Why do the transformer secondary windings in a center-tapped full-wave rectifier experience higher copper losses and req · Electronics MDCAT Past Paper MCQ

Physics Electronics PMDC Conceptual Practice

PMDC Verified Question 331 of 494

Why do the transformer secondary windings in a center-tapped full-wave rectifier experience higher copper losses and require higher VA ratings than in an equivalent bridge rectifier?

Each half of the center-tapped secondary winding carries current for only one half-cycle, resulting in a lower Transformer Utilization Factor (TUF ≈ 0.672 vs 0.812)

Center-tapped transformers convert AC directly into high-voltage direct current

Bridge rectifiers require twice as many secondary transformer windings

Center-tapped rectifiers operate with 100% reactive power losses

Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:

Option A: Each half of the center-tapped secondary winding carries current for only one half-cycle, resulting in a lower Transformer Utilization Factor (TUF ≈ 0.672 vs 0.812)

Concept:

In a center-tapped transformer, each half-winding carries current for only half the total cycle ($ 50\% $ duty cycle), leading to higher RMS heating losses and a lower Transformer Utilization Factor ($ \text{TUF} \approx 0.672 $) compared to a bridge rectifier ($ \text{TUF} \approx 0.812 $).

Formula:

$$\text{TUF}_{\text{center-tapped secondary}} = \frac{P_{\text{dc}}}{2 \cdot V_{\text{half(rms)}} \cdot I_{\text{half(rms)}}} \approx 0.672$$

Solution:

In a center-tapped rectifier, each half of the secondary sits idle during alternate half-cycles.

In a bridge rectifier, the single secondary winding carries continuous AC current on both half-cycles.

This higher winding utilization gives the bridge rectifier a higher TUF ($ 0.812 $), allowing the use of a smaller, more economical transformer.

Why other options are incorrect:

Option B: Transformers handle alternating current and do not rectify AC internally.
Option C: A bridge rectifier uses a single, standard secondary winding without a center tap.
Option D: Secondary losses in both topologies are predominantly resistive (copper losses).

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