Characteristics of Integrated Gate Bipolar Transistor (IGBT)

IGBTs or integrated gate bipolar transistors to give them their full name are semiconductor components with highly specific uses. They are similar in a way to power transistors but have significant differences in the way they are controlled. Power transistors are controlled by the amount of current flowing across their base in contrast to IGBTs which are controlled by the voltage applied to their gate. The characteristics of the IGBT make them more of a combination of a power transistor and a MOSFET (metal-oxide semiconductor field effect transistor).

The IGBT is most commonly used in applications where high frequency power switching is needed. One of the reasons why the IGBT works well for this purpose is that only a tiny amount of current is needed applied to its gate. The current is only very small because of high impedance at the control gate. IGNTs are not only able to be switched much more rapidly than other types of semiconductor but they also have other desirable characteristics, especially the fact that they can be used at high voltages.

High power, high frequency devices work by turning the current on and off rapidly with the help of a switching device. Apart from IGBTs, other switching components include MOSFETS and bipolar transistors. An oscillating device is used to control the IGBT or other type of switch.

One common application of IGBTs is in a high voltage electric motor. The voltage used by the motor is converted from DC to AC with the IGBT controlling the frequency at which the AC is provided. There are three different types of motors which may have IGBTs incorporated into their control device. These are,

A three phase induction type motor

A three phase brushless motor with sinusoidal BEMF

A three phase brushless motor with trapezoidal BEMF

The motor drive may be either of a sinewave or squarewave type. Sinewaves are preferred where RF interference might be a nuisance, although squarewave drives are actually the more efficient of the two. Of the three motor types, the first one, the induction motor tends to have a sinewave type drive, although there are high and low pulses in any wave phase noticeable.

The other two types of motor use magnets instead of rotors that are found in induction motors. These motor types are somewhat more expensive than induction motors, but more efficient. The main difference between the two types of brushless motor is the type of wave produced by their drives: some are trapezoidal, others are sinewave. In all these motors, there are three phases involved and six transistors. MOSFETs tend to be the preferred choice at lower voltages, say 200 volts or less, but for higher voltages, the IGBTs are preferred. IGBTs can handle voltages of up to 1200 volts.