Insulated Gate Bipolar Transistor (IGBT), Advantages & Disadvantages

IGBT (Insulated Gate Bipolar Transistor)

We can see that the insulated gate bipolar transistor is a three terminal, trans-conductance device that combines an insulated gate N-channel MOSFET input with a PNP bipolar transistor output connected in a type of Darlington configuration.

As a result the terminals are labeled as: Collector, Emitter and Gate. Two of its terminals (C-E) are associated with the conductance path which passes current, while its third terminal (G) controls the device.

The amount of amplification achieved by the insulated gate bipolar transistor is a ratio between its output signal and its input signal. For a conventional bipolar junction transistor, (BJT) the amount of gain is approximately equal to the ratio of the output current to the input current, called Beta.

The Insulated Gate Bipolar Transistor can be used in small signal amplifier circuits in much the same way as the BJT or MOSFET type transistors. But as the IGBT combines the low conduction loss of a BJT with the high switching speed of a power MOSFET an optimal solid state switch exists which is ideal for use in power electronics applications.

Also, the IGBT has a much lower “on-state” resistance, R_ON than an equivalent MOSFET. This means that the I²R drop across the bipolar output structure for a given switching current is much lower. The forward blocking operation of the IGBT transistor is identical to a power MOSFET.

When used as static controlled switch, the insulated gate bipolar transistor has voltage and current ratings similar to that of the bipolar transistor. However, the presence of an isolated gate in an IGBT makes it a lot simpler to drive than the BJT as much less drive power is needed.

An insulated gate bipolar transistor is simply turned “ON” or “OFF” by activating and deactivating its Gate terminal. Applying a positive input voltage signal across the Gate and the Emitter will keep the device in its “ON” state, while making the input gate signal zero or slightly negative will cause it to turn “OFF” in much the same way as a bipolar transistor or eMOSFET. Another advantage of the IGBT is that it has a much lower on-state channel resistance than a standard MOSFET.

Advantages and Disadvantages of IGBT

Advantages of IGBT are showing below

• Lower gate drive requirements
• Low switching losses
• High input impedance
• Voltage controlled device
• Temperature coefficient of ON state resistance is positive and less than PMOSFET, hence less On-state voltage drop and power loss.
• Enhanced conduction due to bipolar nature
• Better Safe Operating Area

Disadvantages of IGBT are showing below

• Cost
• High turn off time compared to PMOSFET

Device Characteristic	Power Bipolar	Power MOSFET	IGBT
Voltage Rating	High <1kV	High <1kV	Very High >1kV
Current Rating	High <500A	Low <200A	High >500A
Input Drive	Current, hFE 20-200	Voltage, VGS 3-10V	Voltage, VGE 4-8V
Input Impedance	Low	High	High
Output Impedance	Low	Medium	Low
Switching Speed	Slow (uS)	Fast (nS)	Medium
Cost	Low	Medium	High