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Which of the following is false for a Thyristor? A. Thyristor is a majority carrier device B. The forward-bias portion of Thyristor’s i-v characteristics has two stable operating regions. C. The forward-bias portion of Thyristor’s i-v characteristics has one stable operating region. D. The negative gate current turns off the thyristor.

Which of the following is false for a Thyristor? A. Thyristor is a majority carrier device B. The forward-bias portion of Thyristor’s i-v characteristics has two stable operating regions. C. The forward-bias portion of Thyristor’s i-v characteristics has one stable operating region. D. The negative gate current turns off the thyristor. Correct Answer <span style=" line-height: 107%; ">A, C, D</span>

Thyristor:

  • A thyristor is a four-layer semiconductor of a p-n-p-n structure with three p-n junctions.
  • It is a minority carrier device.
  • It has three terminals: the anode, the cathode, and the gate.
  • They are operated as bi-stable switches from non-conducting to conducting state.
  • It is also called a unilateral switch.
  • The junctions along with the thyristor symbol are as shown:

[ alt="F1 S.B Madhu 05.02.20 D1" src="//storage.googleapis.com/tb-img/production/20/02/F1_S.B_Madhu_05.02.20_D1.png" style="width: 194px; height: 246px;">          [ alt="F1 S.B Madhu 05.02.20 D2" src="//storage.googleapis.com/tb-img/production/20/02/F1_S.B_Madhu_05.02.20_D2.png" style="width: 137px; height: 153px;">

  • The anode terminal of the thyristor is connected to the p-type material of a p-n-p-n structure, the cathode terminal is connected to the n-type layer, while the gate of the thyristor is connected to the p-type material nearest to the cathode.
  • Gate terminal in thyristor is used to trigger the device into conduction (latch it) by the application of a small voltage. To trigger, voltage must be applied between the gate and cathode, positive to the gate and negative to the cathode. 
  • The negative gate current can't turns off the thyristor.

 

Characteristics:

The i-v characteristics of thyristor are shown below. In forward-bias portion of the thyristor’s i-v characteristic, there are two stable operating regions i.e. forward blocking mode and forward conduction mode.

[ alt="F1 U.B Madhu 08.04.20 D7" src="//storage.googleapis.com/tb-img/production/20/04/F1_U.B_Madhu_08.04.20_D7.png" style="width: 444px; height: 338px;">

 

Important Points:

SCR has three operating modes.

Forward blocking mode:

  • Anode voltage is made positive with respect to the cathode, with the gate circuit open
  • Both outer junctions are forward biased
  • The inner junction is reversed biased
  • SCR remains in the off state

 

Forward conduction mode:

  • Anode voltage is greater than the forward break over voltage
  • All three junction is forward biased
  • The device is in conduction mode

 

Reverse blocking mode:

  • The cathode is at a higher potential than the anode
  • Both outer junctions are reverse biased (high resistance)
  • The inner (middle) junction is forward biased
  • It is reversed biased and non-conducting

Related Questions

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