IV.5 - Current Limiting diodes?

Constant current two-terminal devices can be made by shorting the gate and the source of a JFET together. When the FET is forward biased, this results in a nearly constant current for voltages ranging from roughly 2V up to 300V (or the breakdown voltage of the device in question). In reverse bias, this kind of constant current device conducts as a junction diode (so one can oppose two such devices in series to regulate AC current).

Siliconix makes two-lead FET current-limiting diodes ranging from 0.24 mA (J500) through 4.7 mA (J511) in plastic packages, and from 1.6 mA (CR160) through 4.7 mA (CR470) in metal TO-18 packages.

National Semiconductor makes a three-terminal adjustable device, the LM134/LM234/LM334, that acts as a resistor-programmed current source diode, analogous to the 'programmable Zener' TL431. Adjustment range is 1.0 uA to 10 mA, and voltage compliance is from 1V to 40V (or 30V for some versions). The current is slightly temperature-dependent (this may be useful, or can be eliminated with a diode added to the adjustment resistor).

Motorola used to make current-limiting diodes, MCL1300 series, with 75V operating range and 0.5 mA to 4 mA current. I think they've stopped offering these.

• Siliconix, 2201 Laurelwood Road,Santa Clara, 95054-1516, USA
  Phone (408) 988-8000
  Fax (408) 727-5414
  
• National Semiconductor, 2900 Semiconductor Drive
  P.O. Box 58090, Santa Clara, CA 95052-8090
  Phone: (408) 721-5000
  
• Central Semiconductor Corp, 145 Adams Ave, Hauppauge, NY 11788
  Phone (516) 435-1110
  Fax (516) 435-1824
  (Mouser stocks these diodes, like the 1N5305)