A voltage divider is a simple circuit which turns a large voltage into a smaller one. Using just two series resistors and an input voltage, we can create an output voltage that is a fraction of the input.
What happens if I connect a load to Vout?
Connecting a load (like a microcontroller pin or motor) puts a resistor in parallel with R2. This lowers the total resistance of the bottom half, causing Vout to drop. This is called the "Loading Effect".
Can I use this to power a motor or LED?
No. Voltage dividers waste power as heat and voltage drops significantly under load. Use a voltage regulator (LDO) or DC-DC buck converter for power supply applications.
How do I choose R1 and R2 values?
Use values between 1kΩ and 100kΩ. Too low wastes power (I = Vin / (R1+R2)). Too high makes the circuit sensitive to noise and loading effects. 10kΩ is a good starting point.
Can Vin be negative?
Yes. If Vin is negative (e.g. -12V), Vout will also be negative, scaled by the resistor ratio.