The chopper circuit employing the load commutation technique is known as the load commutation chopper. The load commutation technique is, falling of the load current flowing through the thyristor to zero due to the nature of the load itself.

So that the conducting thyristor gets commutated once the current flowing through it falls below the holding current value. Let us see the circuit diagram, operation, and waveforms of the load commutated chopper.

## Circuit Diagram of Load Commutated Chopper :

The circuit diagram of the load commutated chopper is shown below. The circuit consists of four thyristors (T1, T2, T3, and T4) and a commutating capacitor. The four thyristors operate in two pairs, thyristors T1, T2 form one pair, and thyristors T3, T4 form another pair. The two thyristor pairs are triggered alternatively and conduct load current.

In load commutated chopper, at an instant, there are two main thyristors that conduct load current along with the commutating circuit. Whenever thyristors pair T1, T2 are acting as main thyristors, the thyristors pair T3, T4 along with the capacitor form the commutating circuit.

Whereas, when thyristors pair T3, T4 are acting as main thyristors, the thyristors pair T1, T2 along with the capacitor form the commutating circuit. A free-wheeling diode is connected across the load to free-wheel the inductive load current back to it.

## Working of Load Commutated Chopper :

Now let us see the operation of the above load commutated chopper. In the above circuit, it should be assumed that the losses in diode and thyristors are zero and the load current is assumed to be constant. The operation of the circuit can be explained in the following modes.