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IGBT Types: Understanding the Basics

Jul 18, 2023      View: 1184

Introduction

In the world of power electronic systems, Insulated Gate Bipolar Transistors (IGBTs) play a crucial role. These devices offer a unique combination of the advantages of both MOSFETs and BJTs, making them highly efficient for high-voltage, high-current switching applications. In this article, we will delve into the basics of IGBTs, explore their different types, and understand their advantages, disadvantages, and applications.

 

What is an IGBT?

The Insulated Gate Bipolar Transistor (IGBT) is a semiconductor switching device with three terminals, designed for efficient and rapid switching in a variety of electronic applications. These devices are particularly valuable in amplifiers for processing and switching complex wave patterns using pulse width modulation (PWM). The IGBT symbol, illustrated below, visually represents its composition and functionality.

 

As we all know, the IGBT is a combination of the Bipolar Junction Transistor (BJT) and the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). This is also reflected in the IGBT symbol, where the input side represents the MOSFET with the Gate terminal, while the output side represents the BJT with the Collector and Emitter terminals. The Collector and Emitter serve as the conduction terminals, allowing current flow, while the Gate acts as the control terminal, governing the switching operation.

 

V-I Characteristics of IGBT

The Insulated Gate Bipolar Transistor (IGBT) stands apart from the Bipolar Junction Transistor (BJT) in terms of its operating characteristics. Unlike the BJT, the IGBT is controlled by voltage rather than current. It requires only a small gate voltage, referred to as VGE, to govern the collector current. However, it is important to ensure that VGE surpasses the threshold voltage for proper operation.

 

The V-I (Voltage-Current) characteristics of an IGBT demonstrate the relationship between the input voltage, VGE, and the resulting output collector current, IC. When VGE is at 0V, the device remains switched off, and IC is practically nonexistent. At slightly increased VGE levels, below the threshold voltage (VGET), the IGBT remains off, albeit with a small leakage current. It is only when VGE surpasses the threshold limit that IC starts to rise, signifying the activation of the IGBT and the onset of current flow. It is important to note that the IGBT is a unidirectional device, allowing current to flow in a single direction.

V-I Characteristics of IGBT

 

Types of IGBT

Generally speaking, IGBTs can be categorized into two types based on the presence of an n+ buffer layer: Punch-Through IGBT (PT-IGBT) and Non-Punch-Through IGBT (NPT-IGBT). However, there are not just two types of IGBTs. The other three are listed in the table. 

 

Another classification of IGBTs is based on their characteristics, distinguishing them as symmetrical and asymmetrical IGBTs. Symmetrical IGBTs exhibit equal forward and reverse breakdown voltage capabilities, while asymmetrical IGBTs have a lower reverse breakdown voltage compared to the forward breakdown voltage. Symmetrical IGBTs are commonly employed in AC circuits, whereas asymmetrical IGBTs find primary usage in DC circuits, as they do not need to withstand reverse voltage.

 

IGBT Types

Type

Definition

Features

Advantages

Applications

Punch-through IGBT (PT-IGBT)

IGBT with a punch-through layer for improved voltage blocking capability.

High voltage rating, low on-state voltage drop.

medium-power applications

Motor drives, UPS, industrial welding equipment.

Non-Punch-through IGBT (NPT-IGBT)

IGBT without a punch-through layer.

Improved switching speeds, higher power densities.

motor drives, solar inverters, induction heating.

Motor drives, solar inverters, induction heating.

Field Stop IGBT (FS-IGBT)

IGBT with an additional field stop layer.

Enhanced blocking capability, reduced on-state voltage drop.

high-power applications.

Traction systems for electric vehicles, renewable energy converters, high-voltage power supplies.

Punch-through Non-Punch-through IGBT (PT-NPT-IGBT)

IGBT that combines the advantages of PT-IGBTs and NPT-IGBTs.

Low on-state voltage drop, reduced switching losses.

high-frequency applications.

Switch-mode power supplies, plasma generators, high-frequency inverters.

Current Injected IGBT (CI-IGBT)

IGBT that uses current injection to improve switching characteristics.

Lower voltage overshoot during turn-off, reduced switching losses.

resonant converters, high-frequency welders, pulsed power systems.

Resonant converters, high-frequency welders, pulsed power systems.

