voltage regulator plus decoupling capacitor?

[ants]

I need to regulate the supply voltage for a 555 timer so I'll be using a LM78 linear voltage regulator with a fixed output of 5V. Does this mean I can remove the 555 timers decoupling capacitor? The voltage regulator has an output decoupling capacitor of its own so I don't think I need two but I'm not certain.

Thanks,

Ant.

 

[DarwinNE]

The venerable 555 is well known to be rugged and easy to use, but it is a little bit prone to show multiple transitions instead of a clean switching at its output, if it is not decoupled appropriately. I am assuming here you want to build one or two prototypes and not fabricating your circuit a million times. If your circuit is physically very small, it *may* be that in some cases the same capacitor will be enough for the regulator and the timer. Anyway, a decoupling capacitor must be placed the closest possible to the IC supply rails, so I would surely use two capacitors if the 555 is farther than 1' from the regulator.
Decoupling cap science does sometimes give unexpected surprises, so be sure to double check that the power supply rails are indeed clean in your prototypes.

 

[palmeiras]

Hi Ants.

If the decoupling capacitor of the regulator is high enough for your case, I think there is no need to keep an extra decoupling capacitor.

 

[ants]

The output decoupling capacitor for the regulator I want to use is mentioned as 10nF in the datasheet. I'd say that is too low so I'll have to keep the 555 decoupling cap.

Thanks,

Ant.