Information about External Electric Load
If an electric circuit has a well-defined output terminal, the circuit connected to this terminal (or its input impedance) is the load. (The term 'load' may also refer to the power consumed by a circuit; that topic is not discussed here.)
Load affects the performance of circuits that output voltages or currents, such as sensors, voltage sources, and amplifiers. A household's power outlets provide an easy example: they are a voltage source, outputting 120 V AC, with the household's appliances collectively making up the load. When a power-hungry appliance switches on, it dramatically reduces the load impedance, causing the output voltage to drop. This drop is easily observed; for instance, turning on a vacuum cleaner dims the lights.
When discussing the effect of load on a circuit, it is helpful to disregard the circuit's actual design and consider only the Thévenin equivalent. (The Norton equivalent works just as well, but this discussion will use the Thévenin form.) The Thévenin equivalent of a circuit looks like this:
With no load (open-circuited terminals), all of
falls across the output; the output voltage is . However, the circuit will behave differently if a load is added. We would like to ignore the details of the load circuit, as we did for the power supply, and represent it as simply as possible. If we use an input resistance to represent the load, the complete circuit looks like this:
Whereas the voltage source by itself was an open circuit, adding the load makes a closed circuit and allows current to flow. This current places a voltage drop across
, so the voltage at the output terminal is no longer . The output voltage can be determined by the voltage division rule:
Load affects the performance of circuits that output voltages or currents, such as sensors, voltage sources, and amplifiers. A household's power outlets provide an easy example: they are a voltage source, outputting 120 V AC, with the household's appliances collectively making up the load. When a power-hungry appliance switches on, it dramatically reduces the load impedance, causing the output voltage to drop. This drop is easily observed; for instance, turning on a vacuum cleaner dims the lights.
A more technical approach
(Two sidenotes on generality, for advanced readers. This discussion will disregard nonlinearity. It will also use simple resistances, but they can be readily generalized to impedances for AC analysis.)When discussing the effect of load on a circuit, it is helpful to disregard the circuit's actual design and consider only the Thévenin equivalent. (The Norton equivalent works just as well, but this discussion will use the Thévenin form.) The Thévenin equivalent of a circuit looks like this:
)
The circuit is represented by an ideal voltage source Vs in series with an internal resistance Rs.
With no load (open-circuited terminals), all of
falls across the output; the output voltage is . However, the circuit will behave differently if a load is added. We would like to ignore the details of the load circuit, as we did for the power supply, and represent it as simply as possible. If we use an input resistance to represent the load, the complete circuit looks like this:
)
The input resistance of the load stands in series with Rs.
Whereas the voltage source by itself was an open circuit, adding the load makes a closed circuit and allows current to flow. This current places a voltage drop across
, so the voltage at the output terminal is no longer . The output voltage can be determined by the voltage division rule:
References
See also
electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches.
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The input impedance, load impedance, or external impedance of a circuit or electronic device is the Thévenin equivalent impedance looking into its input.
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In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time.
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volt (symbol: V) is the SI derived unit of electric potential difference or electromotive force.[1][2] It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first modern chemical battery.
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Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second.
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Definition
The amount of electric current (measured in amperes) through some surface, e.g...... Click the link for more information.
sensor is a type of transducer. Direct-indicating sensors, for example, a mercury thermometer, are human-readable. Other sensors, such as a thermocouple, only produce an output voltage or other electrical output which must be interpreted by another device (such as a computer).
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A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force.
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amplifier is any device that will use a small amount of energy and convert it to a larger amount of energy. In popular use, the term today usually refers to an electronic amplifier, often as in audio applications.
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Domestic power plugs and sockets are devices that connect the home appliances and portable light fixtures commonly used in homes to the commercial power supply so that electric power can flow to them.
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volt (symbol: V) is the SI derived unit of electric potential difference or electromotive force.[1][2] It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first modern chemical battery.
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alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of
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Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal alternating current (AC). Electrical impedance extends the concept of resistance to AC circuits, describing not only the relative magnitudes of the voltage and current, but also the
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vacuum cleaner (in colloquial British English also hoover[1]) is a device that uses an air pump to create a partial vacuum to suck up dust and dirt, usually from carpeted floors, but also from tiled floors and other smooth surfaces.
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nonlinear system is a system which is not linear i.e. a system which does not satisfy the superposition principle. Less technically, a nonlinear system is any problem where the variable(s) to be solved for cannot be written as a linear sum of independent components.
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Electrical resistance is a measure of the degree to which an object opposes an electric current through it. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens.
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In electrical circuit theory, Thévenin's theorem for linear electrical networks states that any combination of voltage sources, current sources and resistors with two terminals is electrically equivalent to a single voltage source V and a single series resistor R.
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Norton's theorem for electrical networks states that any collection of voltage sources, current sources, and resistors with two terminals is electrically equivalent to an ideal current source, I, in parallel with a single resistor, R.
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The input impedance, load impedance, or external impedance of a circuit or electronic device is the Thévenin equivalent impedance looking into its input.
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The term Open circuit may refer to:
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- Open-circuit voltage, the difference of electrical potential between two terminals of a device when there is no external load connected
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closed-circuit can refer to:
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- closed-circuit television.
- rebreather breathing sets.
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In electronics, a voltage divider is a simple device designed to create a voltage (Vout) which is proportional to another voltage (Vin).
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dummy load is a device used to simulate an electrical load, usually for testing purposes.
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Radio
In radio this device is also known as a dummy antenna or a radio frequency termination...... Click the link for more information.
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