Voltage divider

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In electronics, a voltage divider or resistor divider is a design technique used to create a voltage (V_out) which is proportional to another voltage (V_in).

Resistor divider

Two resistors are connected as shown in Figure 1. The output voltage, V_out is related to V_in as follows:

<math>

V_{out} = \frac{R_2}{R_1+R_2} \cdot V_{in} <math>

As a simple example, if R₁ = R₂ then

<math>

V_{out} = \frac{1}{2} \cdot V_{in} <math>

Any other ratio between 0 and 1 is also possible.

Note that this rule only works if the divider is unloaded, that is, the load resistance is infinite and all of the current flowing through R₁ goes into R₂. If current flows into a load resistance (through V_out), that resistance must be considered in parallel with R₂ (see: resistor) to determine the voltage at V_out.

Figure 1: Resistor Divider

General impedance divider

A voltage divider is usually thought of as two resistors, but capacitors, inductors, or any combined impedance can be used. For general impedances Z₁ and Z₂, the voltage becomes

<math>

V_{out} = \frac{Z_2}{Z_1+Z_2} \cdot V_{in} <math>

For instance, a divider with a resistor and capacitor:

will have voltage ratio:

<math>{V_{out} \over V_{in}} = {{1 \over j \omega C} \over {1 \over j \omega C} + R} = {1 \over 1 + R j \omega C}<math>

since the capacitor's impedance is 1 / jωC (where j is the imaginary number, and ω is frequency in radians per second). The ratio then depends on frequency, in this case decreasing as frequency increases. This circuit is, in fact, a basic lowpass filter, or, in the world of audio, a treble-cut filter.

See also

• Potentiometer
• Wheatstone bridge

External links

• Calculator: voltage divider - loaded and open circuit

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