A half-wave rectifier is a type of rectifier that only allows one half-cycle of an AC voltage waveform to pass through as it converts AC to DC. Let's analyze the main disadvantage of a half-wave rectifier and identify why the correct answer is "Utilizes only one half-cycle".

Explanation:

• The half-wave rectifier only utilizes one half-cycle of the input AC signal—either the positive half-cycle or the negative half-cycle. Consequently, it only rectifies half of the input signal.
• The efficiency of a half-wave rectifier is lower because it effectively discards half of the input signal. This results in higher power loss and inefficient use of the AC power supply.
• Due to only one half-cycle being used, the output is less smooth and has a higher ripple factor, requiring additional filtering to produce a steady DC output.

Consideration of Other Options:

• Ripple frequency equal to supply frequency: This is indeed a characteristic of half-wave rectifiers, but it is not inherently a disadvantage. Instead, it's a technical specification.
• Requires center-tap transformer: This is not applicable to a basic half-wave rectifier. A center-tap transformer is typically associated with a full-wave rectifier.
• High cost: Half-wave rectifiers are generally less expensive to construct due to their simplicity, making this an incorrect disadvantage.

Conclusion:

The main disadvantage of a half-wave rectifier is that it only utilizes one half-cycle of the input AC signal, leading to lower efficiency and higher ripple in the output. This results in the correct option being: "Utilizes only one half-cycle".