Choppers and commutation; Morgan chopper Assertion (A): A chopper always requires forced commutation. Reason (R): A Morgan chopper uses a saturable reactor for commutation.

Introduction / Context:
DC choppers using thyristors operate on DC without natural current zero crossings. Therefore, they need a method to force devices to turn off. The Morgan chopper is a classic commutation scheme employing a saturable reactor.

Given Data / Assumptions:

• Device: thyristor-based chopper on a DC source.
• No natural current zero in DC, unlike AC line commutation.
• Morgan commutation known as a magnetic (saturable reactor) assisted method.

Concept / Approach:

Since the load and source are DC, the thyristor must be reverse-biased or its current forced to zero by an auxiliary network (LC or magnetic means) to achieve turn-off. This is the essence of forced commutation. The Morgan chopper is one specific method, but the general need for forced commutation exists regardless of whether a saturable reactor is used.

Step-by-Step Solution:

Verification / Alternative check:

Other classes of forced commutation (Class C, D, E, F) use different networks (capacitors/inductors/pulse commutation), underscoring that forced commutation is a general need, not limited to Morgan's method.

Why Other Options Are Wrong:

Options suggesting A is wrong contradict basic SCR behavior on DC. Claiming R explains A would imply Morgan's method alone justifies the need, which is not the case.

Common Pitfalls:

Confusing “one example exists” with “general explanation”; also forgetting that with transistor switches (MOSFET/IGBT), turn-off is controlled, but the question is about SCR-based choppers.

Final Answer:

Both A and R are correct but R is not the correct explanation of A