Ever wondered about the technology behind modern power electronics and efficient energy conversion? Enter the Insulated Gate Bipolar Transistor (IGBT), a hybrid power semiconductor device that’s revolutionizing the world of power electronics. In this blog post, we will explore the inner workings of IGBTs, their advantages and limitations, and their real-world applications. So, buckle up and get ready for an electrifying journey into the realm of IGBTs.
Key Takeaways
- IGBT is a hybrid power semiconductor device combining BJT and MOSFET characteristics.
- It offers high voltage and current handling, low on-state resistance, fast switching capabilities suitable for motor drives & traction control applications.
- Careful consideration of mounting type, thermal performance & application requirements essential to select the right IGBT package.
Understanding IGBT: A Hybrid Power Semiconductor Device
The Insulated Gate Bipolar Transistor (IGBT) is a power semiconductor device that merges the benefits of a bipolar junction transistor (BJT) and a power Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), also known as a power mosfet. IGBTs are the perfect blend of high voltage and current handling capabilities with fast switching and low gate current performance. Additionally, the insulated gate rectifier is another component that can be utilized in high voltage applications.
Dr. B. Jayant Baliga, the inventor of the modern IGBT, built upon the fundamental IGBT mode of operation proposed by Y. Akagiri, creating a device now widely used in switch mode power supplies. This revolutionary device has a unique equivalent structure that comprises a MOSFET input and a BJT output, forming a combination of an N-channel MOSFET and a PNP BJT arranged in a Darlington configuration. This structure allows the IGBT to handle positive voltage and function as a type of bipolar power transistor.
IGBTs boast a four-layer semiconductor structure with alternating P and N type properties. This is similar to an NPN transistor, but with an added P layer. The primary characteristic of IGBTs is their ability to inject minority charge carriers from the collector to the emitter, enabling conductivity modulation and low saturation voltage. The gate terminal controls the current flow through the circuit, just like power MOSFETs.
How IGBT Works
The operation of an IGBT relies on using a voltage-controlled gate to regulate the current flow between the collector and emitter terminals, with a MOSFET input and a bipolar transistor output. In other words, it’s a voltage-controlled device that requires only a small voltage to the gate to remain in the conduction state.
Applying a gate voltage (VG) greater than the emitter voltage results in negative charges in a capacitance under the Silicon Dioxide (SiO2) layer. This charge accumulation leads to an interfacial layer which modifies device performance. As VG increases and surpasses the threshold voltage, these charges eventually create a layer in the upper P-region. This layer forms an N-channel, shortening the N- drift region and N+ region, and initiating the conduction of current and switching the IGBT ON.
IGBT Terminology and Symbols
The name “Insulated Gate Bipolar Transistor” (IGBT) originates from its unique circuit symbol, incorporating the symbols of both a bipolar transistor and a MOSFET. The MOSFET gate replaces the BJT base and serves as the controlling terminal, while the emitter and collector are directly connected to a metal coating. The gate, however, is insulated with a silicon dioxide layer that creates a potential difference.
IGBT is known by many other names such as:
- Insulated Gate Transistor (IGT)
- Metal Oxide Insulated Gate Transistor (MOSIGT)
- Gain Modulated Field Effect Transistor (GEMFET)
- Conductively Modulated Field Effect Transistor (COMFET)
These names reflect the unique combination of MOSFET and BJT characteristics present in IGBTs.
IGBT Construction: Delving into the Internal Structure
The IGBT’s internal structure is composed of four semiconductor layers, which form a PNPN structure. The N- layer serves to create a junction between the emitter and collector. This allows for a current flow pathway when a voltage is present at the gate electrode..
This unique construction is the key to the IGBT’s ability to handle high voltage and current levels.
Punch-Through (PT) vs. Non-Punch-Through (NPT) IGBTs
IGBTs come in two main types: Punch-Through (PT) and Non-Punch-Through (NPT), each having a different construction. PT IGBTs include an N+ buffer layer, also referred to as an asymmetrical IGBT, featuring asymmetric voltage blocking capabilities. This means that their forward and reverse breakdown voltages are distinct, with a lower reverse breakdown voltage. PT IGBTs also have a faster switching speed.
NPT IGBTs have the following characteristics:
- They lack a buffer layer and instead have increased robustness and ruggedness due to the wider base and lower gain of the PNP bipolar transistor, also known as the pnp transistor, incorporated within the structure.
- They have a low on-state voltage.
- Their turn-off time is slower compared to other devices.
These characteristics can affect the overall performance of the product.
Operating Principles of IGBT: From Cut-off to Saturation
IGBTs function in various modes such as cut-off, threshold, and forward-biased modes. As a voltage-controlled device, IGBTs require only a small voltage to the gate to remain in the conduction state, and they exhibit unidirectional current flow, meaning that they can only switch current in the forward direction, from collector to emitter.
Input and Output Characteristics
IGBTs’ input and output characteristics encompass voltage-controlled nature, unidirectional current flow, and a linear active region.
