As we know that a chopper is a static device that converts fixed dc input voltage to a variable dc output voltage directly. This characteristic of their operation in any four quadrants form the basis of their classification as class A, class B, class C, Class D, class E, etc.
This type of chopper is also called as two quadrants called type A chopper. This type of chopper is obtained by connecting type A and type B choppers in parallel as shown in the figure given below.
- The output voltage V0 is always positive because of the presence of a freewheeling diode called FD across the load.
- When chopper CH2 is on, or freewheeling diode conducts, output voltage V0 = 0 and in case chopper CH1 is on or diode D2 conduct, the output voltage is equal to the voltage V0 = Vs
- The load current called I0 can, however, reverse its direction.
- Current flows in the arrow direction marked in the figure.
- The load current is positive when CH1 is on or FD operate together as type A chopper in the first quadrant.
- Likewise, CH2 and D2 operate together as type B chopper in the second quadrant.
- Average load voltage is always positive but the average load current may be positive or negative as explained above.
- Therefore, power flow may be from the source to load or from load to source.
- So in Chopper CH1 and chopper CH2 should not be on simultaneously as this would lead to a direct short circuit on the supply lines.
- This type of chopper configuration is used for motoring and regenerative braking of dc motors
- This type of operating region of this type of chopper is shown in figure second by the hatched area in the first and second quadrants.