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Electronics => Beginners => Topic started by: poindexterity on July 22, 2016, 02:06:42 pm

Title: uSupply - 100nF vs 0.1uF
Post by: poindexterity on July 22, 2016, 02:06:42 pm
http://www.eevblog.com/files/uSupplyBenchRevC.pdf (http://www.eevblog.com/files/uSupplyBenchRevC.pdf)

In some places (the PWM filter), Dave uses 0.1uF denoted caps.  In others (ADC input, op amp V+) he uses 100nF.

Why does he use both?  Is it to denote different types of capacitor?  I know the op amp (decoupling?) filters should be ceramic, but don't know what type of nonpolarized cap to use in the filter.  I would assume that it's Tantalum, but I don't really know.
Title: Re: uSupply - 100nF vs 0.1uF
Post by: ebclr on July 22, 2016, 02:09:57 pm
100nF = 0.1uF = 100Kpf

Everything is exactly the same value
Title: Re: uSupply - 100nF vs 0.1uF
Post by: poindexterity on July 22, 2016, 02:11:30 pm
Yes, I'm aware of SI notation.  ;)

My question is this: Why does Dave use both notations on the same schematic?  Why not use 0.1uF everywhere or 100nF everywhere?
Title: Re: uSupply - 100nF vs 0.1uF
Post by: ebclr on July 22, 2016, 02:21:43 pm
It's because he is Australian
Title: Re: uSupply - 100nF vs 0.1uF
Post by: poindexterity on July 22, 2016, 02:48:04 pm
So you're implying that he doesn't intend anything by the different markings.  I can use the same ceramic capacitors in all places that are nonpolarized 0.1uF and 100nF, is that correct?
Title: Re: uSupply - 100nF vs 0.1uF
Post by: ebclr on July 22, 2016, 03:17:03 pm
No, polarized capacitor normally have a + on one side off the schematic,

https://commons.wikimedia.org/wiki/File:Polarized_capacitor_symbol.png
Title: Re: uSupply - 100nF vs 0.1uF
Post by: poindexterity on July 22, 2016, 03:46:22 pm
I don't mean to nitpick, but your responses consistently miss the mark.  I asked:

I can use the same ceramic capacitors in all places that are nonpolarized 0.1uF and 100nF, is that correct?

And you responded:

No, polarized capacitor normally have a + on one side off the schematic,

Can you explain how your response answers my question?
Title: Re: uSupply - 100nF vs 0.1uF
Post by: ZeTeX on July 22, 2016, 03:51:47 pm
So you're implying that he doesn't intend anything by the different markings.  I can use the same ceramic capacitors in all places that are nonpolarized 0.1uF and 100nF, is that correct?
Yes

Title: Re: uSupply - 100nF vs 0.1uF
Post by: T3sl4co1l on July 23, 2016, 12:45:26 am
Laziness. :)

I seek consistency over laziness, so I actively search out any labels that are inconsistent.

I typically label capacitors as:
0.1uF and up
1-99nF
1-999pF

I do not place "0.01uF" and "10nF" simultaneously in the same design.  That would be silly! ;)

Similarly, I have a preferred system for resistors (for which, a thousand is always lowercase 'k', because it's kilo, not Kelvin!) and inductors.

By "typically", I allow for differences between projects, especially when I'm maintaining an existing design.  Someone called a Y1 cap "2200pF"?  Oh well, just make sure the rest do.

