This is probably very simple but my brain won't get around it.

How do I calculate resistor values in a voltage divider circuit as follows:

Vin = 255V
R1 = unknown
Vout after R1 = 195V
R2 = unknown
Vout after R2 = 150V
R3 = 10K ohms
Vout after R3 = 0V

What are the steps for calculating R1 and R2?

Many thanks
Mike

 

It is all a matter of proportion, involving fractions.

Show a schematic to work with would help, otherwise too many assumptions creep in.

 

Hi Bill,

thanks for the reply. I don't have the tools to draw a schematic. However it is a series circuit and the order of the items as set out in my original post is the order that they appear in the circuit.

Regards
Mike

 

Hello,

Here is a drawing made in paint:

The current can be calculated using the voltage drop of R3 and the given value.
With this current you can calculate the other resistors.

Bertus

 

Take a look at my blog. I offer a set of templates under the name of PaintCAD that will work for any graphics program (I use MS Paint), along with a fairly extensive cookbook of drawings made with this package.

Bill's Index

Introduction and PaintCAD

I am one of this sites graphic artists.

 

Thanks to both of you for your assistance. My answers so far from that are:

Circuit Current: 15mA
R2: 3 K ohms
R1: 4 K ohms


Does that sound right?

Many thanks
Mike

 

Hello,

You are correct.
By making use of Ohms law the answers where calculated correctly.

Bertus

 

Your answers are the same as those that I calculated.

hgmjr

 

Many thanks to all of the people who assisted.

No doubt I'll have other questions -

Mike

 

Hello,

Good to hear you are helped well.

If you have any questions, start asking.
We will be happy to helping you answering the questions.

There is also the eBook, see the tabs on the top of the page.
Did you also look at the useful websites thread:
http://forum.allaboutcircuits.com/showthread.php?t=9538
Or the RF related links thread:
http://forum.allaboutcircuits.com/sh...ad.php?t=2201

Bertus