There is a need of transformer for ___________

Answer: Option B

A centre-tap full-wave rectifier requires a specially designed transformer known as a centre-tap transformer.

This transformer has a secondary winding with a tap at the center, which provides two equal voltages that are 180 degrees out of phase. These voltages are necessary to operate the two diodes in the rectifier circuit, enabling conduction during both halves of the AC cycle.

Option A: half-wave rectifier – A transformer is optional. A half-wave rectifier can work directly on the AC mains without a transformer.

Option C: bridge full-wave rectifier – It does not require a centre-tap transformer. It uses four diodes to rectify both halves of the AC input without needing a center tap.

Option D: none of the above – Incorrect, as Option B clearly requires a transformer.

Hence, a transformer is specifically required for a centre-tap full-wave rectifier.