Igbt Characteristics MCQ Quiz - Objective Question with Answer for Igbt Characteristics - Download Free PDF

IGBT (Insulated Gate Bipolar Transistor)

• IGBT is a three-terminal device. The three terminals are Gate (G), Emitter (E), and Collector (C).
• An Insulated Gate Bipolar Transistor (IGBT) is a power semiconductor device that combines the advantages of MOSFETs and BJTs.
• Like a MOSFET, it has a high input impedance, which means it requires very little gate current to turn on.
• Like a BJT, it has low conduction (on-state) power loss due to its low saturation voltage.
• It has superior current conduction capability compared with the bipolar transistor.
• It also has excellent forward and reverse blocking capabilities.

The main drawbacks are:

• Switching speed is inferior to that of a Power MOSFET and superior to that of BJT.
• The collector current tails due to the minority carrier causes the turnoff speed to be slow.
• At the highest temperature, the maximum current rating goes down to 2/3 of the value.
• There is a possibility of latch-up due to the internal PNPN thyristor structure.

Explanation:

Insulated Gate Bipolar Transistors (IGBTs)

Definition: An Insulated Gate Bipolar Transistor (IGBT) is a semiconductor device that combines the high input impedance and high switching speeds of Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) with the high current and low saturation voltage capability of Bipolar Junction Transistors (BJTs). This makes IGBTs suitable for high power applications requiring both high efficiency and fast switching.

Working Principle: The IGBT is a three-terminal power semiconductor device, with terminals labeled as collector (C), emitter (E), and gate (G). The device operates by the voltage applied to the gate, which controls the flow of current between the collector and emitter. When a positive voltage is applied to the gate, it creates an electric field that allows current to flow from the collector to the emitter, effectively turning the device on. Removing the voltage from the gate turns the device off.

Advantages:

• High Efficiency: IGBTs have superior on-state characteristics, meaning they exhibit low on-state voltage drops, leading to reduced conduction losses and higher efficiency.
• Good Switching Speed: While not as fast as MOSFETs, IGBTs have good switching speed, which is sufficient for many high power applications.
• High Current Capability: IGBTs can handle high currents, making them suitable for applications such as motor drives, inverters, and power supplies.
• High Voltage Capability: IGBTs can operate at high voltages, which is beneficial for industrial and traction applications.

Disadvantages:

• Switching Losses: Although IGBTs have good switching speed, they are not as fast as MOSFETs, leading to higher switching losses in high-frequency applications.
• Complex Gate Drive Requirements: IGBTs require more complex gate drive circuits compared to BJTs, which can add to the design complexity.

Applications: IGBTs are widely used in applications where high efficiency and high power handling are required. Some common applications include:

• Motor drives and controls
• Inverters for renewable energy systems (e.g., solar inverters)
• Electric vehicle powertrains
• Uninterruptible power supplies (UPS)
• Induction heating and welding equipment

Correct Option Analysis:

The correct option is:

Option 3: Superior on-state characteristics and good switching speed

This option accurately describes the characteristics of IGBTs. They exhibit superior on-state characteristics, which means they have low on-state voltage drops leading to high efficiency. Additionally, they have good switching speed, making them suitable for a wide range of high power applications.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Inferior on-state characteristics and low switching speed

This description is incorrect for IGBTs. IGBTs are known for their superior on-state characteristics and relatively good switching speed. The statement suggesting inferior on-state characteristics and low switching speed does not accurately reflect the performance of IGBTs.

Option 2: Superior on-state characteristics but low switching speed

This option is partially correct but not entirely accurate. While IGBTs do have superior on-state characteristics, describing their switching speed as low is misleading. IGBTs have good switching speed, which is suitable for many high power applications, even though it may not be as fast as MOSFETs.

Option 4: Inferior on-state characteristics but good switching speed

This option is incorrect. IGBTs are characterized by superior on-state characteristics, not inferior ones. While they do have good switching speed, it is the combination of both superior on-state characteristics and good switching speed that defines their performance.

Conclusion:

Understanding the characteristics of IGBTs is crucial for selecting the appropriate device for high power applications. IGBTs offer a unique combination of superior on-state characteristics and good switching speed, making them highly efficient and suitable for various applications such as motor drives, inverters, and power supplies. Despite some limitations in switching speed compared to MOSFETs, IGBTs remain a popular choice due to their high current and voltage handling capabilities.

