Difference between BJT and IGBT

Bipolar Junction Transistor (BJT) and Insulated Gate Bipolar Transistor (IGBT) are two types of transistors that are used in electronic circuits to control the currents. Read through this article to get an overview of how BJTs and IGBTs function and the major differences between them.

What is BJT?

BJT stands for Bipolar Junction Transistor. The BJT is a three layer, three terminal semiconductor device which is used in the electronic circuit for switching and amplification of signals

A BJT is formed by sandwiching either a P-type or N-type material between two layers of N-type material or P-type material respectively. Thus, based on the construction, the BJT is of two types: NPN and PNP. The BJT consists of two PN junctions and the three terminals of a BJT are: emitter (E), base (B) and collector (C).

What is IGBT?

IGBT stands for Insulated Gate Bipolar Transistor. An IGBT is also a three terminal semiconductor device used for switching purposes. The IGBT is a type of transistor that has ability to handle large amount of power and has high switching speed which makes it more efficient than a BJT. The three terminals of the IGBT are: emitter (E), gate (G) and collector (C).

Actually, the IGBT has a combination of features of MOSFET and BJT. Hence, it can handle high currents and high power of the order of kW.

Difference between IGBT and BJT

The following table highlights the major differences between bipolar junction transistor and insulated gate bipolar transistor −

Parameter	BJT	IGBT
Full form	BJT stands for Bipolar Junction Transistor.	IGBT stands for Insulated Gate Bipolar Transistor.
Definition	BJT is a three terminal, three layer semiconductor device used for switching and amplification.	IGBT is also three terminal semiconductor switching device mainly used in power electronic circuits
Terminals	BJT has three terminals named: Emitter (E), Base (B) and Collector (C).	IGBT also has three terminals named: Emitter (E), Collector (C) and Gate (G).
Control quantity	BJT is a current controlled device.	IGBT is a voltage controlled device.
Control terminal	The base terminal has the control on the operation of the BJT.	Gate terminal has control on the operation of the IGBT.
Drive circuit	BJT has a complex drive circuit.	The drive circuit for an IGBT is relatively simple.
Switching speed	The switching speed of the BJT is low.	For IGBT, the switching speed is comparatively high.
Switching time	The switching time for a BJT is of the order of 10 $\mu$s.	For IGBT, the switching time is of the order of 0.5 $\mu$s.
Drive power	BJT requires large drive power.	IGBT require low drive power.
Switching power losses	For BJT, the switching losses are relatively high	In IGBT, the switching losses are less than BJT.
Switching frequency rating	For a BJT, the switching frequency is about 20 kHz.	The switching frequency for an IGBT is about 160 kHz. Which is very high than that of a BJT.
Input impedance	For BJT, the input impedance is low.	The input impedance of IGBT is high than that of BJT.
Safe operating area (S.O.A.)	BJT has narrow safe operating area.	The safe operating area of IGBT is wider than that of BJT.
Power handling capacity	The power handling ability of a BJT is lower than IGBT.	IGBT can handle more power compared to BJT.
ON-state resistance temperature coefficient	BJT has negative temperature coefficient of ON state resistance.	IGBT has positive temperature coefficient of ON state resistance.
Applications	BJT is used as low power switching device and as an amplifier.	IGBTs are extensively used as switching devices in the inverter circuits.

Conclusion

As is evident from the above table, there are several differences between bipolar junction transistor (BJT) and insulated gate bipolar transistor (IGBT). Both of these transistors are widely used as amplifiers and switching devices. One should have a good understanding of how BJTs and IGBTs function in order to select either of them according to exact requirements of an application.