Anyone using Current Limiting diodes - Page 1
Forum section: electronics / projects

author: robrenz
author_rank: Super Contributor
timestamp: April 08, 2015, 04:08:47 am
content: I found out about these being used in the battery powered supplies for PCB ICP accelerometers.I got some to do my own home brew power supply for my accelerometer and they are pretty neat.Wondering why I have never heard of these before?Article about themherePCB info on signal conditioning using the current limiting diodehere

author: edavid
author_rank: Super Contributor
timestamp: April 08, 2015, 04:26:32 am
content: Well, they are covered in "The Art of Electronics" (2nd ed). They are just JFETs that are screened for tight IDSS ranges... which makes them expensive. Usually there is a cheaper and better way to accomplish the same thing.

author: Ian.M
author_rank: Super Contributor
timestamp: April 08, 2015, 04:29:54 am
content: Any time you use one with one terminal connected to a supply rail or ground, a conventional current source or sink circuit will be cheaper and probably better as well.

author: SeanB
author_rank: Super Contributor
timestamp: April 08, 2015, 04:35:58 am
content: The only redeeming feature they have is simplicity, dating back from when an IC was an expensive thing, and the opamp was a thing that needed 15V rails at a minimum. You can get better performance from a LM344 or a LM317 over a similar current range for a floating supply, or just use a opamp current source if you want tighter control.

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 08, 2015, 01:35:40 pm
content: I've used an LM317 in the past rather than a FET due to the poor Idss tolerance.I am also jittery about using a device that is not second/third sourced.

author: robrenz
author_rank: Super Contributor
timestamp: April 08, 2015, 02:17:29 pm
content: Is there something simpler than this circuit that I am using exactly as shown? One component current limit.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2015, 02:24:01 pm
content: What current do you need?

author: robrenz
author_rank: Super Contributor
timestamp: April 08, 2015, 02:48:31 pm
content: 2 mA. I am already using the current limit diode and it works perfectly. I just had never heard them mentioned.They were $2.30 each from Mouser.

author: rdl
author_rank: Super Contributor
timestamp: April 08, 2015, 11:07:42 pm
content: The cost vs. simplicity trade off is the thing. You can find constant current circuits that are more "constant" using a couple of transistors and resistors. Cost less than 50 cents, but uses more parts. For a one off project or similar, more expensive but only one part may be an advantage.

author: dannyf
author_rank: Super Contributor
timestamp: April 08, 2015, 11:36:00 pm
content: Quote=Jfet + a resistor.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 09, 2015, 12:15:13 am
content: CRDs are very botique, so you almost always want to substitute with something else, like a depletion MOS (common enough these days; presumably, the free gate terminal offers enough functionality to make them worthwhile in many applications besides current limiting), or just a current source/sink circuit (which looks perfectly acceptable in that diagram, providing bias from a fixed, and ground referenced, supply).Tim

author: dannyf
author_rank: Super Contributor
timestamp: April 09, 2015, 12:18:46 am
content: QuoteA resistor would work in that case.