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IGBT Symbol Diagram, Characteristics, Circuit

Aug 08, 2023      View: 3521

IGBT, which stands for Insulated Gate Bipolar Transistors, is a semiconductor device featuring three distinct terminals: the gate, collector, and emitter. This innovative device amalgamates the characteristics of both Bipolar Junction Transistors (BJTs) and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), creating a versatile component that excels in various power electronics applications.



Symbol of IGBT/ IGBT Symbol Diagram
Equivalent Circuit of IGBT
Internal Construction of IGBT
IGBT Characteristics
N Channel IGBT Symbol
P Channel IGBT Symbol
Schematic Symbol Diagram
IGBT Symbol with Diode
What does IGBT stand for?
How does IGBT work?
Who invented the IGBT?
What causes IGBT failure?
What is the difference between IGBT and MOSFET symbols?

Symbol of IGBT/ IGBT Symbol Diagram

The symbol of IGBT combines the characteristics of MOSFET and BJT, reflecting its composite structure and characteristics. The insulating gate of the MOSFET is represented in the symbol, and its structure allows the control signal (input from the gate) to be completely isolated from the main circuit, thereby achieving isolation. However, similar to BJTs, IGBTs also have a current amplification feature that allows current to be amplified in the main circuit. This enables IGBTs to provide low-loss, high-efficiency solutions in applications requiring high-voltage and high-current switching.



IGBT transistor symbol/ insulated gate bipolar transistor symbol

Equivalent Circuit of IGBT


Internal Construction of IGBT

The IGBT functions as a device composed of four layers arranged in a P-N-P-N structure. In the illustration above, distinct regions are highlighted: the Body Region, Drift Layer, Injection Layer, and Metal Layer. Notably, the metal layer linked to the gate terminal is isolated from the semiconductor materials by a layer of Silicon Dioxide (SiO2).


An interesting feature is the connection of two emitter terminals, which are effectively bridged. This arrangement leads to the presence of two significant junctions. The first, named Junction 1 (J1), arises at the interface between the P-layer and the N-layer. The second, designated as Junction 2 (J2), is formed where the P-substrate meets the N-layer.


These junctions are pivotal in the IGBT's operation, facilitating the control of current flow between the various layers. The insulation achieved by the Silicon Dioxide (SiO2) layer serves a crucial role in preventing undesirable current leakage and ensuring the device's efficient and reliable functioning.



IGBT Characteristics


The horizontal X-axis is indicative of the Collector Current (Ic), while the vertical Y-axis represents the Collector-Emitter Voltage (VCE). The diagram above provides a depiction of the IGBT's output characteristics.


In instances where the gate voltage (VGE) maintains a value of zero, the device assumes an off-state, denoted as the Cut-off Region. Here, the IGBT is non-conductive and no current flows between the collector and emitter.


Upon a gradual rise in gate voltage, staying below the threshold voltage, a minute leakage current emerges, yet the IGBT remains situated within the cut-off region, maintaining its non-conductive status.


However, surpassing the threshold voltage with an elevation in gate voltage propels the device into an active state, referred to as the Active Region. Within this region, current becomes capable of traversing through the IGBT. Moreover, the extent of current flow can be augmented by elevating the gate voltage further.


As the IGBT advances into the saturation region, the current flow levels out, reaching a constant value. Here, even with an increase in the gate voltage, the current no longer experiences enhancement, presenting a stabilized conduction state.

N Channel IGBT Symbol

Just like with the general IGBT, the specific pin arrangement and symbols used can vary based on the manufacturer and model. Always refer to the datasheet provided by the manufacturer for accurate information about a particular N-channel IGBT device.

Simplified equivalent circuit and electrical graphical symbols of N-channel IGBT



P Channel IGBT Symbol

Read more:


Schematic Symbol Diagram


igbt schematic symbol

IGBT Symbol with Diode



What does IGBT stand for?

IGBT stands for "Insulated Gate Bipolar Transistor."


How does IGBT work?

Off State (Cut-off Region): When the gate voltage (VGE) is below a certain threshold, typically a few volts, the IGBT remains in the off state. In this condition, there is no significant current flow between the collector and the emitter.

