From en.wikipedia.org:
[Type of electrical circuit] A BRIDGE CIRCUIT is a topology of electrical
circuitry in which two circuit branches (usually in parallel with each other)
are "bridged" by a third branch connected between the first two branches at
some intermediate point along them. The bridge was originally developed for
laboratory measurement purposes and one of the intermediate bridging points is
often adjustable when so used. Bridge circuits now find many applications,
both linear and non-linear, including in instrumentation, filtering and power
conversion.[1][2]
The best-known bridge circuit, the Wheatstone bridge, was invented by Samuel
Hunter Christie and popularized by Charles Wheatstone, and is used for
measuring resistance. It is constructed from four resistors, two of known
values _R_<sub>1</sub> and _R_<sub>3</sub> (see diagram), one whose resistance
is to be determined _R_<sub>x</sub>, and one which is variable and calibrated
_R_<sub>2</sub>. Two opposite vertices are connected to a source of electric
current, such as a battery, and a galvanometer is connected across the other
two vertices. The variable resistor is adjusted until the galvanometer reads
zero. It is then known that the ratio between the variable resistor and its
neighbour R1 is equal to the ratio between the unknown resistor and its
neighbour R3, which enables the value of the unknown resistor to be
calculated.
The Wheatstone bridge has also been generalised to measure impedance in AC
circuits, and to measure resistance, inductance, capacitance, and dissipation
factor separately. Variants are known as the Wien bridge, Maxwell bridge, and
Heaviside bridge (used to measure the effect of mutual inductance).[3] All are
based on the same principle, which is to compare the output of two potential
dividers sharing a common source.
In power supply design, a bridge circuit or bridge rectifier is an arrangement
of diodes 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 controllers, an H-bridge is used to control the direction the
motor turns.
** Bridge current equation
alt=bridge network current flow From the figure to the right, the bridge
current is represented as _I_<sub>5</sub>
Per Thévenin's theorem, finding the Thévenin equivalent circuit which is
connected to the bridge load _R_<sub>5</sub> and using the arbitrary current
flow _I_<sub>5</sub>, we have:
Thevenin Source (_V_<sub>th</sub>) is given by the formula:
<math>V_{th}=\left(\frac{R_2}{R_1+R_2}-\frac{R_4}{R_3+R_4}\right)\times
U</math>
and the Thevenin resistance (_R_<sub>th</sub>):
<math>R_{th}=\frac{R_1 \times R_2}{R_1+R_2}+\frac{R_3 \times R_4}{R_3 +
R_4}</math>
Therefore, the current flow (_I_<sub>5</sub>) through the bridge is given by
Ohm's law:
<math>I_5=\frac{V_{th}}{R_{th}+R_5}</math>
and the voltage (_V_<sub>5</sub>) across the load (_R_<sub>5</sub>) is given
by the voltage divider formula:
<math>V_5=\frac{R_5}{R_{th} + R_5} \times V_{th}</math>
** See also
- Phantom circuit - a use of balanced bridge circuits in telephony
- Lattice filter - an application of bridge topology to all-pass filters
** Gallery
{{gallery |Image:Wheatstonebridge.svg|Wheatstone bridge |Image:Mostek
Wiena.svg| Wien bridge |Image:Maxwell_bridge.svg| Maxwell bridge
|Image:H_bridge.svg| H bridge |Image:Fontanabridge.png| Fontana bridge
|Image:Diode_bridge_alt_1.svg| Full wave rectifier |Image:KelvinBridge.gif|
Kelvin bridge |Image:Lattice_filter%2C_general.svg| Lattice bridge
|Image:Zobel_%283%29_Bridge_T.svg| Bridged T circuit |Image:Carey Foster
bridge.svg| Carey Foster bridge |Image:Ring_Modulator.PNG| Ring Modulator }}
** References
[Reflist]
** External links
- Jim Williams , "Bridge circuits: Marrying gain and balance" (see https://www.analog.com/en/resources/app-notes/an-43f.html) , Linear Technology Application Note 43, June 1990.
- Bridge circuits (see http://www.allaboutcircuits.com/vol_1/chpt_8/10.html) - Chapter 8 from an online book.
[Bridge circuits]
[Authority control]