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INDUSTRIAL CONTROL HANDBOOK - 3.5 INSULATED GATE BIPOLAR TRANSISTORS

Another transistor-type device is a combination of a metal-oxide semiconductor (MOS) transistor and a bipolar transistor. This device is called an insulated gate bipolar transistor (IGBT). Combining these two devices provides the high-voltage gain feature of the MOS device, and the high-current gain feature of the bipolar transistor. The combination of these two devices also provides better speed characteristics.

The MOS part of the device provides low on-state losses, which make it easier to control at higher voltages. The device also exhibits switching speeds up to 20 kHz. Fig. 3-21 shows the electronic symbol for the devices. The IGBT is used in circuit applications up to 1000 volts.

FIGURE 3-21 Electronic symbol and typical package for the insulated gate bipolar transistor (IGBT).FIGURE 3-21 Electronic symbol and typical package for the insulated gate bipolar transistor (IGBT). (Courtesy of Harris Semiconductors.)

FIGURE 3-22 Block diagram for a circuit that provides IGTBs to sense current in a dc motor drive circuit. The output signal from the IGBTs is sent to protect circuits in the drive. The IGBTs also provide signals that are used for dc braking.FIGURE 3-22 Block diagram for a circuit that provides IGTBs to sense current in a dc motor drive circuit. The output signal from the IGBTs is sent to protect circuits in the drive. The IGBTs also provide signals that are used for dc braking. (Courtesy of POWEREX Inc.)

Fig. 3-22 shows a typical application for an IGBT. In this application several IGBTs are used in a motor drive circuit to monitor current for the drive. The output from the current-sensing IGBTs is sent to four protection circuits that check for short-circuit faults, exceeding maximum overcurrent, exceeding maximum temperature, and undervoltage (UV). The IGBTs are also used in this application to provide an output signal that can be used to provide dc braking for the motor.

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