A constant current (steady current, time-independent current, stationary current) is a type of

direct current Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...

(DC) that does not change its intensity with time. The syntagma stationary current is a contradiction in terms, however in use.

Sources

If the load is constant, a steady current can be obtained via a constant voltage source. If the load is varying, a steady current can be obtained via a constant current supply source.

Constant voltage sources

electrochemical cell An electrochemical cell is a device that either generates electrical energy from chemical reactions in a so called galvanic cell, galvanic or voltaic cell, or induces chemical reactions (electrolysis) by applying external electrical energy in an ...

is a device capable of either generating

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

energy from

chemical reactions A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products ...

or facilitating chemical reactions through the introduction of electrical energy. A common example of an electrochemical cell is a standard 1.5-volt cell meant for consumer use. This type of device is known as a single

Galvanic cell A galvanic cell or voltaic cell, named after the scientists Luigi Galvani and Alessandro Volta, respectively, is an electrochemical cell in which an electric current is generated from spontaneous oxidation–reduction reactions. An example of a ...

, so an obsolete name for steady current was galvanic current. A ''battery'' consists of two or more cells, connected in either parallel or series pattern. A

homopolar generator A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and ...

is an

electrical generator In electricity generation, a generator, also called an ''electric generator'', ''electrical generator'', and ''electromagnetic generator'' is an electromechanical device that converts mechanical energy to electrical energy for use in an extern ...

comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A

magnetohydrodynamic generator A magnetohydrodynamic generator (MHD generator) is a magnetohydrodynamic converter that transforms thermal energy and kinetic energy directly into electricity. An MHD generator, like a conventional generator, relies on moving a conductor through ...

directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery. AC generators can be used as sources of steady current with a rectifier and a good ripple filter. Pulsed DC generators can be used as sources of steady current with a good ripple filter.

Constant current power supplies

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

, a constant current system is one that varies the voltage across a load to maintain a constant

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

. When a

component Component may refer to: In engineering, science, and technology Generic systems *System components, an entity with discrete structure, such as an assembly or software module, within a system considered at a particular level of analysis * Lumped e ...

is indicated to be driven by a constant current, the

driver circuit In electronics, a driver is a electrical circuit, circuit or electronic component, component used to control another circuit or component, such as a high-power transistor, liquid crystal display (LCD), stepper motors, Static random-access memor ...

is, in essence, a current regulator and must appear to the component as a

current source A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it. A current source is the dual of a voltage source. The term ''current sink'' is sometimes used for sources fed ...

of suitable reliability. An important usage of constant current

power supplies A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...

is with

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

s. While a high series resistance is sufficient to light an LED, sometimes the design needs to guard against high current (or risk burning out the LEDs). Another use is in

fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, to produce ultraviolet and make a phosphor ...

s which have very dynamic

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual paral ...

and are optimally operated within a short range of currents. Other uses include

shielded metal arc welding Shielded metal arc welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode covered with a flux to lay the we ...

and

gas tungsten arc welding Gas tungsten arc welding (GTAW, also known as tungsten inert gas welding or TIG, tungsten argon gas welding or TAG, and heliarc welding when helium is used) is an arc welding process that uses a non-consumable tungsten electrode to produce the ...

Constant Current Source Applications for LEDs

* Reliability Testing * Device Burn-in Test * HASS and IESNA LM-80 Applications * Energy Star Certification * Calibration Lamp Drive * DC Driven Lamps * Resistor Aging * Laser Diode DC Drive

References

Electric current Electrical power control Electronic circuits {{electronics-stub

Sources

Constant voltage sources

Constant current power supplies

Constant Current Source Applications for LEDs

See also

References