Potential Divider  Online Calculator
Output voltage with a potential divider.
A potential divider is the simplest way of producing a source of lower e.m.f. from a source of higher e.m.f.
The output voltage from a potential divider can be calculated as
U_{out} = U_{in }R_{2 }/ (R_{1} + R_{2}) (1)
where
U_{out} = output voltage (V)
R = resistance (Ohms, Ω)
U_{in} = input voltage (V)
Example  Potential Divider  High Power Consumption
The output voltage from a potential divider with two resistors R_{1} = 10 ohms and R_{2} = 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 R_{1} and R_{2} (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 Divider  Lower Power Consumption
The output voltage from a potential divider with two resistors R_{1} = 1000 ohms and R_{2} = 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 R_{1} and R_{2} (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 R_{1} (ohm)
resistor R_{2} (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 abocve are for U_{in} = 12 V, R_{2} = 47 ohm and U_{out} = 3.3 V. Since the sum of the resistances (R_{1} + R_{2}) according the nomogram is approximately 170 ohm  the resistance R_{1} can be calculated as
R_{1} ≈ (170 ohm  47 ohm)
≈ 123 ohm.
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