Simple Voltage Divider

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When building a circuit, there may come a time when you only need a fraction of the voltage that is in the input.  Dividing this voltage is simple and requires a few basic components.

You are going to need two resistors of the same value, and a battery.  The reason we are using two resistors of the same value is so we will cut the voltage in half.  Later I will describe the equation used to calcuate the resistor values needed to achieve a different output such as 3/4 of the input, or 1/8.

I was inspired to write this instructable because I needed 4.5 volts to charge batteries in a circuit, and I had a rechargable 9v battery.  I used two 1k ohm resistors to dial this down to the 4.5v needed for my project.  It worked perfectly and I still have the circuit now.

As you can see in the picture, I used two 2 ohm resistors, but you can use any value resistors to cut the voltage in half as long as they are equal.

Here is the equation to calculate the Output voltage and the resistor values.

Output Voltage=  r2
r2+r1   x Input Voltage

I hope you enjoyed building a voltage dividing circuit, and questions and comments are appreciated so please post them below!

-Doctordv

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4 Discussions

P=V*I, and for a resistor, V=I*R, because of Ohm's Law, so the power dissipated (as heat) by a resistor is:

P = V*I = I^2*R = V^2/R

That result is general. So if you have some network with a bunch of resistors in it, you can calculate the power dissipated by each resistor, provided you know the voltage V across (or current I=V/R through) each resistor.