IGBT (Insulated Gate Bipolar Transistor)

What is an IGBT: -

IGBT stands for Insulated Gate Bipolar Transistor. It is a 3-terminal semiconductor device normally used for digital transfer. The terminals are:

• Collector (C)
• Emitter (E)
• Gate (G)

An IGBT has capabilities via controlling the go with the flow of electrical current between the collector and emitter using a voltage applied to the gate. It operates in addition to a MOSFET in its control mechanism and like a BJT in its conduction mechanism.

In easy phrases, an IGBT is a voltage-controlled device that enables large currents and high voltages to be switched on and off correctly.

Construction of IGBT: -

The IGBT combines the input traits of a MOSFET with the output traits of a BJT, resembling the shape of an N-channel MOSFET and a PNP BJT in Darlington configuration. Additionally, the resistance of the flow path can be integrated. In terms of the IGBT's structure, there is more than one present-day path. The number one route is from the collector to the emitter, involving the series "collector, P substrate, N-, P, emitter", which aligns with the PNP transistor. There's also a secondary path: "collector, P substrate, N-, P, N, emitter," which necessitates the inclusion of any other NPN transistor, as illustrated within the figure below.

The IGBT includes 4 semiconductor layers organised to create a PNPN structure. The collector (C) electrode connects to the P layer, whilst the emitter (E) is located among the P and N layers. Construction employs a P substrate, with an N layer atop its far-forming PN junction J1. Two P regions are crafted at the N-layer, growing PN junction J2. The gate (G) electrode is positioned inside a gap in the centre of the P vicinity. Metal electrodes serve as the emitter and gate, with the emitter at once linked to the N location and the gate insulated through a silicon dioxide layer. The P layer, known as the injector layer, injects holes into the N layer at the same time as the N layer itself is known as the flow area, with its thickness proportional to voltage-blocking off capability.

The upper P layer is known as the body of the IGBT. The N-layer is designed to establish a contemporary route between the emitter and collector, utilising a channel formed underneath the impact of the voltage applied to the gate electrode. The N-layer is strategically designed to offer a direction for the current to flow.

IGBT  CONSTRUCTION

Working of IGBT: -

IGBT has 3 terminals: collector (C), emitter (E), and gate (G). These terminals serve awesome roles in controlling current flow through the device; the collector and emitter are related to the conductance direction, while the gate terminal is responsible for controlling the tool and IGBT operation. In the operation of an IGBT, the collector-emitter connection is mounted with the collector at a higher voltage compared to the emitter. These are forward biases at junction J1 and reverse biases at junction J2.

Notably, there is no voltage applied to the gate at this degree. Due to the reverse bias at J2, the IGBT stays within the off kingdom, stopping any modern-day glide between the collector and emitter. When a tremendous gate voltage (VG) is implemented relative to the emitter, negative charges collect below the SiO₂ layer due to capacitance. As VG increases, more fees are gathered, forming a layer within the higher P-area while VG exceeds the threshold voltage.

This layer successfully creates an N-channel that connects the N-glide place and N-area. Electrons from the emitter then go with the flow from the N vicinity into the N-glide place, while holes from the collector are injected from the P region into the N-drift area. The excess of both electrons and holes within the drift location enhances its conductivity, enabling current conduction. Consequently, the IGBT switches on and permits current to go with flow between the collector and emitter.

IGBT may be managed or flipped ON or OFF simply by activating or deactivating the gate terminal. As the fantastic enters the voltage, then it's going to turn ON state, and because the input voltage is going to 0 or bad, then it will likely be flipped OFF. Additionally, it has low channel resistance, which ends within the clean flow of modern-day inside the tool.

V-I Characteristics of IGBT: -

IGBTs differ from BJTs in that they're voltage-managed devices requiring, most effectively, a small gate voltage, VGE, to adjust the collector's present day, IC. However, the gate-emitter voltage, VGE, needs to surpass the brink voltage, VGET. The switch traits of IGBT illustrate the relationship between the input voltage, VGE, and the output collector edge, IC.

When VGE is 0V, the tool stays off and is not using an IC, and when VGE barely increases but stays under VGET, it stays off but may exhibit a leakage in the present day.

