multiple bypass cap or common bypass cap ? This is the question

Hallo
Showing one of my circuit someone told me that I should put a bypass capacitor for EACH IC I use. Then, I found this guide:



Reading it, I have the impression I should insert only one bypass cap for powersupply.
What it the truth ?

Should I put a bypass cap for each IC like this example:
**broken link removed**

or one for everything:
**broken link removed**

You should do BOTH - and fit the bypass capacitors for each IC as close as possible to it's pins.

Wires and printed circuit traces are inductances. The inductance is a resistance at high frequencies. If your circuit has modern high frequency opamps, digital logic or a microcontroller and if there is only one bypass capacitor at the power supply then the ICs have no bypass at the frequencies they can oscillate at.

Use a bypass capacitor for each IC.

picozero said:

Hallo
Showing one of my circuit someone told me that I should put a bypass capacitor for EACH IC I use. Then, I found this guide:



Reading it, I have the impression I should insert only one bypass cap for powersupply.
What it the truth ?

Click to expand...

You didn't read your referenced article very closely. In the summary section they recommend a bypass cap at every IC, as do we all.

I your circuit uses a few lousy old slow LM324, LM358 or 741 opamps then a single 10uF bypass capacitor is used on a small circuit board.
A 555 IC draws 400mA for a moment each time its output switches so the datasheet for the LM555 recommends two bypass capacitors for it. One 0.1uf and a 1uF to 10uF.

I can hardly remember old fashioned TTL logic but I think they also produced a high output current spike when switching. I always used a 0.1uf ceramic bypass capacitor for each IC.