what caps to use

[andrew2022]

what cap should be used on the input and output from a voltage regulator? i have seen loads of schematics with all different values in and 1 i took out of something had 2 100n ceramic caps. is there a way to work out what size caps to use?

 

[Nigel Goodwin]

what cap should be used on the input and output from a voltage regulator? i have seen loads of schematics with all different values in and 1 i took out of something had 2 100n ceramic caps. is there a way to work out what size caps to use?

They are basically there to prevent the chip oscillating, presumably the manufacturers datasheets will suggest suitable values?.

But it's a very uncritical application, I usually just use whatever falls to hand - usually something between 1uF and 10uF, simply because of their small physical size. It probably wouldn't be a good idea to try and find the minimum value that works, doing so could possibly lead to oscillation under certain conditions.

But I shouldn't worry about, I'd quite happily fit a 100nF, but I usually have more small electrolytics knocking about.

 

[Johnson777717]

I've been studying some of the national semi datasheets on their linear regulators which suggest specific values of capacitors on input / outputs, according to the input-output voltage. Most commonly, the suggestions for capacitor use are indicated in the "Application hints" section of the datasheet (which is normally located within the first few pages of the document) and also within the sample circuits section toward the end of the document. I'm not sure if formulas are provided (I can't remember seeing any for capacitor use).

The most interesting portion of the datasheet that I have found regards the LM317 adjustable regulator, which suggests the use of diodes to protect the regulator from output shorting (located within application hints). I don't think I have seen this diode use in any of the regulator circuits that I have seen on the web. I think it is something to look into, if you're running an adjustable regulator.

 

[chemelec]

A great deal of the regulators recommend a .1 or 1 uF Tantalum on the input and output, Mainly because of there Low ESR.

Take care........Gary

 

[Johnson777717]

and their high frequency response :wink: