Voltage Divider Calculator
Calculate output voltage from a resistive voltage divider. Enter input voltage and two resistor values. Optionally include load resistance to see loading effects.
What is the voltage divider formula?
The voltage divider formula is V_out = V_in × (R₂/(R₁ + R₂)), where V_in is input voltage, R₁ is the resistor from V_in to V_out, and R₂ is the resistor from V_out to ground. The output voltage is proportional to the ratio of R₂ to total resistance.
How does a voltage divider work?
A voltage divider uses two resistors in series to create a lower voltage from a higher voltage source. Current flows through both resistors, creating voltage drops. The voltage at the junction point (between resistors) is the divided voltage, determined by the resistor ratio.
Why does loading affect voltage divider output?
When you connect a load (resistance) to the output, it appears in parallel with R₂, reducing effective resistance and lowering output voltage. For accurate voltage division, load resistance should be at least 10× higher than R₂. Use R_load in calculations for precision.
How do I choose resistor values for a voltage divider?
Balance two factors: 1) Lower resistance wastes more power but handles loads better. 2) Higher resistance saves power but is more affected by loading. Typical total resistance: 10kΩ-100kΩ for sensing, 1kΩ-10kΩ for moderate loads. Ensure power ratings are adequate.
Can I use voltage dividers for power supplies?
Voltage dividers are NOT suitable for power supplies because output voltage drops significantly under load. Use voltage regulators (linear or switching) for power supplies. Voltage dividers are for sensing, biasing, reference voltages, and signal conditioning where current draw is minimal.
What is the output impedance of a voltage divider?
Output impedance Z_out = R₁ || R₂ = (R₁ × R₂)/(R₁ + R₂). This is the Thévenin equivalent resistance. Lower output impedance handles loads better. To minimize loading effects, ensure load resistance >> Z_out (at least 10× larger).
How much power does a voltage divider dissipate?
Total power P = V_in² / (R₁ + R₂). Power is wasted as heat in both resistors. P₁ = I² × R₁ and P₂ = I² × R₂, where I = V_in/(R₁ + R₂). Higher resistance values reduce power waste but increase output impedance. Choose resistor power ratings accordingly.
What are common voltage divider applications?
Applications: sensor signal conditioning (potentiometers, thermistors), reference voltages for comparators, ADC input scaling, biasing transistors and op-amps, battery voltage monitoring, logic level shifting (with care), and resistive touch sensors. Not for powering circuits with significant current draw.
Can I use capacitors in a voltage divider?
Yes, capacitive voltage dividers work for AC signals. The formula is similar: V_out = V_in × (C₁/(C₁ + C₂)), but note C₁ and C₂ positions are swapped compared to resistive dividers. Used in AC applications, touch sensing, and high-voltage measurement. Frequency-dependent.
How do I calculate loaded voltage divider output?
With load R_L across output: 1) Calculate R₂_effective = R₂ || R_L = (R₂ × R_L)/(R₂ + R_L). 2) Use V_out = V_in × (R₂_effective/(R₁ + R₂_effective)). The load appears in parallel with R₂, reducing effective R₂ and lowering output voltage.
What happens if I swap R₁ and R₂?
Swapping R₁ and R₂ inverts the output. If R₁ > R₂ originally gave V_out < V_in/2, swapping gives V_out > V_in/2. The ratio R₂/(R₁+R₂) determines output fraction. Example: 1kΩ and 3kΩ gives either 0.25× or 0.75× V_in depending on position.
How accurate are voltage dividers?
Accuracy depends on resistor tolerances. For 1% resistors, expect ~2% worst-case error. Use precision resistors (0.1% or better) for accurate references. Temperature coefficients also affect accuracy. For critical applications, use voltage references (like TL431) instead of simple dividers.