Re: LM78XX imput/output capacitors

Hello,

these are minimum values.

the input capacitor doesn't replace the filter capacitor.

for the filter capacitor, take 1000uF per Ampere for 1 volt input variation.

for the output, put big value if you want low impedance...you can add a 220
nF plastic capacitor cause it is better at high frequencies.

Regards

Vincent


"jmariano" <jmariano65@xxxxxxxxx> a écrit dans le message de
news:1189709741.461226.261340@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Dear All,

Sorry if this is a basic question. I deed search the web for an
answer, but could find one.

I'm designing a power supply with various outputs (+24, +15, +10, -15,
-5), using LM78/79XX line regulators. The data*** states that a .1
uF capacitor should be placed at the output to improve transient
response, and a .22 uF at the input, if the regulator is far from the
filter capacitor. But when I look at designs published in journal and
such, I found all kind of variations, including different values for
the input cap., even if
the regulator is close to the filter capacitor (in a PCB), and usually
an additional electrolytic capacitor at output.

So I guess my question are: 1 - do I need a capacitor at input and
what is is value? (and is purpose).
2 - Do I need an additional electrolytic capacitor at output, besides
the 0.1uF, and how do I calculate is value.

If anyone knows of a bibliographic reference ware this things are
explained, I would appreciate.

Regards

José Mariano


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