Which mode is described when the anode is assigned a positive voltage, the gate is assigned a zero voltage disconnected and the cathode is assigned a negative voltage? 

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  1. ON state conducting mode 
  2. Reverse blocking 
  3. OFF state forward conduction mode 
  4. OFF state forward blocking mode 

Answer (Detailed Solution Below)

Option 4 : OFF state forward blocking mode 
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Silicon Controlled Rectifier

An SCR is a 3-terminal and 4-layer semiconductor device.

Anode, Cathode, and Gate are its three terminals.

   F1 Ravi Ranjan Shraddha 02.11.2021 D1    F1 U.B Madhu 29.01.20 D10

Operating modes of SCR

1.) Forward blocking mode

  • In this mode of operation, the anode is given a positive voltage while the cathode is given a negative voltage, keeping the gate at zero potential i.e. disconnected.
  • In this case junction, J1 and J3 are forward-biased, while J2 is reverse-biased, allowing only a small leakage current from the anode to the cathode. 

2.) Forward conduction mode

  • In this mode of operation, the anode is given a positive voltage while the cathode is given a negative voltage, while the gate terminal is provided with a positive pulse
  • In this case, all the junctions are forward-biased. Hence, a current flows from the anode to the cathode.

3.) Reverse blocking mode

  • In this mode of operation, the anode is given a negative voltage while the cathode is given a positive voltage.
  • In this case junction, J1 and J3 are reverse-biased, while J2 is forward-biased, allowing only a reverse leakage current from the cathode to the anode. 
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