Why does the SCR remain 'ON' even though the gate pulse is removed?

In summary, the gate pulse being removed does not affect the SCR remaining 'ON' because the junction J2 remains reverse biased. However, the SCR can still regenerate current due to the flow of electrons from cathode to anode in forward conduction mode. This principle does not apply to transistors, which do not regenerate current in the same way. The SCR acts as an electronic switch, turning off when used on AC and staying on when used on DC.
  • #1
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Why does the SCR remain 'ON' even though the gate pulse is removed?

I understood the two transistor model but I want to know the bare physics of it. If you remove the gate pulse only the +ve anode w.r.t. cathode remains, thereby making junction J2 reverse biased hence current should fall of to zero value.

How does the SCR regenerate the current? Current flows from anode to cathode and electrons from cathode to anode(when it is in forward conduction mode). If we apply the principle of operation of SCR to transistor then when when we switch of base-emitter voltage current should flow but this doesn't happen in transistor and only in SCR..

Any help will be highly appreciated...!

Thanks.
 
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  • #2
If you are using the SCR on AC it will turn off as soon the polarity changes, if you are using on DC it will stay on.
this is the equivalent of an electronic switch.
 

1. Why does the SCR stay on after the gate pulse is removed?

The SCR (Silicon Controlled Rectifier) is designed to remain in the 'ON' state even after the gate pulse is removed. This is because once the SCR is triggered, it latches onto the conducting state until the current flowing through it drops below a certain threshold value called the holding current.

2. What is the role of the gate pulse in SCR conduction?

The gate pulse is responsible for triggering the SCR into the conducting state. It provides a small current to the gate terminal of the SCR, which creates a voltage drop across the PN junctions, allowing current to flow through the device.

3. How does the SCR maintain conduction once the gate pulse is removed?

Once the SCR is triggered by the gate pulse, a small leakage current will continue to flow through the device even after the gate pulse is removed. This causes the SCR to remain in the 'ON' state until the current falls below the holding current.

4. Can the SCR be turned off without interrupting the power supply?

Yes, the SCR can be turned off by reducing the current flowing through it below the holding current. This can be achieved by using an external circuit or by waiting for the AC power supply to pass through the zero-crossing point, which naturally reduces the current to zero.

5. Why is the SCR used instead of other types of switches?

The SCR has several advantages over other types of switches, such as high current and voltage handling capabilities, low cost, and low power consumption. Additionally, the SCR can maintain its conducting state without the need for continuous gate control, making it suitable for high-power applications.

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