Voltage Dividers  Online Calculator
Output voltage potential divider.
Voltage dividers are important in electronic circuits and does the opposite of amplifiers. Voltage dividers can be regarded as "deamplifiers". 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 }R_{2 }/ (R_{1} + R_{2}) (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 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 (Voltage) 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
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, 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.
Adjustable Voltage Dividers
Adjustable voltage dividers can be made from fixed and variable resistors or from potentiometers. Other option are long series of (equal) resistors and switch arrangements to toggle between the resistors.
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.
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