# How Class D Chopper Works?

### Class-D Chopper Operation

In our previous post, we have discussed about the basics of chopper and chopper classification.
It is highly recommended to refresh about chopper basics, chopper types.
In this post we are going to see in detail about class D chopper operation.

#### Class-D Chopper - Introduction:

Here the output current is always positive. But the output voltage can be either positive or negative.

• When both V0 and I0 are positive, rectifying operation (Forward motoring ) mode takes place. Here the energy is fed from source to load.
• When the voltage is reversed, inverting operation (Reverse regeneration) takes place. Here the energy is fed from load to source.

#### Operation:

The circuit diagram of the Class D chopper is given below:
From the figure, you can observe that the Class D chopper consists of two switches, two diodes and a DC motor. This type of chopper operates in first quadrant and fourth quadrant.

#### Forward Motoring Operation (Rectifying operation):

• It is the first quadrant operation.
• When switches T1 and T2 are conducting, both the output current (I0) and output voltage (Vo) are positive.
• Now the circuit path will be, Vs - T1 - Load - T2 - Vs.
• The power is flows from the source to load.
• This is known as rectifying operation.
• This operation occurs in first quadrant.(as the current and voltage are positive)

#### Reverse Braking Mode Operation (Inverting operation):

• It is the fourth quadrant operation.
• When switches T1 and T2 are switched OFF, the load inductance generates a huge amount voltage to maintain the current in the same direction.
• The inductance voltage forward biases both diodes D1 and D2.
• Now the circuit path will be Load - D1 - Vs - D2 - Load.
Here the output current is positive but the output voltage is negative. i.e., the power flows from load to source.
• Thus we can achieve reverse breaking operation.
• Here the motor speed can be controlled by changing the duty cycle of the switches.

You may also like to know about other types of choppers operation.

SCR Turn OFF Methods in Chopper Circuits