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Consider the following statements with regards to IGBTs : 1. At the highest temperature, maximum current rating goes down to 2/3 value. 2. IGBT is the preferred device for applications that require high blocking voltages and lower operating frequencies. 3. Turn-on transients are identical to MOSFETs. Which of the above statements are correct? 

Consider the following statements with regards to IGBTs : 1. At the highest temperature, maximum current rating goes down to 2/3 value. 2. IGBT is the preferred device for applications that require high blocking voltages and lower operating frequencies. 3. Turn-on transients are identical to MOSFETs. Which of the above statements are correct?  Correct Answer 1 and 3 only

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:

[ alt="F1 Nakshatra Madhuri 15.12.2021 D5" src="//storage.googleapis.com/tb-img/production/21/12/F1_Nakshatra_Madhuri_15.12.2021_D5.png" style="width: 104px; height: 243px;">

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. 

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