Jones chopper commutation network In a Jones chopper, which elements form the commutating circuit that provides current reversal for turn-off?

Introduction / Context:
Jones chopper is a class of resonant-commutated DC choppers. It uses a resonant network to apply a reverse current or reverse voltage across the main thyristor, thereby turning it off without relying on line commutation.

Given Data / Assumptions:

• DC supply with a thyristor main switch.
• Auxiliary switch and a resonant commutation branch.
• Commutation requires a controlled reverse current or reverse voltage pulse.

Concept / Approach:
Resonant commutation employs an LC network. When the auxiliary path is fired, the pre-charged capacitor and inductor exchange energy sinusoidally. This creates a transient that opposes the main thyristor current, forcing it to zero and providing reverse bias to complete turn-off.

Step-by-Step Solution:
Charge the commutation capacitor to a defined polarity during conduction.Trigger the auxiliary device to insert the LC across the main thyristor.LC resonance produces a reverse current pulse.Main device current goes to zero and receives reverse bias → successful turn-off.

Verification / Alternative check:
Waveforms show an oscillatory current in the LC branch superimposed on the main current, with the net current through the main thyristor driven to zero.

Why Other Options Are Wrong:

• A capacitor alone cannot produce the required resonant current; an inductor is essential.
• An autotransformer is not a standard element of Jones commutation.
• “None of the above” is incorrect since LC is correct.

Common Pitfalls:

• Mis-timing the auxiliary firing, causing commutation failure.
• Undersized LC leading to insufficient reverse current.

Final Answer:
a capacitor and an inductor