Basics calculator
Voltage divider
Two resistors share the voltage by their sizes; a load steals from the bottom one.
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The example, worked out
Given
- I want
- What it gives
- Input Vin
- 12 V
- R1 (top)
- 10 kΩ
- R2 (bottom)
- 4.7 kΩ
Working
- no load
- what the output looks like from outside
Results
The formulas
- Vout = Vin × R2 / (R1 + R2)the bottom resistor over the sum
- Rth = R1 ∥ R2what a load sees: keep it a hundred times smaller than the load
The usual traps
- A load near R2 pulls the output down by tens of percent.
- Very large resistors save current but pick up noise and are loaded by an ADC input.
Questions
How do I calculate the output of a voltage divider?
Vout = Vin × R2 / (R1 + R2): the bottom resistor over the sum. Rth = R1 ∥ R2: what a load sees: keep it a hundred times smaller than the load.
What does it give for typical values?
3.84 V from 12 V with 10 kΩ / 4.7 kΩ. Output, no load: 3.84 V.
What are the usual mistakes?
A load near R2 pulls the output down by tens of percent. Very large resistors save current but pick up noise and are loaded by an ADC input.
In the app
Your circuit, drawn live
Change a value: the schematic redraws with your numbers on the parts.
The part you can buy
Results rounded to standard values (E12, E24, E96) and power ratings.
The working, shown
Every step written out. Try it first by hand, then check.
Into your notebook
One click puts the circuit on a sheet of your project.
Open the calculatorOpens in the app on 1 December, with Circuit Notebook 1.0
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