Use of a freewheeling diode in single-phase controlled rectifiers In which of the following single-phase controlled rectifier circuits is it possible and useful to include a freewheeling diode across the DC load?

Introduction / Context:
A freewheeling diode provides an alternate path for inductive load current when the source voltage reverses or the controlled devices are not conducting. Its inclusion depends on the converter topology.

Given Data / Assumptions:

• Single-phase half-wave controlled rectifier (one controlled device).
• Single-phase M-2 (half-controlled full-wave) rectifier with two SCRs and two diodes.
• Inductive load where current continuity is desired.

Concept / Approach:
In the half-wave circuit, during the negative half-cycle the source cannot support load current; a freewheel diode across the DC load allows current to circulate, reducing ripple. In the M-2 topology, although some freewheeling paths exist internally, adding a dedicated freewheeling diode enhances current continuity and improves power factor.

Step-by-Step Solution:
Identify intervals when supply is reverse or devices are off → inductor forces current to continue.Provide a diode across the DC output → current circulates locally, sustaining load current and reducing voltage spikes.Thus, both half-wave and M-2 circuits can employ a freewheeling diode effectively.

Verification / Alternative check:
Standard textbooks show freewheeling diode use in single-phase half-wave and half-controlled bridges to improve current waveform.

Why Other Options Are Wrong:
Only one of the two: Too restrictive.
All controlled rectifiers: Overbroad; some topologies have inherent current paths or different needs.

Common Pitfalls:
Assuming M-2 always eliminates the need; dedicated freewheeling can still improve performance depending on operating conditions.

Final Answer:
single-phase half-wave controlled rectifier and single-phase full-wave controlled rectifier (M-2 connection)