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# 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

Uout = Uin R2 / (R1 + R2)                 (1)

where

Uout = output voltage (V)

R = resistance (Ohms, Ω)

Uin = 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

Uout = (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

Uout = (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

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#### Potential Divider Nomogram

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

The default values in the nomogram above are for Uin = 12 VR2 = 47 ohm and Uout3.3 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

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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### Electrical Series Circuits

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### Electromotive Force - e.m.f

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### Kirchhoff's Voltage and Current Laws

Kirchhoff's current and voltage laws.

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