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Electronics Engineering QUESTION #11738
Question 1
In a switching power supply, the output ripple voltage is measured to be excessively high at twice the switching frequency. This is most likely caused by:
  • Incorrect feedback compensation — the control loop is unstable
  • Input EMI filter resonance at the switching frequency
  • High ESR in the output filter capacitor causing resistive ripple✔️
  • Transformer core saturation
Correct Answer Explanation
Output ripple voltage has two components: capacitive ($\Delta V = \Delta Q / C$) and resistive ($\Delta V = \Delta I \times \text{ESR}$). High ESR in electrolytic capacitors dominates ripple in most practical cases and produces ripple at the switching frequency (and harmonics). ESR can be verified with an in-circuit ESR meter or by replacing the capacitor. Unstable loops typically show low-frequency oscillation.