What is Silicon Controlled Rectifier(SCR), Construction, symbol, Working, Application

Silicon Controlled Rectifier(SCR)

In Power Electronics as well as the whole field of Electronics Silicon Controlled Rectifier(SCR) is a very important and useful device.
In this post, we will discuss only the basic concepts of,
                                 

• What is a Silicon Controlled Rectifier(SCR)? 
• Construction of an SCR
• Symbol of an SCR
• Working principle of an SCR
• Application of an SCR

What is a Silicon Controlled Rectifier(SCR)? 

                               

                             A Silicon Controlled Rectifier(SCR) is a semiconductor device made by Silicon (It is used as the intrinsic semiconductor to which the proper impurities are added). SCR is a three-terminal device. The terminals of SCR are Anode, Cathode, and Gate. The Gate terminal of SCR is also called the control electrode. SCR is also called a unidirectional, Switching Device.

Simple structure and construction of Silicon Controlled Rectifier(SCR):

The basic construction of an SCR is shown below. According to the power rating, there are two types of construction of SCR.

For low-power rating, Planner type construction.

For high-power rating, Mesa-type construction.

For understanding the basic construction of SCR only Planner type Construction of SCR is given below.

                    As you see in the above picture the SCR consists of four different layers pellet of P-type and N-type semiconductor materials. In this construction, all the junctions are diffused.

          The cathode terminal is connected to the most top N-type semiconductor material. Next P-type semiconductor material is connected to the Gate terminal. And the most bottom P-type semiconductor material is connected to the Anode terminal.

Symbol of Silicon Controlled Rectifier(SCR):

Working Principle of a Silicon Controlled Rectifier(SCR):

I will discuss only the basic working principle of SCR. Because before reading deeply you must know the basic workings of an SCR. 

At first, see the structure of an SCR carefully which is given above.

When we applied a positive voltage to the anode with respect to the cathode, J₁ and J₃ will be forward bias but  J₂ will be reverse bias. For current flow through the SCR, all three junctions must be forward-biased. So in this condition, current can not flow through the SCR. This is known as Forward Blocking.
     But when we apply a positive pulse voltage to the Gate terminal the Junction J₂ becomes forward bias and current can flow through the SCR. This is known as Forward Conduction.

              When we apply a negative voltage to the anode with respect to the cathode, J₁  and J₃  will be reverse bias and  J₂ will be forward bias. In this condition, no current can flow through the SCR. This is known as Reverse blocking.

Application of Silicon Controlled Rectifier(SCR):

(1) SCR is used for making controlled AC to DC rectifiers.

(2) SCR is used to make DC to AC Inverter.

(3) SCR is used for switching in the electronic circuit.

(4) SCR is used to control AC as well as DC motors.

Read Also:

• SCR Triggering / SCR Turn On Methods Full explanation.
• How does Electronic CHOPPER Step Up and Step Down the DC Voltage?

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