In electronics, a constant current system is a system that can vary the voltage across an electronic circuit to maintain a constant electric current. When a component is indicated to be driven by a constant current, the driver circuit is, in essence, a current regulator and must appear to the component as a current source of suitable reliability.
An important usage of constant current power supplies is with LEDs. 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 lamps which have very dynamic electrical resistance and are optimally operated within a short range of currents.  Other uses include shielded metal arc welding and gas tungsten arc welding.
- Caladen Circuit Corner, before Sep 5 2009, LED Current Controller
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