Resistor Divider Calculator

[gnasirator]

Hi folks,

ever had to find a combination of resistors to get that voltage divider right, for example to set the output voltage of a step down converter (eg NCP3063)?
If so, wasn't it always a bit cumbersome to look through all available values of the series to find the best trade-off between common values (BOM reusing!) and precision?

Worry no more, this resistor divider calculator finds the best combinations for you and let's you apply constraints like min/max total resistance, max power and gives an overview over the E-series in the results.

I programmed it during the last couple days and found myself already using it a lot. I hope someone out there will find the same and can save some time with it.
It's free for re-distribution. If you have any suggestions about it, please let me know.

Cheers!

[dwpatter53]

Thanks I'll give it a try.
 

[exmadscientist]

Attached is my own (Python) take on this problem. It has a few features many other calculators lack, such as accommodating the two variants of E192 (one includes 919, the other 920  ), and finding the best match including combinations of series (E24 and E96 have slightly different values, which sometimes you can use to your advantage). It also includes a function for "biratio matching", which I think is for three-resistor dividers (as sometimes used in UV/OV lockout circuits, especially on some LTC parts). Past me didn't exactly document it well, though, so who knows what it really does....

Code is rough as I haven't cleaned it up at all for distribution.

License is WTFPL (in essence, public domain). Do whatever you want with it.

[IanJ]

Hi,

Out of interest I have a page on my site with a bunch of web based calculators (javascript).

http://www.ianjohnston.com/index.php/tools

Formula - Time / Hz - Convert Time & Frequency.
Formula - Zener Diode
Formula - Parallel Resistors
Formula - Op-Amp Gain (non-inverting)
Formula - Op-Amp Gain (inverting)
Formula - PPM/DegC - Calculate the change in value of any nominal value (resistance etc) for every degC change.
Formula - Ohms Law - Fill in any TWO numeric values and I'll give you all FOUR.
Formula - LM317 - Fill in the two resistor values(ohms) to compute the output voltage.
Formula - Voltage Divider
Formula - mm to mils

PS. Recently moved to a new server but should all still be working.

Ian.

[Zero999]

Here's one of my favorite web based tools: http://www.random-science-tools.com/electronics/divider.htm

[bktemp]

A great feature in a voltage divider calculator is importing a list of resistors: Often you need to build a divider with the parts you have available right now. But almost all calculators only support input values from the E series.
If you have a list with all resistors in stock including the packages, tolerances etc. you can refine the calculation by automatically removing all parts with a too large package, too low voltage or power rating or too high tolerance.
Another very useful tool: Calculate series/parallel combinations for best possible match for a given resistance value based on the parts available. Here the tolerance calculation gets more interesting, because depending on the ratio of the resistors used, the tolerance of one resistor can be more important than the other one.

[T3sl4co1l]

May be of interest:
http://jansson.us/resistors.html
http://seventransistorlabs.com/Calc/ResDiv.html
http://seventransistorlabs.com/Calc/Thevenin.html

Tim

[Gyro]

You should also try out "Resistor Fun", it's pretty comprehensive:

https://www.eevblog.com/forum/projects/fun-with-resistors/msg729017/#msg729017

[vitormhenrique]

Here's one of my favorite web based tools: http://www.random-science-tools.com/electronics/divider.htm

Awesome! this is going to my favorites NOW!