The decoupling capacitor…is it really necessary?

Interesting article to me – thought I’d share


Good easy to read post. Thanks!

Good, I have been building circuits properly. No seriously, good read.

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Excellent article. A good friend of mine used to build all his circuits without them and then I had to debug the board as he couldn’t get it to work. After I hand soldered the caps to the board it started working. Since then he has been a good boy and installed them.

You’d be surprised by the effect of having none. Worth a try one day to build with them but leave them off the boards at first. Strange things start to happen.!! :slight_smile:

Like your Panda II reboots when you plug in an SD card :wink:

@ godefroi - unrelated to this topic. The sd is a power surge not noise during operation.

I disagree. From the article:

That’s exactly what the SD is doing, drawing large amounts of current for a short duration. Because it’s improperly decoupled, the large current draw pulls down the voltage enough that the MCU resets. That’s also why adding the capacitor to the SD socket solves the problem. I could dig up the thread with pictures and explanations, probably.

You are correct. EMI is caused by the rapid switching and the current spikes during switching can cause noise at certain frequencies and this translates to interference generation. It also causes strange things to happen to digital circuits :slight_smile:

Correct guys. Decoupling caps are usually 0.1uf to 0.01uf where the caps needed for surges are 10uf and up.

If you look at the wifi module you will see both, decoupling 0.1uf and one much larger cap.

I guess it depends on where you draw the line between “EMI” and “surge”? I took the quote straight from the article…

Was the article wrong, then? I’m willing to accept that…

Reading Decoupling capacitor - Wikipedia however (specifically the “Decoupling” and “Transient load decoupling” sections seem to support my understanding.