Divisor de tensão Vout

Voltage divider: computing Vout from Vin, R1 and R2

A voltage divider is just two resistors in series, with the output read across R₂: Vout = Vin · R₂ / (R₁ + R₂). Example: V_in = 9 V with R₁ = 1 kΩ, R₂ = 2.2 kΩ gives V_out = 9 · 2.2 / 3.2 ≈ 6.19 V, and the current through the chain is I = V_in / (R₁ + R₂). Critical caveat: the moment the next stage draws current from V_out, the output shifts. To stay stable, the divider should source at least 10× the load current. When the load is high-impedance, drop an op-amp voltage follower (a unity-gain buffer) right after the divider.

Applications: ADC reads, logic-level shift, references

If you want to read a resistive sensor (LDR, NTC thermistor, potentiometer) into an MCU ADC (Arduino 0–5 V, ESP32 0–3.3 V), a divider is usually the first thing you reach for. The same circuit level-shifts a 5 V signal down to 3.3 V (say, Arduino TX → ESP32 RX with R₁ = 1 kΩ, R₂ = 2 kΩ), gives you a simple voltage reference, and works as a passive audio attenuator in line-level circuits.

FAQ

Why does V_out drop under load? The load resistance sits in parallel with R₂, which lowers the effective bottom resistance and throws off the divider ratio.

Can I power a circuit with a divider? Only if the load is in the microamp range. For anything that draws real power, reach for a linear regulator (LDO) or a buck converter, since a divider just burns power as heat and sags badly.

What resistor values should I pick? For MCU sensor reads, 1–100 kΩ is the usual range. Go too low and you waste current; go too high and the divider gets noise-sensitive and starts depending on the load.