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LDO OUTPUT COMPONENTS

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Nikos A.:
Hi everyone,

I was looking some designs and I have some questions regarding some components at the output of the LDOs.

What is the purpose of the inductor used in the circuit below?



 What is the LG1 rated at 1,5A component?

ArthurDent:
LG1 is just a ferrite bead on a lead so its value is quite low. Both of the circuits you show look like they were designed for a SMPS where there would be lots of switching noise. If you Google the spec sheets for this regulator they only show one capacitor on the input and one on the output. Neither circuit looks bad but probably won't add any benefit in a battery powered circuit.

EEEnthusiast:
Some LDOs are conditionally stable with output capacitors. Which means that they can oscillate with very high or very low value capacitors . One of the ways to solve the oscillation is to add a series resistance with the cap. Usually the ESR of tantalum caps serve this purpose. But they do leak a lot. If you use ceramic capacitors which have very less ESR, then it is necessary to add a series resistance to prevent oscillations. The schematic designer chose to add a ferrite bead/inductor to serve as the series resistance. It may offer some additional noise filtering but the main purpose here is to improve the stability of the LDO.

ArthurDent:
As far as stability of the regulator goes and using series resistors or not, I'll go with the information provided by the maker on the spec sheet:

"Output voltages available for the MCP1702 range from 1.2V to 5.0V. The LDO output is stable when using only 1 μF of output capacitance. Ceramic, tantalum or aluminum electrolytic capacitors can all be used for input and output."

Nikos A.:
Thank you guys!! What is the purpose of the inductor at the first circuit? In general, is it a good practice to include LC filters at the output of LDOs for noise suppression?

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