🚀 go-pugleaf

In article <1990Jul23.222401.26115@cbnewsc.att.com> jgk@cbnewsc.att.com (joseph.g.klinger) writes:
>I've been looking for JFET current limiter diodes 
>	1) they're too expensive, $5 ea for a 1N5314, down only to $0.85 
>	   in thousands for a J557 (not cheap for a quantity price).
>	2) they're hard to find, not much bigger than 10 mA,
>	   and not common
>
>How can I build the equivilent to a 10 mA AC (I want to pass both halves 
>of the AC waveform) current regulator, using cheap JFETs, resistors, 
>and perhaps zeners?
>
	Any gate-shorted-to-source junction FET acts as a current
regulator; the parts you've quoted are good for a very wide
range of bias voltages (2 V to 50 V; some go to 300V), but do you
need that?  They come pre-calibrated, or at least pre-sorted (the
assembly line doesn't permit high accuracy here); do you need that?
	If you can stand worse output impedances, consider using
an RF JFET (like J304) and sorting them yourself.
	Other possible solutions: PTC thermistors (they heat up enough
at 10 mA to raise their resistance...and choke the current off),
or ballast tubes (these are incandescent bulbs, making use
of the positive temperature coefficient of a heated wire), or even
a current-limited op amp (use it to buffer your signal).
	What frequency range are you interested in?  What impedance
(or equivalently, voltage range)?  How accurately need this limit
be maintained?  Can you tolerate distortion (a volt or so of distortion
is to be expected from a diode bridge/FET combination)?

		John Whitmore