PROTESHEA / CIRCUIT TOOLS
Voltage divider
calculator.
Two resistors. One useful voltage.
See the output, follow the current, and find out what a load changes.
01 Build your divider
R1 connects to the supply. R2 connects to ground.
Off: an unloaded, high-impedance output.
Output voltage
50% of the input voltage · no load connected
Your voltage divider
Output is measured across R202 See the load effect
A load sits in parallel with R2. It lowers the bottom resistance, so the output magnitude falls.
Bar length = percentage of input voltage magnitude
03 Check each component
Under load, R1 carries the sum of the R2 and load currents.
| Part | Voltage | Current | Power |
|---|
Power is dissipation, not a recommended component rating. Allow headroom and follow temperature derating.
THE MATH, MADE VISIBLE
The bottom resistor
sets the fraction.
Without a load, the same current flows through both resistors. R2 gets its share of the supply voltage.
With a load, first replace R2 with R2 ∥ RL = (R2 × RL) / (R2 + RL). Then use the same divider formula.
Bigger R2, higher output.
For a positive input, increasing the lower resistor raises the output. Increasing the upper resistor lowers it.
A divider is not a regulator.
Use it for sensing or a voltage reference into a suitable high-impedance input. A changing load changes the voltage. Use a regulator or buffer to power a load.
Leave room for the real world.
Resistor tolerance, supply variation and input leakage affect accuracy. ADC sample-and-hold inputs also have settling requirements. Check the device’s input limits and datasheet.
Assumptions, units and limits
This is an ideal DC model with an ideal voltage source and positive, linear resistors. It does not model resistor tolerance, heating, source resistance, AC response or ADC sampling behavior.
Unloaded means no output current is drawn. Turning on the load connects RL from output to ground, in parallel with R2. The output resistance shown is R1 ∥ R2 with the ideal voltage source set to zero and the load disconnected.
Ω = ohms · kΩ = 1,000 Ω · MΩ = 1,000,000 Ω. mV = 0.001 V · kV = 1,000 V. Use a decimal point or scientific notation, such as 4.7 or 1e3. Each resistor must be between 10⁻¹² and 10¹⁵ Ω. Zero-ohm shorts and infinite resistances are not accepted; turn the load off to model an open output.
Input voltage may be positive, negative or zero, with magnitude at most 10⁶ V. Negative results indicate polarity or current opposite the positive-input reference direction. Power is always non-negative. Loading reduction compares voltage magnitudes.
Results use six significant figures. These are educational estimates, not a safety validation. Check actual component ratings, input limits and circuit conditions before building.