- Bridge circuit
A

**bridge circuit**is a type ofelectrical circuit in which the current in a conductor splits into two parallel paths and then recombines into a single conductor, thereby enclosing a loop. It was originally used for measurement purposes, but can also be used in power supplies.The best-known bridge circuit, the

Wheatstone bridge , was invented bySamuel Hunter Christie and popularized byCharles Wheatstone , and is used for measuring resistance. It is constructed from four resistors, one of which has an unknown value (R_{x}), one of which is variable (R_{2}), and two of which are fixed and equal (R_{1}and R_{3}), connected as the sides of a square. Two opposite corners of the square are connected to a source of electrical current, such as a battery. Agalvanometer is connected across the other two opposite corners. The variable resistor is adjusted until the galvanometer reads zero. It is then known that the ratio between the variable resistor and its neighbour is equal to the ratio between the unknown resistor and its neighbour, and this enables the value of the unknown resistor to be calculated.The Wheatstone bridge has also been developed to measure impedance in AC circuits, resulting in designs such as the

Wien bridge , theMaxwell bridge and theHeaviside bridge . All are based on the same principle, which is to compare the output of twopotentiometer s sharing a common source.In power supply design, a bridge circuit or

bridge rectifier is an arrangement ofdiode s or similar devices used to rectify an electric current, i.e. to convert it from an unknown or alternating polarity to a direct current of known polarity.In some

motor controller s, aH-bridge is used to control the direction the motor turns.**See also***

Fontana bridge

*Graetz bridge

*Kelvin bridge

*Lattice filter

*Maxwell bridge

*Phantom circuit - a use of balanced bridge circuits

*Wheatstone bridge

*Wien bridge oscillator

*Bridge T circuit **External links*** [

*http://www.allaboutcircuits.com/vol_1/chpt_8/10.html Bridge circuits*] - Chapter 8 from an online book.

* [*http://www.ecelab.com/bridge-circuits.htm Wien, Shering, Hay, Owen, Maxwell, and Resonance Bridges*] - With balance equations

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