voltage dividers - Page 1
Forum section: electronics / beginners

author: Flump
author_rank: Frequent Contributor
timestamp: June 12, 2014, 02:47:32 am
content: I am making my own voltage referenceusing a precision 10v regulator but I would like multiple taps from it,for instance 10 5 2.5 1.25 , earlier i made a basic series resistor dividerusing two resistors the same value but it wasnt very accurate so i thenreplaced the resistors with a multi turn VR and was able to dial in exactlythe resistance i wanted, but i dont want to have 3 VR's on the board.So I have been looking around for voltage devider IC's but not been able to find anyDoes such an IC exist ?

author: retrolefty
author_rank: Super Contributor
timestamp: June 12, 2014, 02:55:38 am
content: Quote from: Flump on June 12, 2014, 02:47:32 amWhat kind of accuracy do you actually require? Would not using 0.1% resistors (or better) be a solution?

author: Flump
author_rank: Frequent Contributor
timestamp: June 12, 2014, 03:08:55 am
content: yeah fixed resistors would be great, i did not try low tollerance ones before but i do have some0.1% 100K ones so ill try them.i wanted to get the same accuracy as the 10v regulator which is %0.05

author: Stonent
author_rank: Super Contributor
timestamp: June 12, 2014, 03:23:54 am
content: Quote from: Flump on June 12, 2014, 03:08:55 amYou can put the .1% resistors in parallel to get 50K @ %.05

author: Andreas
author_rank: Super Contributor
timestamp: June 12, 2014, 03:57:55 am
content: Quote from: Flump on June 12, 2014, 02:47:32 amHello,Try a LTC1043 capacitive divider.Practical reachable absolute accuracy is some ppm (around 5) for each 2:1 stage.With a stability below 1 ppm.You will need a precision voltage buffer like LTC1050 or LTC2057 at the output of each stage.With best regardsAndreas

author: Dave
author_rank: Super Contributor
timestamp: June 12, 2014, 04:40:07 am
content: Quote from: Stonent on June 12, 2014, 03:23:54 amAccording to statistics, that is incorrect.Two 0.1% resistors would give you a combined tolerance of 0.07%. You would need to use 4 to get 0.05% tolerance.Combined tolerance = tolerance of resistors / sqrt(N)You can read more about this here.

author: Andreas
author_rank: Super Contributor
timestamp: June 12, 2014, 10:22:42 am
content: Quote from: Dave on June 12, 2014, 04:40:07 amHello,You shurely wanted to say "You would need to use 4 with a gaussian error distribution of 0.1% to get 0.05% tolerance"Since the resistors are selected or trimmed the tolerance is usually not with a gaussian spread.With best regardsAndreas

author: Wh1sper
author_rank: Regular Contributor
timestamp: June 12, 2014, 10:49:10 am
content: Take a look to this:Hamon Resistorhttp://conradhoffman.com/HamonResistor.htmlHow to create a precision Resistor decadehttp://www.gellerlabs.com/752AJunior.htm

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: June 12, 2014, 11:00:58 am
content: Quotehttp://www.analog.com/library/analogdialogue/archives/44-04/ad5791.html

author: babysitter
author_rank: Frequent Contributor
timestamp: June 12, 2014, 12:10:31 pm
content: So you want to have standard Voltage and Resistance in your private Cal lab besides Frequency, huh ?Consider using a resistor network consisting of several resistors in a single package. Their temperature tracks closer and the ratio will be more stable due to this compared to single resistors. Also I want to point you to ebay-available settable ratio voltage dividers, look for ESI Dekapot or dekavider. There you have several dials, say three or four decade switches and a poti for the last decade, it all depends on the model. That would be a good fit to a 10 V Source.Also consider a impedance follower on the output to prevent turning your voltage divider into a loaded voltage divider !

author: Flump
author_rank: Frequent Contributor
timestamp: June 12, 2014, 12:27:11 pm
content: Hey babysitteryeah I am making frequency , voltage , capacitance and resistance referenceI know you can buy them from voltagestandard.com but I like making thingsand I am trying to make this cheaply so dekapot or dekavider would break my bankyes I have been using high value resistors in the divider to make sure I do notdraw too many mA from my regulatorso far I have 5v and 10v regulators at %0.05100r and 5k resistors at %0.0515nF cap at %1and some other caps at %0.5once it all worked out I will use a precision resister as a load onone of the regulators to draw about 1mA and that will be my current reference

author: babysitter
author_rank: Frequent Contributor
timestamp: June 12, 2014, 12:45:02 pm
content: OK, so the ESI stuff is out of range. For a resistive divider consider the LT(C?)5400 or some Bourns network.Fine to have the high value resistors in the divider to reduce its current consumption, but this also increases sensitivity to load impedance. OpAmps are your friends to act as buffer / voltage follower so you have a quasi-constant load of almost nothing.

author: Stonent
author_rank: Super Contributor
timestamp: June 12, 2014, 05:17:02 pm
content: Quote from: Andreas on June 12, 2014, 10:22:42 amYou're probably right, I remember hearing that a long time ago, I don't remember the source.

author: Dave
author_rank: Super Contributor
timestamp: June 12, 2014, 09:54:45 pm
content: Quote from: Andreas on June 12, 2014, 10:22:42 amYes, you are right. Assuming a perfect gaussian distribution, that is what you would get.The number of resistors would also have to be significantly higher, if you really wanted to see statistics kicking in, 2 or 4 is much too small.If you were to measure each resistor individually and match them, you would naturally get much better results. Tenfold improvement on tolerance wouldn't be a problem with careful matching.