Question

Arrange the following :
• [A.] SCR anode is made positive with respect to cathode
• [B.] Junction \(J_1\) and \(J_3\) become forward biased
• [C.] Gate current injects minority carriers
• [D.] Regenerative feedback builds conduction
• [E.] Latching current sustains device ON state Choose the correct answer from the options given below :

• A. A, B, C, D, E
• B. B, A, C, D, E
• C. C, B, A, D, E
• D. A, B, C, E, D

Hint:

SCR turn ON sequence: \[ \text{Forward Bias} \rightarrow \text{Gate Trigger} \rightarrow \text{Regeneration} \rightarrow \text{Latching} \]

Answer 1

The Correct Option is A

Concept: The operation of an SCR (Silicon Controlled Rectifier) follows a sequential triggering mechanism. The SCR turns ON through:
• forward biasing,
• gate triggering,
• regenerative action,
• latching process. To determine the correct arrangement, we follow the physical turn-on process of the SCR.

Step 1: Making anode positive with respect to cathode. Initially: \[ \text{Anode is made positive with respect to cathode} \] This places the SCR in forward bias condition. Thus: \[ A \] is the first step.

Step 2: Forward biasing of junctions \(J_1\) and \(J_3\). When forward voltage is applied: \[ J_1 \text{ and } J_3 \] become forward biased, while: \[ J_2 \] remains reverse biased. Therefore second step is: \[ B \]

Step 3: Applying gate current. Now gate pulse is applied. Gate current injects carriers into the SCR structure. Hence: \[ C \] comes next.

Step 4: Regenerative feedback action. Due to transistor action inside SCR: \[ \alpha_1 + \alpha_2 \rightarrow 1 \] Regenerative feedback rapidly increases conduction. Thus: \[ D \] is the next event.

Step 5: Latching of SCR. Once anode current exceeds: \[ \text{Latching Current} \] the SCR remains ON even if gate signal is removed. Hence final step is: \[ E \]

Step 6: Writing the correct sequence. Correct order: \[ A,\ B,\ C,\ D,\ E \]

Step 7: Selecting the correct answer. Therefore correct option is: \[ \boxed{(1)} \]