Silicon controlled rectifier ,scr with working principle, construction,characteristics and it's applications.

 INTRODUCTION:-

• SCR stands for silicon controlled rectifier .
• SCR is a four layer device ,it's name as PNPN.
• It has three terminal and three junction also.
• Three terminal name as ANODE,CATHODE and GATE.
• In this device at least one junction in this device are reverse biased.
• Where reverse junction oppose the flow of current. 

Construction diagram 

Symbols of SCR is given below:-

Symbol of SCR 

• The SCR got its name because it is a silicon device which can be used for control or rectification.
• It has 3 PN junction in this device in this device at least one reverse Biased PN junction which is used for opposing conducting current in reverse direction.
• Anode terminal is formed by outer P type material.
• Cathode is formed by outer N  type material.
• Junction J2 are made Gate in this device.

Mode of operation of scr :-

There are three type of mode in this operation.

1. Reverse blocking. 
2. Forward blocking. 
3. Forward construction.  

Reverse blocking:-

When cathode made positive with respect to in the thyristor is in Reverse Biased also known as  reverse biasing. Bhaiya J1 and J 3 are in Reverse bias and J2 are is in forward bias in this mode the thyristor are in OFF state.

Forward blocking:-

When anode is made positive with respect to cathode junction 1 and 3 are in forward bias and J2 are in Reverse bias.

Where J2 junction bill not allowed to flow the current in forward bhaiya only a small leakage current are are bolo then SCR is said to be forward blocking mode.

Forward conduction:-

Here J1 and j3 junction are is in forward bias due to cathode voltage is increased and a Avalanche breakdown are obtained due to large voltage across reverse layer Junction.

Characteristics of scr:- 

• First upon Ig be zero.
• Anode supply Vaa is increased from 0.
• In anode current is increased with anode voltage till to reaches as voltage Vfbo.
• Break over characteristic curve is shown as dotted line and fast switching region.
• Drop across SCR is very small then a node voltage now varies with anode current. 
• In on state voltage drop it slightly increased in anode current due to body resistance.
• After that VT will slightly decrease with increase junction temperature Ia.

Then Once Time again the Sia fire get losses all control over and order Karen and the value of load resistance in external circuit is decreases.

Applications of scr:-

• Speed control of AC and DC motor.

• AC and DC circuit breaker. 

• It is used in 

• temperature control circuit .

• As controlled rectifier where AC is converted into DC .

• it works in inverter where DC is converted into AC .

• it is used as a AC - DC Chopper .

• it is also used as voltage controller.

    Thanks for reading. 

Comments in comments section for any problem.