Turn-On Process (Active Region): When the gate voltage exceeds the threshold value, it causes a current to flow into the gate terminal. This triggers the formation of a conductive channel between the N-drift region (similar to the N-channel in a MOSFET) and the P+ substrate. Electrons are injected from the N-drift region into the P+ substrate (holes are injected in the opposite direction), forming an N-P-N transistor structure. This process turns on the IGBT, and it enters the active region.

Conduction: In the active region, the IGBT allows current to flow between the collector and emitter. The IGBT's conductivity is controlled by the voltage applied to its gate terminal. A small voltage on the gate can lead to a significant collector current, making it a power amplifier.

Turn-Off Process: To turn off the IGBT, the gate voltage is lowered, reducing the current flowing into the gate. The N-P-N transistor structure is cut off, blocking the flow of majority carriers (electrons) from the N-drift region to the P+ substrate. This process interrupts the conductivity between the collector and emitter, returning the IGBT to the off state.


Who invented the IGBT?

The Insulated Gate Bipolar Transistor (IGBT) was invented by two Japanese engineers, Dr. Kawamura and Dr. Yasuda, who were working at the power electronics company Mitsubishi Electric Corporation. They developed the IGBT in the 1980s as a result of their efforts to combine the high switching speed of MOSFETs with the high current-carrying capability of bipolar transistors.


What causes IGBT failure?

Some common causes of IGBT failure include:

Overvoltage or Voltage Spikes

Overcurrent or Current Surges

Short-Circuit Currents

Switching Stress

Temperature Extremes

Aging and Wear

Voltage Ratings

Gate-Source Overvoltage

Electrostatic Discharge (ESD)

Contamination and Foreign Particles

Manufacturing Defects

Poor Cooling

Mechanical Stress

To prevent IGBT failures, proper circuit design, appropriate protective circuits (like snubbers, clamps, and freewheeling diodes), and following manufacturer recommendations for voltage, current, temperature, and switching frequency are essential. Additionally, maintaining proper cooling and ensuring proper handling during installation and maintenance can extend the lifespan of IGBTs and minimize failure risks.


What is the difference between IGBT and MOSFET symbols?

IGBT is well-suited for medium to very high current conduction and control, while MOSFET is more appropriate for low to medium current conduction and control.

In terms of frequency performance, IGBT exhibits limitations, performing effectively up to a few kilohertz frequency. In contrast, MOSFET excels in high-frequency applications, demonstrating its prowess at megahertz frequencies.

When it comes to switching speed, IGBT is characterized by a notably slower switching speed. Conversely, MOSFET offers the advantage of rapid switching capabilities.

In the realm of voltage and power handling, IGBT shines by effectively managing very high voltage and power levels. In contrast, MOSFET is better suited for applications involving lower to medium voltage and power.

The forward voltage drop during current conduction sets IGBT apart, showcasing a lower forward voltage drop compared to MOSFET.

As for turnoff time, IGBT exhibits a longer turnoff time, in contrast to MOSFET, which demonstrates a smaller turnoff time.

The configuration of terminals distinguishes these devices further: IGBT's terminals include Emitter, Collector, and Gate, while MOSFET comprises Source, Gate, and Drain terminals.

Considering their construction, IGBT incorporates a PN Junction, unlike MOSFET, which lacks such a feature.

In terms of transient voltage handling, IGBT excels by accommodating transient voltage and current without major operational disturbances. Meanwhile, MOSFET's operation can be affected by transient voltage.

The cost factor sets IGBT and MOSFET apart, with IGBTs generally being higher-cost devices, while MOSFETs tend to be more cost-effective.

IGBTs find their stride in high-power AC applications, while MOSFETs are particularly well-suited for low-power DC applications.


Read More:

Difference Between BJT, MOSFET and IGBT: BJT vs MOSFET vs IGBT

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Application of IGBT and IGBT Application Examples
IGBT Symbol Diagram, Characteristics, Circuit
Global IGBT Shortage: Cause & Future Outlook
IGBT Rectifier: All You Want to Know
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Difference Between IGBT and MOSFET (IGBT vs MOSFET)
What is the Advantage of IGBT

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