Power supply filter

[DonLee]

Hi everyone I was wondering what is a power supply filter at the beginning of a circuit that I saw on some breadboards not sure if I should use them in my circuits?

[RandomGlitch]

Do you mean a big capacitor across the power supply?

If so, it's no biggie to use it or not use it.  If you are using a battery then there's no need. Otherwise you might be OK you might not. I've always put it in because most designs have it and it's not hard to add.

I've never tested it without myself.

[DonLee]

Yes I see some with 47 cap and other components not sure , but I get some radio interference at the input of this booster circuit I am working on because when I touch only the input cap at the input it gets worse but only at that spot what would be causing that . 

[amptramp]

Yes I see some with 47 cap and other components not sure , but I get some radio interference at the input of this booster circuit I am working on because when I touch only the input cap at the input it gets worse but only at that spot what would be causing that . 

Your body is an effective antenna since your skin is somewhat insulated but bodily fluids are conductive and capacitively connected through the skin to anything you touch.  If you have any non-linear circuitry in the booster, it will amplify the upper and lower half of the radio signal differently, causing an average current drain that follows the envelope of the radio signal, which is the modulation for an AM signal.

[brett]

Hi
The best low frequency filters have ome line resitance ahead of the cap-to-ground. e.g. 3.3 ohm in the supply line before a 22uF cap to ground.
cheers