Constant current diode (also called CLD, current limiting diode, constant-current diode, diode-connected transistor or CRD,current-regulating diode) consists of a JFET with the gate shorted to the source, and it functions like a two-terminal current limiter or current source (analog to voltage limiting Zener diode). They allow a current through them to rise to a certain value, and then level off at a specific value. Unlike Zener diodes, these diodes instead of keeping the voltage constant, keeps the current constant. These devices keeps the current flowing through them unchanged when the voltage changes.