Voltage Divider Calculator
Compute the output voltage of a voltage divider (Vout = Vin × R2 / (R1+R2)) and find resistor values for a desired output. Everything in your browser.
Fórmula: Vout = Vin × R2 / (R1 + R2). Corrente: I = Vin/(R1+R2). Atenção: divisor sem buffer cai sob carga.
Voltage divider: scaling Vin with two resistors
A voltage divider uses two resistors in series to produce an output voltage that is a fraction of the input: Vout = Vin · R₂ / (R₁ + R₂), measured across R₂. Example: Vin = 5 V with R₁ = R₂ = 10 kΩ gives Vout = 2.5 V. The divider current is I = Vin / (R₁ + R₂), and total power is P = Vin · I. Critical limitation: a bare divider (no op-amp buffer) is loaded by the next stage — any current pulled from Vout changes the output voltage. Rule of thumb: the divider current should be at least 10× the load current to keep Vout "stiff". For high-impedance loads use a unity-gain op-amp (voltage follower) after the divider.
Applications: sensors, logic level shifting, references
Voltage dividers read resistive sensors (LDR, NTC, potentiometer) into an MCU analog input (0–5 V on Arduino, 0–3.3 V on ESP32). They shift logic levels down — for example, scaling a 5 V Arduino TX to 3.3 V for an ESP32 RX using R₁ = 1 kΩ, R₂ = 2 kΩ. They also create simple voltage references and biasing networks in amplifier stages.
FAQ
Why does my Vout drop when I connect a load? The load is in parallel with R₂, lowering the effective bottom resistance and shifting the ratio. Either use lower-value resistors (more divider current) or buffer with an op-amp.
Can I use it to power a circuit? Only for very low-current loads (microamps). For real power use a regulator (LDO, buck converter), not a divider.
What resistor values should I pick? Trade-off: small values waste power (high quiescent current), large values are sensitive to loading and noise. For MCU sensor reads, 1–100 kΩ is typical.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.