Transistors are small, semiconductor devices that magnify or switch electric signals and electrical power. Transistors are the basic building blocks of an electric circuit in modern electronics. IGBT and MOSFET are two types of transistors with three terminals used in different devices with various voltages. Let us take a look at what these transistors are and what differences they have.
IGBT vs MOSFET
The main difference between IGBT and MOSFET is that the terminals of IGBT are emitter, collector, and gate, whereas MOSFET is made up of source, drain, and gate terminals. The MOSFET may contain a body terminal at a time. Although, both devices are controlled by voltage.
IGBT is a three-terminal semiconductor switching device used in various devices to amplify or switch between various electric signals. Its terminals are Collector, emitter, and gate. The “collector” and “emitter” are output terminals and the “gate” is the input terminal. It is an ideal semiconductor switching device as it is a cross between Bipolar Junction Transistor (BJT) and MOSFET.
MOSFET is a four-terminal voltage-controlled semiconductor device used in magnifying or switching circuit signals. MOSFETS are by far the most commonly used transistors. It can be made with either a p-type or an n-type semiconductor. Its terminals are a source, drain, gate, and body. Sometimes the body terminal is connected to the source terminal, thus making it a three-terminal device.
Comparison Table Between IGBT and MOSFET
| Parameters of Comparison | IGBT | MOSFET |
| Terminals | Its terminals are collector, emitter, and gate. | Its terminals are the source, drain, gate, and body. |
| Charge carriers | Electrons and holes both are carriers of charge. | Electrons are the major conductors. |
| Junctions | It has PN junctions. | It does not have PN junctions. |
| Switching frequencies | It has a lower switching frequency than MOSFET. | It has a higher switching frequency. |
| Electrostatic discharge | It is highly tolerant to electrostatic discharge. | Electrostatic discharge may be harmful to the metal oxide layer. |
What is IGBT?
The Insulated Gate Bipolar Transistor or IGBT is a transistor that is a cross between BJT and MOSFET. It has the output switching and conduction properties of a BJT but it is voltage-controlled like the MOSFET. Since it is voltage controlled, it requires only a small amount of voltage to maintain conduction through the device.
IGBT combines the low saturation voltage of the semiconductor device called transistor and also the high impedance and switching speed of a MOSFET. The device has the capacity to handle large collector-emitter currents with zero gate current drive. Among its three terminals, the collector and emitter terminals are associated with the conductance path, and the gate terminal is linked to controlling the device.
IGBT is ideal for high-voltage and high-current situation applications. It is used for fast switching with high efficiency in several electronic devices. IGBTs are used in various devices like AC and DC motor drives, Switch Mode Power Supplies (SMPS), inverters, Unregulated Power Supply (UPS), traction motor control and induction heating, and many more.
The advantage of using an IGBT is that it offers higher voltage operation, lower input losses, and greater power gain. Although, it can switch current only in the “forward” direction. It is a unidirectional device.
What is MOSFET?
The MOSFET or Metal Oxide Semiconductor Field Effect Transistor is a semiconductor device used to magnify or for the switching of electronic signals. It is a 4-terminal device with the source, drain, gate, and body as its terminals. In some cases, the body and source terminals are connected, bringing the terminal count down to 3.
The charge conductors (electrons or holes), enter the MOSFET via source terminal into the channel and exit via the drain terminal. The width of the channel is controlled by the gate terminal. The gate is located between the source and drain terminal and is isolated from the channel via a thin layer of metal oxide. It is also known as Insulated Gate Field Effect Transistor or IGFET due to the gate terminal being insulated.
A MOSFET is highly efficient even while working at low voltages. It has a high switching speed and has virtually no presence of gate current. It is used in analog and digital circuits, MOS sensors, calculators, amplifiers, and digital telecommunication systems.
Although, MOSFETs cannot work efficiently at high voltage levels as it creates instability in the device and since it has a metal oxide layer it always runs the risk of damage through electrostatic changes.
Main Differences Between IGBT and MOSFET
IGBT and MOSFET are both voltage-controlled but, one main noticeable difference is that IGBT is a 3-terminal device and MOSFET is a 4-terminal device. Although they are very similar, both of them have a few differences between the two transistors.
- IGBT conducts charges through electrons and holes whereas MOSFET carries charges through electrons.
- IGBTs are better in power handling than MOSFETs.
- IGBTs operate at a higher voltage rating than MOSFETs.
- Since MOSFETs have a thin metal oxide layer to separate the gate terminal, they are susceptible to electrostatic discharges. IGBTs, on the other hand, are more tolerant towards high voltages.
- IGBTs are preferred for narrow load variations, whereas MOSFETs are preferred for wide load variations.
- IGBT is preferred for low frequency, high temperature, and low duty cycle applications whereas MOSFET is preferred for high frequency, low temperature, and large duty cycle applications.
Conclusion
IGBTs and MOSFETs are fast replacing the older types of transistors and other mechanical devices used in electrical circuits. Their high efficiency and high switching frequency are fast making them an indispensable part of the circuit. Since both are voltage controlled a choice between them is often difficult.
Even though an IGBT is a cross between a MOSFET and a BJT it is not the best answer in all situations. MOSFETs have also been vastly improved over the years and have shown to be a more dynamic device. However, as IGBTs run efficiently at high voltages and MOSFETs run amazingly well at low voltages, the choice often depends on what output is required of the device.
References
- http://not2fast.com/electronics/theory_docs/choosewisely.pdf
- https://ghioni.faculty.polimi.it/pel/readmat/gate-drive.pdf