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Why do we have capacitors in the input and the output of a regulator?

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iVenky

iVenky

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In the datasheets of voltage regulators I usually see two capacitors (one at the input and another at the output of the regulators). What is the reason for having those?

Thanks a lot:)
 

The short answer is: The input capacitor helps to eliminate noise from the power source and supplies transient currents that would otherwise have to travel through the conductors (which are inductive) from the source. The output capacitor is needed (but not on ALL regulators) for stability, since the regulator is a closed-loop system. The output cap also helps to provide transient currents to the load.
 

Assuming a linear regulator, like a 7805, then the capacitors are there to prevent instability and even oscillation in the regulator. The regulator contains an amplifier and amplifiers can become unstable if their input voltage varies. Some type of regulator are not prone to this and actually do not need the capacitors, but many do and it is always safer to put them in rather than leave them out.

Switching regulators have other issues in addition.

TH has a good read on the matter: https://www.ti.com/lit/wp/snoa842/snoa842.pdf
 

In the datasheets of voltage regulators I usually see two capacitors (one at the input and another at the output of the regulators). What is the reason for having those?

Thanks a lot:)
Click to expand...
Hi Ivenky
I assume that you know about ripple voltage .
Input capacitor or as a matter of fact , bulk capacitor is to decrease input ripple and out put capacitor in linear regulators is used to reduce out put noises and increase ripple rejection ratio .
Best Wishes
Goldsmith
 

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