 

Working of IGBT

The Insulated Gate Bipolar Transistor (IGBT) is composed of four semiconductor layers, with the gate terminal insulated from the semiconductors by a layer of silicon dioxide (SiO2). The structure includes a p+ substrate layer near the collector, an n- layer above it, a p layer closer to the emitter, and n+ layers embedded within the p layer. Junction J2 is formed between the p+ and n- layers, while junction J1 is created between the n- and p layers. The image below depicts the IGBT structure.

 

In its non-conductive state, the IGBT remains dormant without any current flowing from the collector to the emitter, as junction J2 is reverse-biased. However, by applying a positive voltage (VG) to the gate terminal relative to the emitter, the IGBT can be activated. This gate voltage induces a capacitance effect on the SiO2 layer, resulting in the accumulation of positive and negative ions on opposite sides. Consequently, negative charge carriers are injected into the p region, forming a conductive channel between junctions J2. This channel allows current to flow from the collector to the emitter.

 

It's important to note that the applied gate voltage (VG) plays a crucial role in determining the magnitude of the current flow. Increasing the gate voltage enhances the insertion of negatively charged carriers, thereby intensifying the current flow from the collector to the emitter.

 

Conclusion

IGBTs are essential components in power electronic systems, combining the advantages of MOSFETs and BJTs. Understanding the basics of IGBTs, their V-I characteristics, and the different types available is crucial for selecting the right device for specific applications. With their versatility and widespread applications, IGBTs continue to drive advancements in power electronics technology.

 

Read More:

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

IGCT vs. IGBT: What Are the Difference

IGBT vs GTO: Difference Between IGBT and GTO

IGBT Structure, Characteristics and Working Principle
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
IGBT Types: Understanding the Basics
How to Test an IGBT with A Multimeter
Difference Between IGBT and MOSFET (IGBT vs MOSFET)
What is the Advantage of IGBT

Difference Between IGBT and Thyristor 

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FAQ

  • Does IGBT control current or voltage?
  • IGBTs (Insulated Gate Bipolar Transistors) are primarily voltage-controlled devices. The gate terminal of an IGBT requires a voltage signal to control the flow of current between the collector and the emitter terminals. To regulate the current flow through an IGBT, the gate-emitter voltage (VGE) is adjusted. By applying a positive voltage to the gate terminal with respect to the emitter, the IGBT can be turned on, allowing current to flow from the collector to the emitter. Conversely, reducing or removing the gate voltage turns off the IGBT, inhibiting current flow.
  • Can IGBT replace MOSFET?
  • IGBTs have a higher usable current density compared to typical MOSFETs, enabling them to handle significantly greater currents. As a result, a single IGBT device can often replace multiple MOSFETs used in parallel or even supersized single power MOSFETs that are currently available. This characteristic allows for more compact and simplified circuit designs, reducing the need for multiple components and enhancing overall system efficiency.
  • Is IGBT AC or DC?
  • IGBTs (Insulated Gate Bipolar Transistors) are capable of handling both AC (alternating current) and DC (direct current) signals. They are versatile devices that can be used in a wide range of applications involving AC or DC power. IGBTs are commonly used in various power electronic systems, including motor drives, inverters, converters, and power supplies, where they can efficiently switch and control both AC and DC voltages and currents. They are designed to handle high voltages and currents, making them suitable for applications in AC and DC power systems.
  • Is IGBT faster than MOSFET?
  • In general, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are considered to be faster than IGBTs (Insulated Gate Bipolar Transistors) when it comes to switching speeds. MOSFETs have a lower gate capacitance and shorter channel length, allowing for faster switching times and higher frequency operation. IGBTs, on the other hand, have a slower switching speed compared to MOSFETs due to their structure and internal mechanisms. The bipolar nature of IGBTs introduces a delay during the turn-on and turn-off transitions as the minority carriers need to be injected and extracted from the device.
  • How many types of IGBT are there?
  • There are several types of IGBTs available, each with its own characteristics and applications. The main types of IGBTs include: Punch-through IGBT (PT-IGBT), Non-Punch-through IGBT (NPT-IGBT), Field Stop IGBT (FS-IGBT), Punch-through Non-Punch-through IGBT (PT-NPT-IGBT), Current Injected IGBT (CI-IGBT).