How does an SCR turn off in DC circuits?
2 Answers
An SCR (Silicon Controlled Rectifier) turns off in a DC circuit through a process called **commutation**. Here's how it works:
1. **Natural Commutation**: In a DC circuit, the SCR can turn off when the current through it drops below a certain threshold called the **latching current** (or holding current). This typically happens when the load is resistive, and the load current naturally decreases due to the characteristics of the load or circuit.
2. **Forced Commutation**: In practical DC circuits, especially where natural commutation is difficult to achieve, forced commutation techniques are used. These involve external circuitry designed to reduce the current through the SCR below the latching current. Common methods include:
- **RC Commutation**: An RC network is used to momentarily divert the current away from the SCR.
- **Transformer Commutation**: A transformer is used to induce a voltage that reduces the current through the SCR.
- **Class C Commutation**: This involves adding an additional circuit that provides a momentary reverse current to the SCR to turn it off.
In summary, the SCR turns off either naturally when the current falls below a certain level or through forced commutation techniques when additional control is needed.
1. **Natural Commutation**: In a DC circuit, the SCR can turn off when the current through it drops below a certain threshold called the **latching current** (or holding current). This typically happens when the load is resistive, and the load current naturally decreases due to the characteristics of the load or circuit.
2. **Forced Commutation**: In practical DC circuits, especially where natural commutation is difficult to achieve, forced commutation techniques are used. These involve external circuitry designed to reduce the current through the SCR below the latching current. Common methods include:
- **RC Commutation**: An RC network is used to momentarily divert the current away from the SCR.
- **Transformer Commutation**: A transformer is used to induce a voltage that reduces the current through the SCR.
- **Class C Commutation**: This involves adding an additional circuit that provides a momentary reverse current to the SCR to turn it off.
In summary, the SCR turns off either naturally when the current falls below a certain level or through forced commutation techniques when additional control is needed.
In DC circuits, an SCR (Silicon Controlled Rectifier) turns off through a process known as **natural commutation** or **forcible commutation**. Here's how it works:
1. **Natural Commutation:** In DC circuits, natural commutation happens when the current through the SCR falls below a certain level known as the **holding current**. The SCR can only remain in the conducting state as long as the current through it is above this holding current. Once the current drops below this level (which can be due to a reduction in load or a break in the circuit), the SCR turns off.
2. **Forcible Commutation:** This method involves deliberately reducing the current through the SCR below the holding current using external circuits. This can be achieved by using additional components like a transistor or an inductor that momentarily diverts or reduces the current flowing through the SCR, thereby turning it off.
In AC circuits, the SCR turns off naturally when the AC voltage crosses zero, but in DC circuits, you need to manage the current flow to ensure the SCR can turn off properly.
1. **Natural Commutation:** In DC circuits, natural commutation happens when the current through the SCR falls below a certain level known as the **holding current**. The SCR can only remain in the conducting state as long as the current through it is above this holding current. Once the current drops below this level (which can be due to a reduction in load or a break in the circuit), the SCR turns off.
2. **Forcible Commutation:** This method involves deliberately reducing the current through the SCR below the holding current using external circuits. This can be achieved by using additional components like a transistor or an inductor that momentarily diverts or reduces the current flowing through the SCR, thereby turning it off.
In AC circuits, the SCR turns off naturally when the AC voltage crosses zero, but in DC circuits, you need to manage the current flow to ensure the SCR can turn off properly.