Voltage Divider Calculator

Calculate output voltage, current, and power dissipation for 2-resistor voltage divider circuits

Resistor Voltage Divider

Connected between Vin and Vout
Connected between Vout and Ground
Vin 9 V R1 10 kΩ R2 10 kΩ Vout 4.5 V
Output Voltage (Vout) 0.00 V
Total Current (I) 0.00 mA
Power in R1 (P1) 0.00 mW
Power in R2 (P2) 0.00 mW

Understanding Voltage Dividers

The Formula

The voltage divider rule allows you to calculate the output voltage across one of the resistors in a series circuit.

Vout = Vin × [ R2 / (R1 + R2) ]

Where:

  • Vin: Input voltage
  • R1: Resistor connected to Vin
  • R2: Resistor connected to Ground

Real-World Applications

  • Level Shifting: Converting 5V logic signals to 3.3V for microcontrollers (like Arduino or ESP32).
  • Sensor Reading: Creating a voltage that changes with a variable resistor (potentiometer, thermistor, or photoresistor) so an ADC can read it.
  • Reference Voltages: Providing a stable reference voltage for comparators or op-amps.
  • Biasing: Setting the DC operating point of transistors in amplifier circuits.

Important Considerations

  • Load Impedance: If you connect a load to Vout, it acts in parallel with R2, lowering the effective resistance and dropping Vout. Voltage dividers are best for high-impedance loads (like microcontroller ADC inputs).
  • Power Dissipation: Resistors convert electrical energy into heat. Always check that the power dissipated (P = V²/R or I²R) is well below the resistor's wattage rating (usually 1/4W or 0.25W).
  • Efficiency: Voltage dividers are inefficient for power delivery because current constantly flows through both resistors to ground, wasting power.

Pro Design Tips

  1. Choose resistor values in the 1kΩ to 100kΩ range. Too low wastes power; too high makes the circuit susceptible to noise and loading effects.
  2. Use 1% tolerance resistors (E96 series) if you need precise output voltages.
  3. If driving a low-impedance load, use a voltage regulator or an op-amp buffer instead of a simple resistor divider.

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