) or in applications without reverse voltage (for example in switching power supplies or DC traction choppers).
Packaging and Variants
If part of the p+ collector is replaced by an n+ region, that portion serves as an antiparallel freewheeling diode with the IGCT. An asymmetrical IGCT manufactured with a freewheeling diode in the same package is called an RC-IGCT; it provides reverse conduction capability.
Applications
IGCTs are mainly used in variable-frequency inverters, for motor drives in industrial drive systems and traction applications.
