Voltage Divider

This circuit is so useful in electronics that it has its own name, a Voltage Divider. A voltage divider is used to divide a large voltage into smaller voltages. When designing a voltage divider, you do not have to do all of the math that we did above, there is a short cut. First we have to name a couple of points appropriately.

• The battery is called Vin (for Input Voltage)
• The voltage at point B is called Vout (for Output Voltage)

The point of a voltage divider is to create a new Vout based on a given Vin. Here is the generic circuit.

We can generalize the solution for the value of Vout using the following equation.

Lets break this down. Vout is equal to Vin times everything in the parenthesis. The value in the parenthesis is the ratio of the bottom resistor to the sum of the two resistors. Using the example above:

We start by plugging in the values we know.

Now add 80 and 20 together to get 100.

20 divided by 100 is .2.

Finally multiply 10 times .2 to get the answer, 2 volts.

The answer of 2 Volts is exactly the same as the answer we got by using Ohms Law above. In fact, the Voltage Divider equation is created by using algegra to rearrange the equations on the previous page into one big equation. The answers will always be the same. You can use which ever method you like better.

Conclusion

Resistors in series will show up many times in electronics. When resistors are in series, the current through both resistors is the same. Each resistor will drop voltage as the current passes through it. We use this voltage drop to create new voltages with a circuit known as a voltage divider. With these techniques you are able to create any voltage that you need in your project, as long as Vout is less than Vin.