Current–voltage characteristic

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The current-voltage characteristics of four devices: a resistor with large resistance, a resistor with small resistance, a P-N junction diode, and a battery with nonzero internal resistance. The horizontal axis represents the voltage drop, the vertical axis the current. All four plots use the passive sign convention. FourIVcurves.svg
The current–voltage characteristics of four devices: a resistor with large resistance, a resistor with small resistance, a P–N junction diode, and a battery with nonzero internal resistance. The horizontal axis represents the voltage drop, the vertical axis the current. All four plots use the passive sign convention.

A current–voltage characteristic or I–V curve (current–voltage curve) is a relationship, typically represented as a chart or graph, between the electric current through a circuit, device, or material, and the corresponding voltage, or potential difference across it.

Chart graphical representation of data

A chart is a graphical representation of data, in which "the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart". A chart can represent tabular numeric data, functions or some kinds of qualitative structure and provides different info.

Electric current flow of electric charge

An electric current is the rate of flow of electric charge past a point or region. An electric current is said to exist when there is a net flow of electric charge through a region. In electric circuits this charge is often carried by electrons moving through a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionized gas (plasma).

Voltage difference in the electric potential between two points in space

Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points. The difference in electric potential between two points in a static electric field is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule per 1 coulomb. The official SI definition for volt uses power and current, where 1 volt = 1 watt per 1 ampere. This definition is equivalent to the more commonly used 'joules per coulomb'. Voltage or electric potential difference is denoted symbolically by V, but more often simply as V, for instance in the context of Ohm's or Kirchhoff's circuit laws.

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In electronics

MOSFET drain current vs. drain-to-source voltage for several values of the overdrive voltage,
V
G
S
-
V
t
h
{\displaystyle V_{GS}-V_{th}}
; the boundary between linear (Ohmic) and saturation (active) modes is indicated by the upward curving parabola. IvsV mosfet.svg
MOSFET drain current vs. drain-to-source voltage for several values of the overdrive voltage, ; the boundary between linear (Ohmic) and saturation (active) modes is indicated by the upward curving parabola.

In electronics, the relationship between the direct current (DC) through an electronic device and the DC voltage across its terminals is called a current–voltage characteristic of the device. Electronic engineers use these charts to determine basic parameters of a device and to model its behavior in an electrical circuit. These characteristics are also known as I–V curves, referring to the standard symbols for current and voltage.

Electronics physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter

Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter.

Direct current Unidirectional flow of electric charge

Direct current (DC) is the unidirectional flow of an electric charge. A battery is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.

Electronic engineering electrical engineering discipline which utilizes nonlinear and active electrical components to design electronic circuits, devices, and their systems

Electronic engineering is an electrical engineering discipline which utilizes nonlinear and active electrical components to design electronic circuits, devices, VLSI devices and their systems. The discipline typically also designs passive electrical components, usually based on printed circuit boards.

In electronic components with more than two terminals, such as vacuum tubes and transistors, the current-voltage relationship at one pair of terminals may depend on the current or voltage on a third terminal. This is usually displayed on a more complex current–voltage graph with multiple curves, each one representing the current-voltage relationship at a different value of current or voltage on the third terminal. [1]

Electronic component basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields

An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components.

Vacuum tube Device that controls electric current between electrodes in an evacuated container

In electronics, a vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Transistor Basic electronics component

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

For example the diagram at right shows a family of I–V curves for a MOSFET as a function of drain voltage with overvoltage (VGS − Vth) as a parameter.

The simplest I–V curve is that of a resistor, which according to Ohm's law exhibits a linear relationship between the applied voltage and the resulting electric current; the current is proportional to the voltage, so the I–V curve is a straight line through the origin with positive slope. The reciprocal of the slope is equal to the resistance.

Resistor Passive electrical component providing electrical resistance

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat, may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements, or as sensing devices for heat, light, humidity, force, or chemical activity.

Ohms law relationship between voltage and current across an ideal resistor

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

Origin (mathematics) point in a Euclidean space used as a reference for geometry of surrounding space

In mathematics, the origin of a Euclidean space is a special point, usually denoted by the letter O, used as a fixed point of reference for the geometry of the surrounding space.

The I–V curve of an electrical component can be measured with an instrument called a curve tracer. The transconductance and Early voltage of a transistor are examples of parameters traditionally measured from the device's I–V curve.