The correct answer is option 5):(High voltage and low frequency)

Concept:

• IGBTs are extensively used in high-power AC and low-frequency applications such as in inverter circuits.
• MOSFETs are used in low-power DC applications like in power supplies
• IGBT has the ability to handle very high voltage and high power. MOSFET is capable of handling only low to medium voltage and power.
• IGBT can only be used for relatively low frequencies, up to a few kHz. MOSFET can be used for very high frequency (of the order of MHz) applications.
• When IGBT is conducting current, it produces comparatively low forward voltage drop. MOSFET produces a higher forward voltage drop than IGBT.
• For IGBT, the turn-off time is larger than MOSFET. The turn-off time of a MOSFET is smaller than IGBT.
• Hence option 3 is correct.

IGBT (Insulated Gate Bipolar Transistor):

• It is a three-terminal power switch having high input impedance like PMOSFET and low on-state power loss as in BJT (Bipolar Junction Transistor).
• It is a combined form of the best qualities of both BJT and PMOSFET and its turn-on transients are identical to MOSFETs.
• This is the most popular power switch among power-electronics engineers and finds a great variety of applications.
• IGBT is a three-terminal device. The three terminals are Gate (G), Emitter (E), and Collector (C).
   

The circuit symbol of IGBT is shown below:

The main advantages of IGBT over a Power MOSFET and a BJT are:

• It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced.
• Low driving power and a simple drive circuit due to the input MOS gate structure.
• It can be easily controlled as compared to current-controlled devices (thyristor, BJT) in high voltage and high current applications.
• It has superior current conduction capability compared with the bipolar transistor.
• It also has excellent forward and reverse blocking capabilities.
   

The main drawbacks are:

• Switching speed is inferior to that of a Power MOSFET and superior to that of BJT.
• The collector current tailing due to the minority carrier causes the turnoff speed to be slow.
• At the highest temperature, the maximum current rating goes down to 2/3 value.
• There is a possibility of latch-up due to the internal PNPN thyristor structure. 

Insulated Gate Bipolar Transistor (IGBT)

• IGBT is a three-terminal device i.e. gate, collector, and emitter
• IGBT is a voltage-controlled device i.e. +ve gate to emitter voltage (V_GE) is required to turn ON the IGBT.
• IGBT has been developed by combining the best qualities of both BJT and Power MOSFET. Hence, an IGBT exhibits a high input impedance as a PMOSFET and has low ON-state power losses like a BJT.

The correct answer is option 3.

Concept:

• Concept:

  MOSFET - Majority carrier device

  Power BJT, SCR - Minority carrier devices.

  IGBT - Exhibits the properties of both minority carrier and majority carrier devices.

  Minority carrier devices will have stored charge whereas the majority carrier devices don't.

  Explanation:

  Since minority carrier devices like Power BJT and SCR consist of stored charge, these devices take more time to charge and discharge thereby the speed of operation reduces.

  Since power MOSFET is a majority carrier device, it takes less time to charge and discharge, thereby the speed of operation is highest.

  Since IGBT consists of both minority and majority carriers, its speed is less than power MOSFET and more than the power BJT and SCR.

  Increasing speed of operation is SCR, Power BJT, IGBT, power MOSFET

Insulated Gate Bipolar Transistor (IGBT)

• IGBT is a three-terminal device i.e. gate, collector, and emitter
• IGBT is a voltage-controlled device i.e. +ve gate to emitter voltage (V_GE) is required to turn ON the IGBT.
• IGBT has been developed by combining the best qualities of both BJT and Power MOSFET. Hence, an IGBT exhibits a high input impedance as a PMOSFET and has low ON-state power losses like a BJT.

The correct answer is option 4):(MOSFET and BJT)

Concept:

• ​Insulated Gate Bipolar Transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch and it is a voltage-controlled device.
• It is a 4-layer PNPN device.
• The characteristics of IGBT is a combination of MOSFET and BJT
• The on-state losses of an IGBT are lesser than a MOSFET The switching frequency of IGBT is very high compared to BJT. So it is faster than BJT. The IGBT contains a parasitic thyristor

Insulated Gate Bipolar Transistor (IGBT)

IGBT is a three-terminal device i.e. Gate, Drain and Source.

It is the combination of MOSFET and BJT.

