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All devices and connections have non-zero resistance and reactance, and therefore no device can be a perfect source. The output impedance is often used to model the source's response to current flow. Some portion of the device's measured output impedance may not physically exist within the device;
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is lower than when there is no current delivered by the cell. The reason for this is that part of the available energy of the cell is used up to drive charges through the cell. This energy is wasted by the so-called "internal resistance" of that cell. This wasted energy shows up as lost voltage.
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The actual output impedance for most devices is not the same as the rated output impedance. A power amplifier may have a rated impedance of 8 ohms, but the actual output impedance will vary depending on circuit conditions. The rated output impedance is the impedance into which the amplifier can
201:
Sources are modeled as ideal sources (ideal meaning sources that always keep the desired value) combined with their output impedance. The output impedance is defined as this modeled and/or real impedance in series with an ideal voltage source. Mathematically, current and voltage sources can be
491:. It is impossible to directly measure the internal resistance of a battery, but it can be calculated from current and voltage data measured from a circuit. When a load is applied to a battery, the internal resistance can be calculated from the following equations:
612:
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The source resistance of a purely resistive device can be experimentally determined by increasingly loading the device until the voltage across the load (AC or DC) is one half of the open circuit voltage. At this point, the load resistance and
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The generalized source impedance for a reactive (inductive or capacitive) source device is more complicated to determine, and is usually measured with specialized instruments, rather than taking many measurements by hand.
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some are artifacts that are due to the chemical, thermodynamic, or mechanical properties of the source. This impedance can be imagined as an impedance in series with an ideal
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when the load draws current, the source network being the portion of the network that transmits and the load network being the portion of the network that consumes.
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245:. (The internal resistance may not be the same for different types of loading or at different frequencies, especially in devices like chemical batteries.)
419:, the input impedance of components is several times (technically, more than 10) the output impedance of the device connected to them. This is called
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Internal resistance varies with the age of a battery, but for most commercial batteries the internal resistance is on the order of 1 ohm.
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It can more accurately be described by keeping track of the voltage vs current curves for various loads, and calculating the resistance from
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57:
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Circuit to the left of central set of open circles models the source circuit, while circuit to the right models the connected circuit.
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607:{\displaystyle {\begin{aligned}R_{B}&=\left({\frac {Vs}{I}}\right)-R_{L}\\&={\frac {V_{S}-V_{L}}{I}}\end{aligned}}}
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195:
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221:, the term "output impedance" usually refers to the effect upon a small-amplitude signal, and will vary with the
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gives the small source impedance (output impedance) of the power amplifier. This can be calculated from the
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is a concept that helps model the electrical consequences of the complex chemical reactions inside a
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is usually less than 0.1 Ω, but this is rarely specified. Instead it is "hidden" within the
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In video, RF, and other systems, impedances of inputs and outputs are the same. This is called
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of the transistor, that is, with the direct current (DC) and voltage applied to the device.
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of the loudspeaker (typically 2, 4, or 8 ohms) and the given value of the damping factor.
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Measure of the opposition to current flow by an internal electrical load
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Calculation of the
Damping Factor and the Damping of Impedance Bridging
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Because of this the output impedance is sometimes referred to as the
149:
132:. The output impedance is a measure of the source's propensity to
416:
395:{\displaystyle Z_{\mathrm {S} }={\frac {Z_{\mathrm {L} }}{DF}}}
326:{\displaystyle DF={\frac {Z_{\mathrm {L} }}{Z_{\mathrm {S} }}}}
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When there is a current through a cell, the measured
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deliver its maximum amount of power without failing.
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882:(2nd ed.). Merrill. pp. 243–246.
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172:is input impedance as seen by the source.
80:Learn how and when to remove this message
43:This article includes a list of general
809:{\displaystyle r={\frac {E-V_{L}}{I}}}
734:is the total resistance of the circuit
676:is the battery voltage without a load
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104:is the measure of the opposition to
879:Fundamentals of Electronic Devices
705:is the battery voltage with a load
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49:it lacks sufficient corresponding
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851:Early effect small-signal model
186:, or in parallel with an ideal
926:Audio amplifier specifications
202:converted to each other using
1:
856:Equivalent series resistance
264:The real output impedance (Z
196:Series and parallel circuits
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451:or a matched connection.
124:being connected that is
768:Internal resistance is
415:Generally in audio and
64:more precise citations.
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94:electrical engineering
931:Electrical parameters
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727:{\displaystyle R_{L}}
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698:{\displaystyle V_{L}}
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669:{\displaystyle V_{S}}
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640:{\displaystyle R_{B}}
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204:Thévenin's theorem
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889:978-0-675-08771-1
836:Nominal impedance
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749:{\displaystyle I}
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213:In the case of a
130:electrical source
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18:Output resistance
16:(Redirected from
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876:(1975). "11".
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893:. Retrieved
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472:= 1/1 = 1 .
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336:Solving for
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238:are equal.
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217:, such as a
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122:load network
120:), into the
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229:Measurement
177:Description
62:introducing
920:Categories
895:27 October
867:References
861:Power gain
223:bias point
219:transistor
114:resistance
70:April 2023
45:references
788:−
582:−
546:−
480:Batteries
433:>>
243:Ohm's law
118:reactance
110:impedance
820:See also
444:> 10
126:internal
489:battery
268:) of a
128:to the
106:current
58:improve
886:
765:e.m.f.
617:where
108:flow (
100:of an
96:, the
47:, but
897:2011
884:ISBN
417:hifi
206:and
198:).
194::
192:see
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