The current flowing through the device is directly proportional to the voltage applied to the gate terminal, demonstrating the linear active region behavior of IGBTs.
Switching Behavior
The switching behavior of IGBTs involves charging and discharging the input capacitance to turn the device on and off, with distinct switching waveforms for PT and NPT IGBTs. Charging the input capacitance activates the device, while discharging the capacitance deactivates it, allowing for the rapid and precise control of IGBTs in various applications.
Advantages and Limitations of IGBT Technology
IGBT technology provides numerous benefits, such as the ability to handle high voltage and current, low on-state resistance, and quick switching.
However, it also has its limitations, such as tail current and latch-up issues, which can impact the overall performance of the device in certain applications.
High Voltage and Current Handling
IGBTs’ ability to handle high voltage and current makes them a fitting choice for medium-to-high power applications. They combine the high voltage and current capability of a BJT with the voltage control characteristics of a MOSFET, allowing IGBTs to operate efficiently in a wide range of voltage classes, including:
- 1700V
- 3300V
- 4500V
- 6500V
This makes IGBTs a great choice for applications that require high power and voltage control, such
Low On-State Resistance and Fast Switching
IGBTs exhibit low on-state resistance and fast switching capabilities, making them ideal for power electronics applications that require efficient and rapid power conversion. Their low on-state resistance is attributed to their unique structure consisting of a p-type and an n-type layer, allowing for a low voltage drop across the device.
The fast switching capabilities are due to their high blocking voltage capabilities.
Real-World Applications of IGBTs
IGBTs find use in a variety of practical applications such as:
- Motor drives
- Traction control
- Power conversion
- Inverters
Their high voltage and current handling capabilities, low on-state resistance, and rapid switching make them well-suited for these applications, providing efficient and precise power control.
Motor Drives and Traction Control
IGBTs are commonly used in AC/DC motor drives, UPS systems, and traction motor control for efficient and precise power control. They enable accurate control of motor speed and torque by regulating the current and voltage of the motor, making them an essential component in motor drives and traction control applications.
IGBTs are highly reliable and offer a wide range of features, such as high switching
Power Conversion and Inverters
Power conversion and inverters benefit from IGBT’s fast switching and high voltage capabilities, making them suitable for applications like solar inverters and induction heating systems. IGBTs are employed in inverters to convert DC power into AC power, providing efficient power conversion and control.
Their low on-state resistance and ability to manage high currents make them an optimal choice for power conversion applications.
Selecting the Right IGBT Package
The selection of the correct IGBT package depends on considerations like mounting type, thermal performance, and the requirements of the application. Various package formats and mounting methods are available for IGBTs, each offering its own advantages and drawbacks.
Thru-Hole vs. Surface Mount Packages
IGBTs are available in Thru-Hole and Surface Mount packages, each featuring unique mounting methods and thermal performance characteristics. Thru-hole packages offer increased reliability and ease of repair, along with improved thermal performance, making them better suited for high-power applications.
Surface mount packages, on the other hand, are more cost-efficient and require less board space, making them ideal for high-density applications.
Module Formats and Pre-Designed Functions
IGBT module formats, providing pre-designed functions and reduced production costs, are suitable for high power applications and system integration. These modules are available in a variety of power capacities and are used for a range of applications, including:
- General-purpose drives
- Traction
- Servo-units
- Renewable energy systems
- Motor drives
- Inverters
- High-voltage DC systems
- Power conversion applications
IGBT modules also offer features such as desaturation detection, soft turnoff, and reinforced isolation for enhanced protection and efficiency.
Summary
In conclusion, IGBTs are versatile and powerful devices that have significantly impacted the world of power electronics. They offer numerous benefits, such as high voltage and current handling capabilities, low on-state resistance, and fast switching, making them ideal for a vast array of applications. By understanding their unique characteristics, construction, and operation, engineers and designers can harness the power of IGBTs to create efficient, precise, and reliable power conversion systems for the future.
Frequently Asked Questions
What is an IGBT used for?
IGBTs are commonly used as switching devices in inverter circuits for driving small to large motors, found in home appliances, industrial machinery and automotive applications, to improve efficiency.
Why use an IGBT instead of a MOSFET?
IGBTs are more efficient, produce less audible noise, and have a lower switching loss compared to MOSFETs, making them the preferred choice for high-power applications.
What is the difference between SCR and IGBT?
SCR is a four-layer, three-terminal device with three PN junctions, while IGBT is a three-terminal device with alternating layers and only one PN junction. IGBTs are faster and can be controlled at any time, whereas SCRs are slower and can only be turned on voluntarily. Both devices have comparable conduction losses.
What does IGBT mean on an inverter?
IGBT stands for Isolated-gate Bipolar Transistor, a type of power transistor combining an input MOS and an output bipolar transistor, widely used in inverters.
What are the main components of an IGBT?
An IGBT is a four-layer semiconductor structure which combines the benefits of both a bipolar junction transistor (BJT) and a power MOSFET, forming a PNPN structure.