Voltage Divider

Set a voltage, account for loading, and find a standard resistor pair.

Formulas

Vout = Vin × R2 / (R1 + R2)

Req = R2 ∥ Rload; Vloaded = Vin × Req / (R1 + Req)

Itop = (Vin − Vloaded) / R1; Ibottom = Vloaded / R2

P1 = (Vin − Vloaded)² / R1; P2 = Vloaded² / R2

Ptotal = P1 + P2 + Pload; error = (Vloaded − Vtarget) / |Vtarget| × 100%

Model & assumptions

Divider current is the top-resistor current, including the load when present. Total power includes the load.

E24 suggestions hold the bottom resistor near its entered value and choose the nearest top value, accounting for the load. Tolerances are not modeled.

Example with default inputs

Output voltage

2.16393 V

Loaded output voltage

2.16393 V

Divider current

983.607 µA

Total power

11.8033 mW

Top resistor power

9.67482 mW

Bottom resistor power

2.12846 mW

Error from target

-34.4262 %