Voltage Divider

In late July 2013, the wikileki website is being transferred to the reviseOmatic website. Wikileki will vanish soon afterwards.

This page is already available on the new reviseOmatic site: http://reviseomatic.org/help/e-resistors/Resistors%20-%20Voltage%20Divider.php

GCSE    AS	Resistors :: Resistance :: Colour Codes :: BS1852 :: E24 :: Resistors in Parallel Resistors in Series :: Voltage Divider :: Potentiometer :: LDR :: Thermistor
Use Google to Search This Site        reviseOmatic

Circuit

R1 and R2 form a Voltage Divider. The voltage is divided in the ratio of the resistor values (assuming the current is the same in both resistors). Two or more resistors in series can be used to set a required voltage at a point in a circuit. For example, this could correspond to a threshold voltage at which an alarm should sound the voltage output required from a power supply circuit the volume needed from a radio the speed at which a fan runs. V = Vs R2 / (R1 + R2) where Vs is the supply voltage. V1 / R1 = V2 / R2 or ... V1 / V2 = R1 / R2

Potentiometer

Animation

A potentiometer (pot) is a variable resistor with an adjustable slider. You can think of it as two resistors (one on each side of the slider). The diagram above shows the commonest arrangement. There is another straight version often called a fader. Both types are used as volume and tone controls. They are notorious for being unreliable. Dirt gets into the moving parts and corrosion causes problems. Digital pots are available. These don't suffer from these mechanical problems.

When used for position sensing, potentiometers are classed as input transducers.

Voltage Divider Lab Exercise

Build this voltage divider circuit and measure the voltages at A, B, C, D and E without and with the LED. Note what happens when the potentiometer is adjusted.

CTRL+Click for the Falstad Circuit Simulaton: LED Circuit
In options, check European Resistors and uncheck Conventional Current.
Adjust the slider to alter the Potentiometer setting.