An SCR can be turned off by reducing its forward current below:

Explanation:

SCR Turn Off Mechanism

Definition: A Silicon Controlled Rectifier (SCR) is a semiconductor device used in power control and switching applications. It has three terminals: anode, cathode, and gate. An SCR can be turned on by applying a small voltage to the gate terminal, but turning it off requires reducing the anode current below a certain threshold known as the holding current.

Working Principle: In an SCR, the flow of current from the anode to the cathode is controlled by the gate terminal. When a sufficient gate current is applied, the SCR becomes conductive, allowing current to flow through it. To turn off the SCR, the anode current must be reduced below the holding current, which is the minimum current required to keep the SCR in the conducting state.

Correct Option Analysis:

The correct option is:

Option 2: Holding current

This option is correct because the holding current is the minimum current that must be maintained through the SCR to keep it in the conducting state. If the anode current falls below the holding current, the SCR will turn off. This is a fundamental characteristic of SCRs and is crucial for their operation in various applications.

To further understand the concept, let's delve deeper into the other options:

Additional Information

Option 1: Latching current

This option is incorrect. The latching current is the minimum current required to turn on the SCR and maintain it in the conducting state immediately after the gate signal is removed. It is not related to turning off the SCR. Once the SCR is latched, the current needs to be reduced below the holding current to turn it off, not the latching current.

Option 3: Anode current

This option is incorrect as well. While the anode current plays a role in both turning on and off the SCR, the specific threshold for turning off the SCR is defined by the holding current, not just any value of the anode current. The holding current is a precise parameter that dictates the turn-off condition.

Option 4: Cathode current

This option is also incorrect. The cathode current in an SCR is essentially the same as the anode current (considering the device's operation in a series circuit). The critical parameter for turning off the SCR is the holding current, which is defined with respect to the anode current, not the cathode current.

Conclusion:

Understanding the operational parameters of an SCR, such as the holding current, is essential for effective control in power electronics. The holding current is the key parameter for turning off an SCR, and it must be reduced below this threshold to cease conduction. This characteristic distinguishes it from other parameters like latching current, anode current, and cathode current, which have different roles in the SCR's operation.