Why should we use a film or ceramic capacitor in parallel to electrolytic in linear and switching regulators?
Electrolytic capacitors offer high capacitance values, which makes them excellent for smoothing out low-frequency ripple and providing bulk energy storage. But they’re not so great at handling high-frequency noise due to their relatively high equivalent series resistance (ESR) and inductance.
That’s where ceramic or film capacitors come in. These types have much lower ESR and inductance, making them ideal for filtering out high-frequency noise and transients — exactly the kind of interference you get in switching regulators and even in linear ones with fast load changes.
By placing a ceramic or film capacitor in parallel with an electrolytic, you create a broadband filter: the electrolytic handles the low-frequency stuff, and the ceramic or film mops up the high-frequency noise.
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