What cap is this - Page 1
Forum section: electronics / general

author: snipersquad100
author_rank: Frequent Contributor
timestamp: April 13, 2013, 10:58:44 pm
content: Found this schematic but im not sure what cap this is. Symbol show its polarized but the value as far as I know is 3.3uf 63v which is a polyester cap which are not polarized.help please

author: houdini
author_rank: Regular Contributor
timestamp: April 13, 2013, 11:11:53 pm
content: And a tantalum or electrolytic cap cant have this value why?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: April 13, 2013, 11:15:36 pm
content: so its a mistake on the schematic

author: mariush
author_rank: Super Contributor
timestamp: April 13, 2013, 11:20:53 pm
content: Looks like a polarized (the thick part is - ) 3.3uF / 63v electrolytic capacitor.The + side of a capacitor can be connected to ground if there's a split power supply or the capacitor is in front of a negative voltage regulator, for example like in this circuit :In the picture above, C30 and C32's + side is connected to the ground wire. 78L05 above is a +5v linear regulator, and the 79L05 below is a -5v regulator.

author: aargee
author_rank: Frequent Contributor
timestamp: April 13, 2013, 11:31:55 pm
content: A look at the whole section of the circuit would be useful, I'm not sure the capacitor symbol is really showing polarisation, what does the number 5 relate to? Are you saying that the circuit does in fact have a polyester cap in this spot? Polarised and non-polarised electrolytics are available in this value range as are non polarised polyester types.

author: c4757p
author_rank: Super Contributor
timestamp: April 14, 2013, 12:08:57 am
content: Quote from: mariush on April 13, 2013, 11:20:53 pmThe thick part is positive.

author: mariush
author_rank: Super Contributor
timestamp: April 14, 2013, 12:12:33 am
content: Quote from: c4757p on April 14, 2013, 12:08:57 amHmm you may be right... thing is there's so many capacitor notations it's hard to tell with just a small picture. The OP should have posted a larger screenshot.

author: c4757p
author_rank: Super Contributor
timestamp: April 14, 2013, 12:14:57 am
content: The huge number of capacitor notations is really, really annoying. I'm pretty sure about this one, though. That's the style used by KiCad.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: April 14, 2013, 09:45:50 pm
content: Im not sure what cap it is, all I know is what you see in the pic. Its a 555 oscillating circuit, and the number 5 you see is just pin 5 of the 555 timer. I try a electrolytic and breadboard it up. Thanks guys.

author: mariush
author_rank: Super Contributor
timestamp: April 14, 2013, 09:48:56 pm
content: Well, read the datasheet of the 555 and try to understand what those pins do and what that pin's purpose is.After all why are you breadboarding that, don't you actually want to learn what happens there?

author: Unknown
author_rank: Unknown
timestamp: April 14, 2013, 11:31:10 pm
content: Since it's a 555 timer chip, then pin 5 is a control input, but in your case it looks like it's not used; so normally one would use a cap from pin 5 to ground, the -Neg supply rail, to reduce any risk of noise pick-up into pin 5 control.To answer your question; the cap shown is polarised, being a "3.3Mfd or uf" and it might be required ? if, the 555 is driving an output power device that's creating a lot of noise within the circuits DC supply rails... "if that's not the case" and your 555 is on it's own, just doing some simple low power output work, then any non-polarised cap within the value range of 10 to 100nf, would do the job.

author: c4757p
author_rank: Super Contributor
timestamp: April 14, 2013, 11:40:07 pm
content: That is one motherf-ing big cap on a 555 CV pin! I have yet to see a 555 circuit that needs more than 100nF there. The vast majority don't need one at all if you decouple VCC properly.

author: Psi
author_rank: Super Contributor
timestamp: April 15, 2013, 12:01:55 am
content: Yes, when you have that notation (a short thick line and a thin square bracket shape around it) the smaller thick line is positive.It's a bit confusing because it looks kind of like the battery symbol where the longer line is positive.

author: Unknown
author_rank: Unknown
timestamp: April 15, 2013, 08:53:59 am
content: QuoteYes, c4757p is correct... in particular the last section of the reply:QuoteSince we were only able to see just the cap value, and then told it's a 555, the picture becomes that more clear; for members who know this long standing chip, and it's history... with so many variations that were never intended, to become a work-horse beyond it's intended timer function: reference threshold, Schmitt, flip-flop, one-shot, oscillator, and more creative implementations around this chip.