IGBT is preferred for making Variable frequency drives (VFD).

This is because IGBT provides a high switching speed necessary for PWM VFD operation.

IGBTs are capable of switching on and off several thousand times a second.

A VFD IGBT can turn on in less than 400 ns and off in approximately 500 ns.

IGBT:

• The IGBT is developed by combining the characteristics of a BJT and a MOSFET
• The on-state losses of an IGBT are lesser than a MOSFET
• The switching frequency of IGBT is very high compared to BJT. So it is faster than BJT.
• The IGBT contains a parasitic thyristor

Important Points

 IGBT:

• Insulated Gate Bipolar Transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch.
• It is a 4 layer PNPN device that combines an insulated gate N-channel MOSFET input with a PNP BJT output in a type of Darlington configuration.

Characteristics:

• High superior ON-state characteristics
• Good switching speed
• Low gate current

IGBT (Insulated Gate Bipolar Transistor):

• It is a three-terminal power switch having high input impedance like PMOSFET and low on-state power loss as in BJT (Bipolar Junction Transistor).
• It is a combined form of the best qualities of both BJT and PMOSFET and its turn-on transients are identical to MOSFETs.
• This is the most popular power switch among power-electronics engineers and finds a great variety of applications.
• IGBT is a three-terminal device. The three terminals are Gate (G), Emitter (E), and Collector (C).
   

The circuit symbol of IGBT is shown below:

The main advantages of IGBT over a Power MOSFET and a BJT are:

• It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced.
• Low driving power and a simple drive circuit due to the input MOS gate structure.
• It can be easily controlled as compared to current-controlled devices (thyristor, BJT) in high voltage and high current applications.
• It has superior current conduction capability compared with the bipolar transistor.
• It also has excellent forward and reverse blocking capabilities.
   

The main drawbacks are:

• Switching speed is inferior to that of a Power MOSFET and superior to that of BJT.
• The collector current tailing due to the minority carrier causes the turnoff speed to be slow.
• At the highest temperature, the maximum current rating goes down to 2/3 value.
• There is a possibility of latch-up due to the internal PNPN thyristor structure. 

Gain-Modulated Field Effect Transistor is also called an IGBT.

1.) Power BJT

• Bipolar Junction Transistor (BJT) is a three-terminal, three-layer, two-junction semiconductor device. Emitter(E), Base(B), and Collector(C) are the three terminals of the device.
• A BJT is capable of handling two polarities (holes and electrons), it can be used as a switch or as an amplifier and is also known as a current control device.

2.) Power MOSFET

• It is a voltage-controlled device and is constructed by three terminals: Source (S), Drain (D), and Gate (G).
• Power MOSFET is specially meant to handle high levels of power.
• These exhibit high switching speeds and can work much better in comparison with other normal MOSFETs in the case of low voltage levels.

3.) IGBT (Insulated Gate Bipolar Transistor)

• IGBT is a semiconductor device having three terminals: Gate (G), Emitter (E), and Collector (C).
• IGBT has been developed by combining the best qualities of both BJT and Power MOSFET.
• Hence, an IGBT exhibits a high input impedance as a MOSFET and has low ON-state power losses like a BJT.

Parasitic Inductance: It is an unwanted inductance effect that is unavoidably present in all practical electronic devices.

As opposed to deliberate inductance, which is introduced into the circuit by the use of an inductor, parasitic inductance is almost always an undesired effect.

From the diode current waveform, it is observed that the current at point 3 has a maximum negative value.

Concept:

1. When switch is modelled as constant voltage drop

Conduction power loss (P) = V_ON I_avg

2. When modelled as a resistance

Conduction power loss (p) = \(\rm I_{rms}^2 R_{ON}\)

3. When modelled as a piecewise linear model

Conduction power loss (P) = \(V_{ON} I_{avg} + I_{rms}^2 R_{ON}\)

Explanation:

Given VI characteristics,

Diagram from Question

As observed from the direction of current given in figure (a), No current will flow through the IGBT. Only diode should be in turn ON to provide path for current.

therefore, conduction power loss can be expressed as

\(\rm P = V_{ON} I_{avg} + I_{rms}^2 R_{ON}\)

\(⇒ P = V_D I + I^2 \left( \frac {dV}{dt} \right)\)

⇒ P = 0.7 × 100 + (100)² × 0.01

∴ P = 170 W