Voltage Divider Equation
A voltage divider is a simple linear circuit that produces an output voltage that is a fraction of its input voltage. Voltage division is the result of distributing the input voltage among the components of the divider.
Frequently Asked Questions
The output voltage is the input voltage multiplied by the ratio of the output resistor to the total resistance: Vout = Vin * (R2 / (R1 + R2)).
A voltage divider is a simple circuit of two series resistors that produces an output voltage which is a fraction of the input voltage. The output is taken from the junction between the two resistors. Formula: Vout = Vin × R2 / (R1 + R2). It is one of the most fundamental circuits in electronics.
Voltage dividers are used to: create reference voltages for ADC inputs on microcontrollers; level-shift signals (e.g., 5V to 3.3V logic); bias transistors and op-amps to their correct DC operating point; reduce sensor output voltages to ADC-compatible levels; and create DC operating points in audio amplifiers.
A voltage divider is only accurate when the load resistance is much larger than R2 (at least 10× greater). When a load is connected in parallel with R2, it reduces the effective resistance and pulls the output voltage lower than calculated. For driving loads, use a voltage regulator IC or op-amp buffer following the divider.
Choose values so that: (1) the ratio R2/(R1+R2) equals your desired voltage fraction; (2) the total resistance is low enough to supply sufficient current to the load, yet high enough to avoid excessive quiescent power loss. A practical guideline is to make the divider current 10 times the expected load current to maintain regulation.
The loading effect reduces the output voltage when a load (RL) is connected in parallel with R2. Actual loaded output: Vout = Vin × (R2‖RL) / (R1 + R2‖RL), where R2‖RL = (R2 × RL)/(R2 + RL). The output drops significantly when RL approaches R2 in value. Keeping R1 and R2 small relative to RL minimises this effect.