Voltage Dividers - Online Calculator

Voltage dividers are important in electronic circuits and does the opposite of amplifiers. Voltage dividers can be regarded as "de-amplifiers". A potential voltage divider is the simplest way of producing a source of lower e.m.f. (voltage) from a source of higher e.m.f. (voltage).

The output voltage from a potential divider can be calculated as

U_out = U_in R₂ / (R₁ + R₂)                 (1)

where

U_out = output voltage (V)

R = resistance (Ohms, Ω)

U_in = input voltage (V)

Example - Potential (Voltage) Divider - High Power Consumption

The output voltage from a potential divider with two resistors R₁ = 10 ohms and R₂ = 20 ohms and input voltage 12 V can be calculated as

     U_out = (12 V) (20 Ω) / ((10 Ω) + (20 Ω))

        = 8 (V)

The current through the potential divider R₁ and R₂ (ex. output current) can be calculated by using Ohm's law

I = U / R

  = (12 V) / ((10 Ω) + (20 Ω))

  = 0.4 A

The power consumption of the divider can be calculated

P = U I

   = (12 V) (0.4 A)

   = 4.8 W

Example - Potential (Voltage) Divider - Lower Power Consumption

The output voltage from a potential divider with two resistors R₁ = 1000 ohms and R₂ = 2000 ohms and input voltage 12 V can be calculated as

     U_out = (12 V) (2000 Ω) / ((1000 Ω) + (2000 Ω))

        = 8 (V)

The current through the potential divider R₁ and R₂ (ex. output current) can be calculated by using Ohm's law

I = U / R

  = (12 V) / ((1000 Ω) + (2000 Ω))

  = 0.004 A

The power consumption of the divider can be calculated

P = U I

   = (12 V) (0.004 A)

   = 0.048 W

The power consumption in a potential divider can be reduced by increased resistance.

Potential Divider - Calculator

input voltage U_in (volts)

resistor R₁ (ohm)

resistor R₂ (ohm)

Potential Divider Nomogram

The nomogram below can be used to estimate a potential divider.

  Download and print the Potential Divider Nomogram!

The default values in the nomogram above are for U_in = 12 V, R₂ = 47 ohm and U_out = 3.3 V. Since the sum of the resistances (R₁ + R₂) according the nomogram is approximately 170 ohm - the resistance R₁ can be calculated as

R₁ ≈ (170 ohm - 47 ohm)

    ≈ 123 ohm.

Adjustable Voltage Dividers

Zener Diodes as Voltage Dividers

Note that a Zener diode can be used to create constant voltage inside an electronic circuit simply by providing the diode with a constant current derived from a higher voltage as indicated in the figure. A Zener diode is designed to have a specific breakdown voltage so that it will conduct current in reverse when the cathode reaches its threshold voltage.