Tim
Title: Re: uSupply - 100nF vs 0.1uF
Post by: Rerouter on July 23, 2016, 02:07:46 am
for myself i am an engineering notation kind, so 0-999pF, 0-999nF, 0-X uF, so yes i will call a 2200uF cap 2200uF not 2.2mF,
Title: Re: uSupply - 100nF vs 0.1uF
Post by: ebclr on July 23, 2016, 02:14:27 am
Just because the capacitor have the same value, does not mean they are the same capacitor, this is why you need to make a bom list, some capacitor are optimized to have a good relation volume / capacitance , others to have  low esr, others to have good temperature performance, it's a real science to use the right capacitor at the right place. I doubt Dave take care to have this defined at schematic level since is impossible to differentiate all kinds off capacitor only by the symbol / value notation
Title: Re: uSupply - 100nF vs 0.1uF
Post by: derGoldstein on July 23, 2016, 04:10:08 am
I can think of one example that I've seen a very long time ago for this type of inconsistency, and which I'll occasionally use myself: "0.1uF" means it's a bypass cap, "100nF" means that it's anything else. I'm not at all saying that this is why it's this way here, just that it's just one reason that I've seen it done.

When there are a lot of ICs on a board communicating using SPI or I2C, mixed in with all sorts of comparators and op-amps, you're going to have a ton of small capacitors, half of them probably bypass caps. To make the schematic a bit easier to read, I'd put "0.1uF" for all of the bypass caps, because that's an explicit exception to how I'd normally write that value -- "100nF". That way when I come back to that schematic a couple of years later and try to figure out why everything is laid out the way it is, I can "ignore" the bypass caps. Anyone else looking at the schematic might be annoyed at the inconsistency, but it won't interfere with them reading it.
But that's just me.
Title: Re: uSupply - 100nF vs 0.1uF
Post by: EEVblog on July 23, 2016, 07:42:16 am
My question is this: Why does Dave use both notations on the same schematic?  Why not use 0.1uF everywhere or 100nF everywhere?

I might have copied stuff from other older schematics.
Title: Re: uSupply - 100nF vs 0.1uF
Post by: Brumby on July 23, 2016, 08:33:07 am
I can't say mixing up 0.1uF and 100nF on a circuit has ever worried me.  I've even coped with 0.22uF and 220nF.  ;D
Title: Re: uSupply - 100nF vs 0.1uF
Post by: mrpackethead on July 23, 2016, 09:30:42 am
for myself i am an engineering notation kind, so 0-999pF, 0-999nF, 0-X uF, so yes i will call a 2200uF cap 2200uF not 2.2mF,

yes, i use this as well..    my notation would look like

1p2F  11pF 82pF  680pF
1nF   8n2F
47uF

Resistors are tricky, because i do something bad..   0R012 12R2  1k56   1M56
Title: Re: uSupply - 100nF vs 0.1uF
Post by: Brumby on July 23, 2016, 12:58:54 pm
I can read 6k8 - but I write 6.8k.  Old fashioned, but explicit.
Title: Re: uSupply - 100nF vs 0.1uF
Post by: timb on July 23, 2016, 01:46:38 pm
I can read 6k8 - but I write 6.8k.  Old fashioned, but explicit.

I was brought up with the 6.8k notation, but eventually switched to 6k8, as it's much, much clearer to read. Decimal points can get lost or misread easily. This is also why I use 100n instead of 0.1u almost exclusively.
Title: Re: uSupply - 100nF vs 0.1uF
Post by: StillTrying on July 23, 2016, 02:40:46 pm
I use them all, 0.22u, 220n, and even 0u22, 2R2, 22R, 22K 2K2.

I might have copied stuff from other older schematics.
Did you copy U12A LM358, I think it's a mistake and it's inputs and output won't work up there.
Title: Re: uSupply - 100nF vs 0.1uF
Post by: klunkerbus on July 23, 2016, 02:55:29 pm
At least the days of capacitors being labeled as uuF instead of pF seem to be behind us now...
Title: Re: uSupply - 100nF vs 0.1uF
Post by: Seekonk on July 23, 2016, 06:32:30 pm
I drew a quick schematic for a beginner on a board and noted a resistor should be 10-22K.  He came back the next day all pissed after it blew up in his face.  He said just to be safe he used a 15 ohm. To be safe I no longer write it that way.   Still not sure who was grammatically correct.