Diode and capacitor in voltage protection circuit

fishfude · Post by **fishfude** » 18 Jul 2012, 18:55

Hi Folks,

In the image below, I believe the diode and capacitor are there to protect the circuit from too high a voltage coming from the DC power source (correct?). My question is what is the exact purpose of the diode and the capacitor are, and why were they specifically chosen?

http://imgur.com/j1hm9

Many Thanks,

ff

CHEEZOR · Post by **CHEEZOR** » 18 Jul 2012, 19:36

Please wait for someone else who is more knowledgeable to reply, but I believe they are for reverse polarity protection which is meant to save your circuit in the event that someone hooks up the pedal with the polarity opposite what it should be.

Duckman · Post by **Duckman** » 18 Jul 2012, 20:12

Cheezor is right: only a reverse polarity protection, but just the diode.
The cap is for power source filtering... but 22uf? It looks a little "short" since any chinese wall wart can have a 1000uf inside

FiveseveN · Post by **FiveseveN** » 18 Jul 2012, 21:45

More like decoupling rather then filtering.

CHEEZOR · Post by **CHEEZOR** » 18 Jul 2012, 22:19

Duckman wrote:Cheezor is right: only a reverse polarity protection, but just the diode.
The cap is for power source filtering... but 22uf? It looks a little "short" since any chinese wall wart can have a 1000uf inside

Oh yeah. I totally spaced that.

Thanks!

Duckman · Post by **Duckman** » 18 Jul 2012, 23:54

FiveseveN wrote:More like decoupling rather then filtering.

Like in a voltage divider? Mmm... maybe

FiveseveN · Post by **FiveseveN** » 19 Jul 2012, 00:06

http://en.wikipedia.org/wiki/Decoupling_capacitor
There's a duplicate thread on the other forum and another tangent discussion that provides more concise answers.

IvIark · Post by **IvIark** » 19 Jul 2012, 00:28

I think this is semantics of our favoured terminology. Decoupling, power filtering, ripple reducing, the cap can be performing all of the above.

The real mystery is why builders keep using parallel protection diodes without a fuse so that under reverse polarity the diode can take a chunk out of your board.

Duckman · Post by **Duckman** » 19 Jul 2012, 06:34

FiveseveN wrote:http://en.wikipedia.org/wiki/Decoupling_capacitor
There's a duplicate thread on the other forum and another tangent discussion that provides more concise answers.

Tanks. First line of the mentioned article:

This article is about the use of capacitors to filter undesired noise from power supplies.

earthtonesaudio · Post by **earthtonesaudio** » 21 Jul 2012, 00:15

IvIark wrote:I think this is semantics of our favoured terminology. Decoupling, power filtering, ripple reducing, the cap can be performing all of the above.

The real mystery is why builders keep using parallel protection diodes without a fuse so that under reverse polarity the diode can take a chunk out of your board.

No mystery here. Boss did it that way because their 1A diode would get hot (but not burn) when hooked up backward to their 1A PSU. No fuse necessary. Boutiques and diyers copied Boss because... Er, tradition, I guess.