What is Full Form of IGBT? Construction, Working, Types and Application

Introduction and Full Form of IGBT

The Insulated Gate Bipolar Transistor (IGBT) is a type of power transistor which integrates an input metal oxide semiconductor (MOS) with an output bipolar transistor. Commonly it is used as a switching device in an inverter circuit and make easier to convert direct current (DC) to alternating current (AC) power. IGBT is used in various application such as household appliances like air conditioner, refrigerator, industrial motor etc.

What is an Insulated Gate Bipolar Transistor?

IGBT is a semiconductor device which combine the features of MOSFET (Metal oxide semiconductor field effect transistor) and a bipolar transistor. It combines both technologies MOSFET and BJT (Bipolar junction transistor). MOSFET is known for high-speed switching capacity and high input impedance, while BJT provides high current gain and low voltage saturation. The structure of IGBT consist of MOSFET like gate, which is used to control the flow of current between emitter and collector and BJT like structure to amplify the current.

IGBT Symbol 

This combination allows IGBT to handle high voltage and current level maintains efficient switching. The symbol of IGBT give send back its dual nature with elements join both MOSFET and BJT. IGBT has large replace power BJT in many high-power applications due to its extensive performance characteristics.

What is Full Form of IGBT?

The Full Form of IGBT is Insulated Gate Bipolar Transistor (IGBT).

Working Principle of IGBT

1. Blocking State: Basically, in the absence of a gate voltage, the IGBT is in a blocking state. Here, minimum current flow through the collector and emitter because of its reverse-biased PNP bipolar transistor’s base-emitter junction.
2. Turn-On: Applying a positive voltage to the gate terminal respective to the emitter begin in the turn-on procedure. This voltage creates an electric field that entice minority carriers (electrons in the P-region, holes in the N-region) against the collector. This action creates a conductive channel through the collector and emitter.
3. Conduction: Once the circuit is turned on, the IGBT allows a crucial current flow between the collector and emitter. This conduction state pursues as long as the gate voltage is maintained properly.
4. Turn-Off: To turn off the IGBT circuits, the gate voltage is decreased or removed. Basically, turning off a MOSFET which directly exhaust charge carriers, and turn off an IGBT includes a more complex procedure. The excess charge carriers in the N drift region require to remove stop conduction effectually. This process is basically reached by requesting a negative voltage or a short pulse to the gate to reverse-bias and the base-emitter junction speed up carrier recombination.
5. Blocking State (Again): Once the gate voltage is removed or decreased below the threshold region, the IGBT returns to its blocking state, effectually hesitant current flow through the collector and emitter.

Structure of IGBT

1. N-Type and P-Type layers: The IGBT has N-Type layer and P-Type layer almost identical to bipolar junction transistor (BJT).
2. Gate Insulator: The gate insulator is used to discrete gate terminal from a semiconductor material.
3. Emitter, Collector and Base Terminal: It is used to control the flow of current in the circuits. In circuit emitter is used to connect N-Type layer, collector is used to connect P-Type layer and gate is used to control the flow current in the circuit.

Construction of IGBT

The IGBT consist of four layers, arranged to make PNPN structure. The collector electrode is connected to P layer while emitter is positioned between the P and N layers. Construction is engaged a P+ substrate with an N- layer is forming the PN junction. The P-type layer is also called as the body of the IGBT. The N-type layer is used to establish the current path between emitter and collector.

The P+ layer is used as injector layer which inject holes in N- layer while N- layer is known as drift region with its thickness proportional to voltage blocking capacity. By varying the voltage, the IGBT can be used to regulate the current flow through the device and makes it easier components in various power electronics application.

Operation of IGBT

When a voltage is applied to the terminal of gate, it creates an electric field which allows or stop the flow of current between emitter and collector as similar to MOSFET.
The IGBT merge the voltage control features of MOSFET and high current carrying capacity of BJT.

It operates as a three-terminal semiconductor device which has features like MOSFET and BJT. In blocking state, it contains minimum current flow between the collector and emitter because of its reverse bias of the PNP bipolar transistor’s base-emitter junction. Basically, applying at positive voltage to the gate comparative to the emitter, an electric field forms, attracting minority carriers regarding the collector and begin a conductive channel, as similar to a MOSFET turn-on process.

This activates high current flow during conduction, continuing as long as the gate voltage survive. To turn off the IGBT, the gate voltage is decrease or removed, required the removal of excess charge carriers in the N drift region, attain between reverse-biasing the base-emitter junction or applying a negative voltage pulse to ease carrier reconsumption. Once the gate voltage drops down below the threshold, the IGBT returns to its blocking state, virtually hesitant current flow between the collector and emitter.

VI Characteristics of IGBT

The VI characteristic, or voltage-current characteristic, of an IGBT explain its behavior about voltage applied across its terminals (collector-emitter voltage, VCE) and the resulting current flowing with it (collector current, IC).

In the on-state, as VCE increases, IC increases sharply until it reaches to saturation point where further increases in VCE result in minimum change in IC. This region exhibits the IGBT low on-state voltage drop, essential for minimizing power losses through conduction.

