Circuit achieves constant current over wide range of terminal voltages

摘要

Analog-circuit design often re-quires a constant-current sink. An example would be for a TRIAC (tri-ode-for-alternating current) dimmerrnholding current in fluorescent or solid-state lighting. Other examples include a precise current sink at the end of a long line, such as a cable or an ADSL (asymmetric digital-subscriber-line) modem, which produces a "signature" current value that alerts the device at the source end, such as an exchange office or a cable center, that the remote equipment is attached. The trick is to make a circuit that gives a constant current over a variety of terminal voltages.