Insulated gate Bipolar Transistors (IGBTs) have revolutionized the world of power electronics.
Made by the fusion of Bipolar Junction transistor (BJT) and Metal Oxide Semiconductor Field Effect Transistor (MOSFET), IGBTs have high power handling capabilities. Due to their superior power handling capabilities, IGBTs are being widely used in applications such as electric vehicles, industrial automation, renewable energy systems, etc.
Short for Insulated Gate Bipolar Transistor, IGBT is a three-dimensional semiconductor-switching device that is made by combining MOSFET with BJT. The MOSFET offers high switching speed and an input impedance, but BJT offers high current and voltage carrying capability. This fusion makes IGBTs a superior switching option over older devices such as Gate Turn-off Thyristors (GTOs) and Bipolar Power Transistors (BPTs).
An IGBT is made of three alternating layers of p-type and n-type semiconductors, which are sandwiched between two metal electrodes—an emitter and a collector. These electrodes support current flow through the transistor. A gate terminal also allows you to control the current flow.
Applying a positive voltage to the gate terminal allows current to pass by, creating an electric field. And on the removal of voltage, IGBT turns off, halting the current flow. This IGBT switch is used for on/off switching at high-frequency operations to control the amount of power that flows through the device.
IGBTs are widely used in power electronics because of their unique characteristics and superior features. Below, we have discussed some of the key characteristics of IGBTs:
IGBTs have high power handling capabilities due to their low switching losses and minimum on-state resistance. IGBTs come in a variety of power module configurations. So, it would help if you used an IGBT with a high power configuration for operation at high voltage levels.
One of the main features of IGBTs is their high switching speed. So, they make a perfect fit for high-power operations and high frequencies. This is why they are being widely used for high-frequency applications such as power conversion and motor control.
As mentioned previously, IGBTs have a very low on-state resistance, resulting in very low conduction losses during conduction. This makes IGBTs highly efficient when used in power conversion operations.
IGBTs are very safe to use, with built-in features like short-circuit protection. Besides that IGBTs also have a very high-temperature tolerance, making them a great option for high-temperature power operations.
IGBTs are mainly classified into two types Punch Through IGBT, also known as Asymmetrical IGBT, and Non-Punch Through IGBT, also known as Symmetrical IGPT.
Punch-through IGBTs, also known as asymmetrical IGBTs, are structured as n-(drift), n+(buffer), and p+(anode) regions. The thick P+ anode has a high concentration of dopant. To achieve conductivity modulation, a large number of carriers are injected from the collector, ensuring low on-state voltage.
That said, PT IGBTs have a high switching loss because currents continue to flow until carriers recombine or exit the n- drift region. To reduce the switching loss, a technique called lifetime control is used to make the carriers exit the n-drift region faster by introducing crystal defects in the n- drift region. They are suitable for use in high voltage and current operations where switching frequencies are very low.
PT IGBTs are not able to handle reverse voltages, as they are unidirectional. This is the reason that they are only used in DC circuits such as inverters, microwave ovens, DC motors, etc.
Non-punch-through (NPT) IGBTs, also known as symmetrical IGBTs, are structured as thick n- drift regions (no n+ buffer region) and thin p+ regions with varying dopant concentrations.
This thin P+ region of NPT IGBTs has varying dopant concentrations and controls the carrier injection. Thus, no lifetime control is needed with NPT IGBTs, which is essential in PT IGBTs to reduce switching loss. While NPT IGBTs have low switching loss, they have to increase on-state voltage due to the use of a thicker n- region. These are suitable for lower current and voltage operations with high switching frequencies.
NPT IGBTs are used in AC circuits such as refrigerators, toasters, etc. because their symmetrical structure of NPT IGBTs ensures that forward and reverse breakdowns are equal.
Trench Gate Field Stop Insulated Gate Bipolar Transistor (TG-FS-IGBT), also known as Field Stop Trench IGBTs, is the newest and most advanced version of IGBT. To achieve better performance and effectiveness, it uses a trench structure. In its construction, an extra p-type field stop layer is added to the n-type drift region, which ensures reduced electric field concentration and minimizes on-state voltage drop, improving the device’s overall efficiency.
These advanced IGBTs support faster switching speeds as they have a lower gate charge, making them suitable for high-frequency switching operations and applications. They are commonly used in power inverters, welding machines, motor controllers, etc.
Both IGBT and MOSFET are semiconductors devices used as switches in power electronics for more or less the same purposes, but there are a few differences between the two.
To begin with, while IGBT is a three-terminal (collector, emitter, and gate) semiconductor device, MOSFET is a four-terminal (source, drain, gate, and body) switch. IGBT is more advanced as compared to MOSFET as the fusion makes it MOSFET with BJT.
IGBTs have very high current and voltage-carrying capabilities as compared to MOSFETs and are ideal for high-power operations. On the other hand, MOSFETs have comparatively low on-state resistance, high switching speed, and very low gate drive power, making them suitable for operations requiring high switching frequency.
IGBTs are more advanced and costlier than MOSFETs, which are comparatively cheaper and most commonly used transistors.
High Voltage and Current Rating: IGBTs have very high voltage and current ratings. This is the reason that they are being used for high-power operations such as in electric vehicles, industrial motor controls, renewable energy systems, etc. That said, you should know that IGBTs come in different power modules. So, you should ensure that you are using a suitable one for your power operations.
High Switching Speed: NPT IGBTs have a very fast switching speed and very low switching loss, making them a great option for operations with high switching frequencies, such as inverters.
Low Conduction Losses: PT IGBTs have low on-state resistance and ensure minimum conduction losses, making them suitable for high current and voltage operations.
High Switching Losses: PT IGBTs have a relatively high switching loss, but that can easily be addressed with lifetime control.
Limited Frequency Range: The switching frequency of PT IGBTs is limited due to their high switching losses. But if you are working on an operation with a high switching frequency, you can use NPT IGBT.
Thermal Issues: When not properly managed, IGBTs can cause thermal issues, as they tend to heat up during high power and frequency operations.
Cost: When compared to other power semiconductor devices in the market, IGBTs appear to be a bit more expensive, especially Pt IGBTs.
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