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

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell 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 ...

(DC) that does not change its intensity with time.

Sources

If the

load Load or LOAD may refer to: Aeronautics and transportation *Load factor (aeronautics), the ratio of the lift of an aircraft to its weight *Passenger load factor, the ratio of revenue passenger miles to available seat miles of a particular transpo ...

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

An electrochemical cell is a device capable of either generating electrical energy from

chemical reactions A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...

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, 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 th ...

is an

electrical generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, gas ...

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 a m ...

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 The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

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

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

. When a

component Circuit Component may refer to: •Are devices that perform functions when they are connected in a circuit. In engineering, science, and technology Generic systems *System components, an entity with discrete structure, such as an assemb ...

is indicated to be driven by a constant current, the

driver circuit In electronics, a driver is a circuit or component used to control another circuit or component, such as a high-power transistor, liquid crystal display (LCD), stepper motors, SRAM memory, and numerous others. They are usually used to regula ...

is, in essence, a

current regulator 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 ...

and must appear to the component as a current source 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 res ...

is with

LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...

s. While a high

series resistance Two-terminal components and electrical networks can be connected in series or parallel. The resulting electrical network will have two terminals, and itself can participate in a series or parallel topology. Whether a two-terminal "object" is an ...

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, which produces short-wave ultraviolet lig ...

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 parallels ...

and are optimally operated within a short range of currents. Other uses include shielded metal arc welding and gas tungsten arc welding.

Constant Current Source Applications for LEDs

Reliability Testing Reliability engineering is a sub-discipline of systems engineering that emphasizes the ability of equipment to function without failure. Reliability describes the ability of a system or component to function under stated conditions for a specifi ...

* Device Burn-in Test * HASS and IESNA LM-80 Applications *

Energy Star Certification In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat an ...

* 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