# circuit divider

Discussion in 'Homework Help' started by learjet, Jan 27, 2008.

1. ### learjet Thread Starter New Member

Jan 27, 2008
1
0
I jest started on circuit dividers and id there a best way or forumla that calculates circuit dividers my professor does not do it easy....if you can help that would be great.

Thanks all
Mike

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Do you mean voltage dividers? If so the sum of the resistances gives you Rt. Current is given by Ohm's law, I = E/R. That current is common to all the resistors, so the drop across any of them also follows from Ohm's law, E = IR.

3. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Voltage will be proportional to resistance. For a two resistor divider, Er1/(Er1+Er2) = R1/(R1+R2).

Here's an example: If we have a 90Vrms(max) sine wave we need to sample, and our circuit can safely accept 6Vrms(max), we know 6/90 = 6/(6+84). This tells us the ratio between the two resistors will be 6:84 = 1:14. We can then pick through standard resistor values and choose two with roughly a 1:14 ratio. 1.4M and 10K both at 1% would do nicely for this example.

Another example: We find a divider with a 137K R1 in series with a 221K R2. Applied voltage across the divider is 12Vdc. Since, Er1=(Er1+Er2)*R1/(R1+R2), divider output = 12*137/(137+221) = 4.59Vdc

4. ### hgmjr Moderator

Jan 28, 2005
9,030
214
For more information, take a look at the material in the AAC ebook on the topic of Voltage dividers.

hgmjr