How Class A Chopper Works? Class A Chopper Operation Tutorial

Understanding Class A Chopper Operation Tutorial

We already discussed about the basics and various types of chopper.
Please click here to know more about the Basics of Chopper and various types of Chopper.
In this post, let us see the Class A chopper in detail. Other types of choppers are discussed in separate posts.

Choppers which are not capable of changing the direction of output voltage or output current are known as Single Quadrant choppers.
Thus the Single Quadrant chopper can work in one quadrant only.
It may be in the first quadrant or second quadrant.
The chopper which operates in the first quadrant is called as class A chopper and which operates in the second quadrant is called as Class B choppers.

Class A Chopper Operation:

  • Class A chopper without commutating circuity is shown in the below figure.
    Class_A_Chopper
  • This chopper operates by periodic turn ON and turn OFF of the SCR T1.
  • When this SCR is turned ON the current flows in the direction shown by the arrow through the SCR T1 and load.
  • When the SCR is turned OFF the current passes through diode D1 as shown by the arrow in the figure.
  • Thus it is clear that output current IO can only be positive.
  • Similarly diode D1 limits the output voltage VO to be positive.
  • The region of operation in the VO- IO plane is therefore the first quadrant as shown in the below figure. 
  • The maximum instantaneous voltage VO is limited to the supply voltage Vs when SCR T1 is turned ON.
  • In the class A chopper, the power flow is from the input voltage source to the load connected at the output.
  • As the value of VO is always lower than the input V, it is also called as step down chopper.

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