Concept:In an unregulated supply, the output DC voltage tracks changes in input peak voltage: \( V_{\text{dc}} \propto V_{\text{m,line}} \). A Zener regulator holds the load voltage constant at its reverse breakdown level \( V_Z \).
Formula:$$V_{\text{unregulated}} \propto V_{\text{line}} \quad \text{vs} \quad V_{\text{regulated}} = V_Z = \text{constant} \quad (\text{for } \Delta V_{\text{line}})$$
Solution:- In an unregulated power supply, any change in AC mains voltage directly alters the DC voltage across the filter capacitor.
- Adding a Zener diode shunt regulator absorbs these input voltage variations, keeping the output voltage stable at \( V_Z \).
Why other options are incorrect:- Option A: This reverses the behaviors of regulated and unregulated power supplies.
- Option C: A properly designed Zener regulator delivers a stable, non-oscillating DC output.
- Option D: Zener regulators attenuate input fluctuations rather than amplifying them.
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