Voltage Divider Calculator
A voltage divider calculator determines the output voltage produced by two resistors connected in series across an input voltage. It is commonly used in basic electronic circuits to obtain a lower voltage from a higher supply voltage.
Voltage Divider Formula
For two resistors, the output voltage is:
Vout = Vin × R2 ÷ (R1 + R2)
Here, Vin is the input voltage, R1 is the upper resistor, and R2 is the lower resistor connected to ground.
How a Voltage Divider Works
When two resistors are connected in series, the input voltage is distributed between them according to their resistance values. The output voltage is measured across R2.
For example, if:
Vin = 12 V
R1 = 10 kΩ
R2 = 10 kΩ
Then:
Vout = 12 × 10 ÷ (10 + 10) = 6 V
The output voltage is therefore 6 V.
Finding a Resistor Value
If the desired output voltage, input voltage, and one resistor are known, the other resistor can be calculated.
To find R2:
R2 = R1 × Vout ÷ (Vin − Vout)
To find R1:
R1 = R2 × (Vin − Vout) ÷ Vout
Voltage Divider Current
The current through the two resistors, assuming no load is connected to the output, is:
I = Vin ÷ (R1 + R2)
For the 12 V example with two 10 kΩ resistors:
I = 12 ÷ 20,000 = 0.0006 A
So the divider current is 0.6 mA.
Voltage Divider Example
| Input | Value |
|---|---|
| Input voltage | 12 V |
| R1 | 10 kΩ |
| R2 | 5 kΩ |
| Output voltage | 4 V |
Using the formula:
Vout = 12 × 5 ÷ (10 + 5) = 4 V
Effect of a Load
The basic voltage divider formula assumes that the output is not significantly loaded. If a load resistor is connected to the output, it effectively appears in parallel with R2, changing the output voltage.
For a loaded divider, calculate the equivalent resistance:
Req = R2RL ÷ (R2 + RL)
Then use Req in place of R2 in the voltage divider formula.
Common Mistakes to Avoid
Make sure R2 is the resistor across which the output voltage is measured. Also use consistent resistance units, such as ohms for both resistors.
Remember that a voltage divider is generally intended for signal or reference voltages rather than supplying substantial load current.
Quick Summary
A voltage divider uses two series resistors to reduce an input voltage. The basic output formula is Vout = Vin × R2 ÷ (R1 + R2). The actual output can change when a load is connected to the divider.