A voltage divider consists of the two resistances R1 and R2 connected in series across the supply voltage Vs. The supply voltage is divided between the two resistances to give an output voltage Vo which is the voltage across R2. An important use of the voltage dividers is to connect input transducers to circuits.
The output voltage Vo depends on the size of R2 relative to R1:
- If R2 is much smallerthan R1, Vo is small
(low, almost 0V) because most of the voltage is across R1.
- If R2 is about the sameas R1, Vo is about half Vs
because the voltage is shared about equally between R1 and R2.
- If R2 is much largerthan R1, Vo is large
(high, almost Vs) because most of the voltage is across R2.
If you need a precise value for the output voltage Vo you can use this formula:
Voltage divider output,[pmath] Vo = Vs*R2 /( R1 + R2)[/pmath]
Note: this formula and the rough rules given above assume that the negligible current flows from the output. This is true if Vo is the connected to a device with a high resistance such as voltmeter or an IC input. For further information please see the page on the impedance. If the output is connected to a transistor Vo cannot become much greater than 0.7V because the transistor’s base emitter junction behaves like a diode.
Voltage dividers are also known as potential dividers, a name which comes from potential difference (the proper name for voltage).