I think "current limiting diodes" is something of a misnomer, kind of like products marked
"unscented" which have scent in it, or like "Liberal" and "Conservative" in the political realm...
By the way, don't buy the exact 1.0 ma diode, buy one tenth ma less than or greater than (ie. 0.9 ma
or 2.1 ma). They are less than half the price of the exact 1/0 ma diodes.
Dan
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).
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