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The full form of SCR is Silicon Controlled Rectifier. Also known as Semiconductor Controlled Rectifier, SCR is a four-layer solid state current controlling device. It is also the commercial name for the thyristor by General Electric. An SCR is usually used in electronic devices that require high-power regulations and high voltages. This rectifier is used in processes that need medium to high AC (Alternating Current) power. Further, when a gate pulse is applied to an SCR, it conducts current just like diodes.
Table of Contents
Stages of SCR
There are two stages of a Silicon Controlled Rectifier: OFF Stage and ON Stage.
OFF Stage
When the Silicon-controlled rectifier (SCR) is in the off state, the anode receives positive voltages, the gate receives zero voltages, and the cathode receives negative voltages. This results in the first and third junctions being forward biased, while J2 is reverse biased. J2 reaches its avalanche breakdown threshold and starts to conduct. Below this threshold, J1 has a very high resistance and is considered to be off.
On Stage
To enter the ON state, the cathode-anode voltage needs to be increased beyond the avalanche voltage or positive signals need to be applied to the gate. Once the SCR starts conducting, the gate voltage does not need to be maintained for the ON state, and the SCR turns off.
Properties of SCR
Here are the prominent properties of SCR:
- It is used to rectify AC into Direct Current (DC) as it enables unidirectional current flow.
- It can switch high voltages and high currents as it has the ability to handle large power loads.
- It can be triggered into conduction by applying a small control signal to its gate terminal.
- It has built-in overcurrent protection owing to its self-limiting characteristics.
- It has low power dissipation and high efficiency, on account of which it exhibits energy-efficient properties for power conversion and control.
FAQ
An SCR is a souped-up Shockley diode with a gate for precise control of its on-state. This is why it is called what it is called.
SCR, or thyristor for short, is a type of power semiconductor device named after its function (silicon-controlled rectifier) and its structure (PN PN device). It shares its functionality with a gas-filled tube device called a thyratron.
The symbol for a Silicon Controlled Rectifier (SCR) resembles a diode symbol with an additional line representing the gate terminal. This emphasizes its rectifier characteristic while also indicating the control it offers.
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