Which of the following CANNOT be done to minimise the ripple factor in a rectifier?

The ripple factor is a measure of the residual AC component in the output of a rectifier circuit, expressed as the ratio of the RMS value of the AC component to the DC component. Minimizing the ripple factor is crucial in rectifier circuits to ensure a stable and smooth DC output. Various techniques can be employed to achieve this, such as using filters and adjusting the circuit components appropriately.

Correct Option Analysis:

The correct option is:

Option 3: Decreasing the capacitance of the capacitive filter

This option is correct because decreasing the capacitance of the capacitive filter cannot minimize the ripple factor in a rectifier circuit. In fact, reducing the capacitance would increase the ripple factor. A capacitive filter works by charging to the peak voltage of the rectified signal and discharging slowly to provide a smoother DC output. The larger the capacitance, the more charge the capacitor can store, which means the voltage across the load remains more constant, reducing the ripple. Conversely, if the capacitance is decreased, the capacitor discharges more rapidly, leading to a higher ripple factor.

Why Decreasing Capacitance Increases Ripple Factor:

• When the capacitance is reduced, the capacitor cannot store enough charge to maintain a steady voltage during the intervals when the rectifier output voltage drops.
• This results in a larger voltage variation (or ripple) at the output of the rectifier circuit.
• As the ripple factor is directly related to the voltage variation, decreasing the capacitance increases the ripple factor, making the DC output less smooth.

Conclusion: Decreasing the capacitance of the capacitive filter is counterproductive when trying to minimize the ripple factor, which is why it is the correct answer to the question.