Voltage Divider
What is a Voltage Divider?
Definition
A voltage divider is an electrical circuit whose output voltage is smaller than its input (Figure 1).
Figure 1. Voltage Divider Circuit.
The term “voltage divider” relates to how the circuit works. It comprises two series resistors (R1 and R2) and an input voltage source (Vin) as shown in Figure 1. As determined by Ohm’s Law, the output voltage is ‘divided’ down by the ratio of the two series resistors according to the following formula:
A voltage divider in which the value of the resistor(s) is variable is called a potentiometer.
Although it a quick and simple way to create a smaller voltage level from a fixed voltage source (e.g. battery), the voltage divider is inefficient for practical use for a number of reasons:
A voltage divider wastes current from the input voltage source to generate the output voltage. An ideal voltage source should only deliver current to the load.
While increasing the size of the resistors will reduce the amount of wasted current, this also increases the output resistance of the circuit meaning not all of the output voltage is transferred to the load. An ideal voltage source should have zero output resistance, so that all of the voltage is transferred to the load.
For practical applications, the output of a voltage divider circuit must first be buffered by another circuit before use or a more efficient type of voltage reference should be chosen.