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Determine voltage drop across resistors 2013-03-02

AtomSoft

Well-Known Member
AtomSoft submitted a new article:

Determine Voltage Drop Across Resistors - How to calculate voltage drop across series resistors.

Step 1

Determine current of tot

How to calculate voltage drop across series resistors.

Step 1

Determine current of total resistors across the series.

(I = Current/V=Voltage/R(t)=Resistance Total)
I = V / R(t)
I = 9 / (2k + 5k + 10K)
I = .53 mA​

Step 2

Now that we have the Current across the resistors we can calculate the voltage across EACH resistor.

I = Current
Vx = Voltage (x = Current Value across X Resistor)
Rx = Resistor value(x = resistor#)

V = I x Rx...​
Read more about this article...
 

TBotNik

New Member
All,

I have the opposite problem. I have a 15VDC supply across a proposed resistor network that has a 10VDC zener setting the bottom voltage. The resistors have to be configured so that the network is tapped at:

1.) 11.2 VDC,
2.) 11.4 VDC,
3.) 11.6 VDC,
4.) 11.8 VDC,
5.) 12.0 VDC,
6.) 12.2 VDC,
7.) 12.4 VDC,
8.) 12.6 VDC,

These are selected via a rotary switch into a LM339 comparator for a "CUTOFF" action when actual input voltage drops below the selected value, so must be accurate (+/-5%).

It's been so long since I've done this (over 20 years) so forgotten all the formulas to make this. Know the values between points, due to consistant 0.2 voltage increase will be the same, but have no way to determine the top and bottom resistor values at this time. Would like the ends to be between 10-50K and the middle one a common resistor value like 2K.

I'm running KiCAD Suite on Kubuntu Linux, if that helps. It's supposed to have a sim package, but do not think it installed correctly!

Cheers!
TBNK
 
Last edited:

TBotNik

New Member
I set my .2 v-drop resistors at 2K, then using E = I x R, I created a speadsheet to calc the other values.

Tried to post here, but virus in the upload code prohibits my machine from participating as my security blocks 100% of all viruses and keytrackers.

Therefore sent to pasteBin at:

http://pastebin.com/6fMw1d32

Turns out the top resistor must be 24K and the bottom 12K.

Cheers!

TBNK

PS

Seems the .pdf version of the file did upload, inspite of telling me it did not!
 

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MikeMl

Well-Known Member
Most Helpful Member
Minor nit

We talk about current flowing through resistors, and voltage (drops) across resistors...
 

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