Meaning and mechanism
The voltage divider is a circuit that extracts a portion of the voltage from a series resistor. The output is the voltage across one of the resistors, and in the absence of a load, the same current flows through both resistors.
If a load is added to the output, it forms a parallel connection with the lower resistance and the load. This can result in a smaller effective resistance, which may be lower than the original no-load output.
Relationships and conditions
Under no load, it is Vout=VinR₂/(R₁+R₂). When a load RL is present, instead of R₂, we use R₂∥RL for calculation. The position of the variable resistor is replaced by the ratio of the two resistors.
A sufficiently large resistance is required to use the no-load circuit approximately. Unlike a power supply that maintains a constant output even when the load changes significantly, a voltage divider does not.
What to observe in the simulation
Without a load, Vout = αVin. Connecting a load lowers the output voltage.
The ideal potentiometer has a total resistance of 10 kΩ. Position is limited to 5–95% to avoid a short at the endpoints. The voltmeter has infinite resistance. Use this simulation; do not reproduce it with real power supplies or wall outlets.
Key relationships and symbols
R₂ = αR · Vout = Vin(R₂ ∥ RL)/(R₁ + R₂ ∥ RL)
| Symbol | Meaning | Unit |
|---|---|---|
| R₁, R₂ | Upper and lower divider resistances | Ω |
| RL | Load resistance connected to the output | Ω |
| Vout | Output voltage | V |
Worked example
What is the output with 6 V input, a 50% wiper position and a 10 kΩ load?
2.4 V
Common misconceptions
- The output voltage can vary, even when using the same variable resistor position, depending on the load that is connected.