Transconductance, also infrequently called mutual conductance, is the electrical characteristic relating the current through the output of a device to the voltage across the input of a device. Conductance is the reciprocal of resistance.

Types of I–V curves

The shape of an electrical component's characteristic curve reveals much about its operating properties. I–V curves of different devices can be grouped into categories:

The quadrants of the I-V plane. Power sources have curves passing through the red regions. Quadrants of IV plane.svg
The quadrants of the I–V plane. Power sources have curves passing through the red regions.
In contrast, devices with I–V curves which pass through the second or fourth quadrants are active components, power sources, which can produce electric power. Examples are batteries and generators. When it is operating in the second or fourth quadrant, current is forced to flow through the device from the negative to the positive voltage terminal, against the opposing force of the electric field, so the electric charges are gaining potential energy. Thus the device is converting some other form of energy into electric energy.


In electrophysiology

An approximation of the potassium and sodium ion components of a so-called "whole cell" I-V curve of a neuron. Whole cell IV.jpg
An approximation of the potassium and sodium ion components of a so-called "whole cell" I–V curve of a neuron.

While I–V curves are applicable to any electrical system, they find wide use in the field of biological electricity, particularly in the sub-field of electrophysiology. In this case, the voltage refers to the voltage across a biological membrane, a membrane potential, and the current is the flow of charged ions through channels in this membrane. The current is determined by the conductances of these channels.

In the case of ionic current across biological membranes, currents are measured from inside to outside. That is, positive currents, known as "outward current", corresponding to positively charged ions crossing a cell membrane from the inside to the outside, or a negatively charged ion crossing from the outside to the inside. Similarly, currents with a negative value are referred to as "inward current", corresponding to positively charged ions crossing a cell membrane from the outside to the inside, or a negatively charged ion crossing from inside to outside.

The figure to the right shows an V–I curve that is more relevant to the currents in excitable biological membranes (such as a neuronal axon). The blue line shows the V–I relationship for the potassium ion. Note that it is linear, indicating no voltage-dependent gating of the potassium ion channel. The yellow line shows the V–I relationship for the sodium ion. Note that it is not linear, indicating that the sodium ion channel is voltage-dependent. The green line indicates the I–V relationship derived from summing the sodium and potassium currents. This approximates the actual membrane potential and current relationship of a cell containing both types of channel.

See also

Related Research Articles

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Electrical resistance and conductance opposition to the passage of an electric current

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Electrical elements are conceptual abstractions representing idealized electrical components, such as resistors, capacitors, and inductors, used in the analysis of electrical networks. All electrical networks can be analyzed as multiple electrical elements interconnected by wires. Where the elements roughly correspond to real components the representation can be in the form of a schematic diagram or circuit diagram. This is called a lumped-element circuit model. In other cases infinitesimal elements are used to model the network, in a distributed-element model.

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Schmitt trigger

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A network, in the context of electronics, is a collection of interconnected components. Network analysis is the process of finding the voltages across, and the currents through, all network components. There are many techniques for calculating these values. However, for the most part, the techniques assume linear components. Except where stated, the methods described in this article are applicable only to linear network analysis.

Current source electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it; dual of a voltage source

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Gunn diode diode

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Load line (electronics) graphical analysis tool for electronic circuit engineering

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Chuas diode

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Passive sign convention

In electrical engineering, the passive sign convention (PSC) is a sign convention or arbitrary standard rule adopted universally by the electrical engineering community for defining the sign of electric power in an electric circuit. The convention defines electric power flowing out of the circuit into an electrical component as positive, and power flowing into the circuit out of a component as negative. So a passive component which consumes power, such as an appliance or light bulb, will have positive power dissipation, while an active component, a source of power such as an electric generator or battery, will have negative power dissipation. This is the standard definition of power in electric circuits; it is used for example in computer circuit simulation programs such as SPICE.

A comparator is an electronic component that compares two input voltages. Comparators are closely related to operational amplifiers, but a comparator is designed to operate with positive feedback and with its output saturated at one power rail or the other. An op-amp can be pressed into service as a poorly performing comparator if necessary, but its slew rate will be impaired.

References

  1. H. J. van der Bijl (1919). "Theory and Operating Characteristics of the Themionic Amplifier". Proceedings of the IRE. Institute of Radio Engineers. 7 (2): 97–126. doi:10.1109/JRPROC.1919.217425.