Once VGE surpasses the brink, IC begins to upward push, turning the device on. As a unidirectional tool, modern flows best in one route.

IGBT function curves, as depicted inside the supplied graph, reveal the relationship among collector present day, IC, and collector-emitter voltage, VCE, at distinct VGE degrees.

At VGE < VGET, the GBT is in cutoff mode, resulting in IC = 0 at any VCE. Beyond VGE > VGET, the IGBT enters the energetic mode, wherein IC will increase with growing VCE.

Moreover, for every VGE wherein VGE1 < VGE2 < VGE3, IC differs. It's crucial not to exceed the opposite voltage or forward voltage beyond their respective breakdown limits, as this will lead to uncontrolled contemporary float.

Types of IGBTs: -

IGBTs can be classified into two major types:

Punch-Through (PT) IGBTs:

• Have a buffer layer.
• Faster switching.
• Suitable for lower switching frequency applications.

Non-Punch-Through (NPT) IGBTs:

• No buffer layer.
• Slower but can handle higher voltages.
• Better short-circuit ruggedness and temperature stability.

Applications of IGBT: -

IGBTs are extensively used in various high-power and high-efficiency applications, including:

1. Industrial Motor Drives

• Variable frequency drives (VFDs)
• AC and DC motor controllers

2. Electric and Hybrid Vehicles

• Inverter circuits for motor control
• DC-DC converters
• Battery management systems

3. Renewable Energy Systems

• Solar inverters
• Wind turbine converters
• Grid-tie inverters

4. Power Supplies

• Switch-mode power supplies (SMPS)
• Uninterruptible power supplies (UPS)

5. HVDC Power Transmission

• Used in converter stations for high-voltage direct current systems.

6. Induction Heating and Welding

• High-frequency power electronics for metal heating and joining.

Advantages of IGBT: -

• Low Gate Drive Power: Voltage-driven gate control reduces power requirements.
• High Efficiency: Combines low conduction loss of BJT and low drive power of MOSFET.
• Good Thermal Performance: Capable of handling large power loads without overheating.
• High Voltage Ratings: Ideal for high-power applications.
• Easy to Control: Simple gate drive circuits reduce system complexity.

Disadvantages of IGBT: -

• Slower Switching Speed: Compared to MOSFETs, IGBTs switch more slowly.
• Latching Possibility: If not properly designed, IGBTs can latch and fail.
• Tail Current: Due to carrier recombination, turn-off is not as fast.
• More Expensive than MOSFETs: Especially at lower voltage ranges.

Future Trends in IGBT Technology: -

As the demand for electric vehicles and renewable energy systems continues to grow, IGBT technology is also advancing. Some future developments include:

• Trench Gate IGBTs: Offer reduced saturation voltage and switching loss.
• SiC (Silicon Carbide) and GaN (Gallium Nitride) Alternatives: Though IGBTs are efficient, wide bandgap semiconductors like SiC are beginning to replace IGBTs in some high-efficiency systems.
• Improved Packaging and Cooling: Better thermal management techniques to support higher power density.
• Digital Gate Drivers: Intelligent control and diagnostics are being embedded into driver ICs for better system monitoring.

IGBT vs MOSFET vs BJT: - 

Parameter	IGBT	MOSFET	BJT
Control Type	Voltage-controlled	Voltage-controlled	Current-controlled
Switching Speed	Moderate	Fast	Slow
Conduction Loss	Low (moderate VCE)	Low (RDS(on))	Low (VCE)
Input Impedance	High	Very High	Low
Voltage Handling	Very High	Moderate	High
Current Handling	High	Low-Moderate	High
Cost	Moderate	Low	Low

Conclusion: -

The Insulated Gate Bipolar Transistor (IGBT) is a cornerstone of current electricity electronics. Its specific capacity to efficiently switch excessive voltages and currents at the same time as being smooth to control makes it imperative in limitless applications starting from electric powered cars to renewable power systems. Although newer technologies like SiC and GaN are emerging, IGBTs will hold to dominate the panorama in which price-effectiveness, robustness, and high strength-coping with capabilities are required.