In the off state, the VI characteristic shows the IGBT blocking capacity. Basically, VCE is at maximum value, while IC is minimum, which indicates the device ability to block current flow when it is not in the conducting state.

Transition between on and off states happens through switching. During turn-on, the IGBT goes into the on-state as the gate voltage increases, which leads to the formation of a conductive channel through the collector and emitter. Basically, during turn-off, it reduces the gate voltage transitions of IGBT into the off state, where the conductive channel closes, obstruct the current flow.

Transfer Characteristics of IGBT

The transfer characteristics of an Insulated Gate Bipolar Transistor (IGBT) describe how the device response to differing input signals and controls the flow of current through its collector and emitter terminals. At its core, the IGBT handle within the control of a gate-emitter voltage (VGE). When (VGE) is enough for positive relative to the emitter, it activates the IGBT to turn on and allows current to transmit within the device from the collector to the emitter. 

As VGE increases above the threshold level, the IGBT enters its active region, differentiate by a linear connection through VGE​ and the collector-emitter voltage (VCE​). In this case, the IGBT acts as a closed switch with minimum voltage drop over it. Basically, when VGE is under the threshold level, the IGBT is in cutoff mode, block current flow and resulting in VCE being actually at its highest value.

These characteristics are essential for designing and controlling IGBT in numerous power electronics applications, and make sure for efficient switching and management of electrical power with minimum loss and exact control over current flow. Understanding these transfer characteristics is crucial for improving circuit performance and efficiency in industrial and automotive applications where IGBT are primary used.

Types of IGBT

1. Non-Punch Through (NPT): In Non-Punch Through (NPT), the N-type drift region does not fully punch through the P-type layer. These design gives good performance and commonly used in low voltage applications.
2. PT (Punch Through): By using Punch Through (PT), the layer is fully punched through drift region and allows circuits for high voltage handling capabilities. It is suitable for high voltage application but have high conduction loss.
3. Trench IGBT: This design provides the use of trench in the semiconductor material and enhance the device performance by reducing the on-state voltage drop and improves the switching characteristics.
4. Field Stop IGBT: This type is used target the minimize the electric field at the collector regions, improves breakdown voltage and reduce condition losses.

Difference between IGBT and BJT

Sr. no.	Parameter	IGBT	BJT
1	Full Form	The Full Form of IGBT is Insulated Gate Bipolar Transistor (IGBT).	The Full Form of BJT is Bipolar Junction Transistor (BJT).
2	Control Type	Voltage-controlled	Current-controlled
3	Switching Speed	Fast	Slow
4	Voltage Rating	High (up to 3kV or more)	Low (typically <100V)
5	Current Rating	High	Moderate
6	Switching Losses	Higher than MOSFET at high frequencies	Higher due to charge storage

Advantages of IGBT

1. Efficiency: It merges the high input impedance of MOSFET with the low on-state power losses of bipolar transistors, and results in sufficient power switching.
2. High Voltage and Current Handling: They can hold high voltages and currents, which make them suitable for high-power applications like motor drives and inverters etc.
3. Ease of Control: They are partially easy to drive, and control as compared to other power devices, which contributing to simplified circuit designs.

Disadvantages of IGBT

1. Switching Losses: IGBT present partially high switching losses as compared to MOSFET, which limits their use in high-frequency applications.
2. Turn-Off Characteristics: Careful thought is required to turn-off characteristics of IGBT to circumvent voltage spark and make sure proper switching behavior.

Application of IGBT

1. Motor Drives: It is used in variable frequency drives (VFDs) and servo drives to control the speed and torque of electric motors.
2. Inverters: It also makes used in DC to AC converters for applications like renewable energy systems and uninterruptible power supply (UPS).
3. Renewable Energy Systems: It works in grid-tied and off-grid renewable energy systems for converting DC power from solar panels or wind turbines into AC power to use in households or industries appliances.
4. Electric Vehicles: IGBT plays a vital role in traction inverters for electric and hybrid vehicles, to control the power flow through the battery to the electric motor.

Challenges and Consideration of IGBT

1. Switching Speed: While faster than traditional BJT, IGBT are slower than MOSFET, limits their use at very high frequency in systems.
2. Temperature Management: Cooling systems is required to manage heat dissipation because of high power densities and switching losses.
3. Overcurrent and Short-Circuit Protection: Because of high-power handling ability, IGBT needs robust protection circuits to avoid damages during overcurrent or short-circuit state.

Also read: MOSFET – Construction, Working Principle, Types, Advantages and Disadvantages

Bipolar Junction Transistor – Construction, Working and Operation

TRIAC- Types, Construction, Working, Advantages and Disadvantages

FET – Field Effect Transistor

Conclusion

In this article, we have studied about Insulated Gate Bipolar transistor (IGBT) structure and types of choosing the right device as per application requirements such as voltage ratings and switching frequency.

FAQ for Insulated Gate Bipolar Transistor (IGBT)