CLD's

[plumber]

It seems descriptions vary on components enough to cause worry when ordering on line, then I walk into a radio shack, and get really confused. I need to properly describe and order a "Current limiting Diode" that will keep mA's around 6 mA. On a 30 volt dc power supply. And yes it is just a wall adaptor power supply rated to 800mA. An unregulated output shouldn't matter should it? Any help would be appreciated.
Thank you, plumber

 

[Resqueline]

Constant current diodes aren't much used any longer. I believe they tolerated 30-40V and came in the DO-35 or DO-41 case outlines. I couldn't find any such in Radio Shacks online store anyway.
But in principle they are just depletion mode FET's with two legs shorted, so you can easily make them yourself, just get the right transistor for the current wanted. There will be a small spread in the current you get, even between the same type numbers.

 

[plumber]

Thank you again Resqueline. I'm dying here. I've been trying to absorb as much knowledge as possible to utilize the solutions and suggestions on this and other forums. My brain is fried. Will you please help me with which FET I need for anything around 4 to 6mA using a 30 vdc supply? How to wire it, which legs to short out and how? I know I sound pathetic. As soon as I learn about "field effect transistors"...it all breaks down when I try to specify which one I want to buy because I am still learning the terminology,math and theory. A "current limiting diode" sounded so easy to me.
plumber.

 

[Resqueline]

There are many solutions and parts that''ll fit your bill, I'd have a hard time choosing one myself, though I always favored the bipolar transistor constant current source..
But if you Google "fet constant current source" you'll find many recipes. Wikipedia is a nice source of knowledge as always, with useful links.
The depletion-mode FET is also known as a JFET. It needs a negative gate voltage in order to turn off the current (hence the name depletion-mode).
Maybe you can still find constant current diodes somewhere but I don't know where.