something that always intrigued me about Vrefs

[nordine]

hi there,

yeah , like the title said... is there any difference in Vref points that have two 10k resistors, compared to one with two 1M resistors?

[The Tone God]

http://www.geofex.com/circuits/Biasnet.htm

Andrew

[aron]

I forgot about that great article. It's in the Wiki!

Thanks R.G.!

[nordine]

http://www.geofex.com/circuits/Biasnet.htm

Andrew

spot on, thanks!

[petemoore]

  Question:
  http://en.wikipedia.org/wiki/Ampere
  offshoot..
  I found while searching for
  Ampere
  Ampere Vs. ma.
  Milliampere
  ua [what does the 'u' abbreviate?]
  etc.
  ...and trying to confirm a glimpse/grasp of current consumption 'requirements, comparing 120ua with the 1.7ma - 2.8ma supply current entries on the LM741 data sheet.
  very difficult when I can't reference anything about how to read the numbers...which way the dot moves...<>

[Bobv]

the u (actually Greek Mu i think) generally stands for "micro," or 1/1000 of a milliamp (i think)

[R.G.]

Scientific notation tries to reduce all numbers to a scale of 1 to 1000, plus a suffix which describes 1 to 1000 WHATs.

If you're talking about ordinary things you can hold, 1 to 1000 is good enough without any suffix. If you're talking about thousands, we use the suffix "k" to indicate "thousands" so 1.4 means one and four tenths; 1.4k means one and four tenths thousands. For millions it's "M", and 1.4M means one and four tenths millions.

It works for fractions too. 1.2m (note the lower case "m") means one and two-tenths 1/1000 ths. The indicator for millionths is the greek letter "mu" which most computer keyboards make hard to type, so we commonly use the lower case "u" which is sorta kinda like the official "mu".

From there on you only have to know the suffixes:
E = exa or 10^18
P = peta, or 10^ 15
T = tera or 10^12
G = giga or 10^9
M = mega or 10^6
k or K = kilo or 10^3
no suffix is just units, 1 to 1000
m = milli or 10^-3
u = micro or 10^-6
n = nano or 10^-9
p = pico or 10^-12
f = femto or 10^15

Ideally, every number in scientific notation should have three digits and one decimal, plus a suffix. That covers the range of 1 to 999 and then the suffix makes that range over 10^-15 to 10^+18, a very wide range indeed. There are suffixes for larger and smaller, I just never use them.

So 120uA is the same as 0.120mA is the same as 0.000120A. And it's 120000nanoamps. Each suffix involves moving the decimal point by three places. 0.047uF is a lazy way us USA guys got into of saying 47nF, and strictly speaking is an incorrect way to refer to it. 4700uF is strictly speaking 4.7mF (or 4.7 milli-farads) which we would all confuse with microfarads, so we say 4700uF or 4.7kuF, which is 4.7 kilo-micro-farads, which is a barbarism.

[MartyMart]

That's the GREAT thing about "standards" ................. everyone has their own !!!!