2-terminal current limiter "diode" - Page 1
Forum section: electronics / projects

author: cybermaus
author_rank: Frequent Contributor
timestamp: January 13, 2024, 08:13:05 pm
content: Do there exists single package 2-terminal current limiters?Sort of like how a zener diode always resists a certain voltage, but then one that always leaks a certain current.(ideally in the 20mA range)I found theLTO3092, which for some reason is called a "2-Terminal Programmable Current Source" even though it clearly has 3 terminals.And that would work, but I do not need precision, and also I would like no additional resistors needed.One of the reasons I am asking is, I have a device that seems to have them. It looks like a diode, but the required function is clearly that it needs to limit currentAnd of course no schematic and I could not find any specs.So rather then setting up some diode/resistor/transistor set, like I see examples plenty, a single package would be niceI attach the device I have ref. Mind however, I am not perse in need to know what exact devices they are, or in need to rebuild that one.Merely looking for a component that can simply limit current to ~20mA or ~10mA, and I am quite sure these components do that.(I measured them)The left one limits to 20mA and seems to be labeled B47jAThe right two limit to 10mA each, and seems to be labeled AJ.... something. Is that a letter or a logo?

author: trobbins
author_rank: Frequent Contributor
timestamp: January 13, 2024, 08:16:54 pm
content: Leaded examples:https://my.centralsemi.com/datasheets/1N5283-5314.PDFParallel to suit current; series to suit voltage.

author: TimFox
author_rank: Super Contributor
timestamp: January 13, 2024, 08:43:04 pm
content: Simple two-terminal current limiters are often JFETs with gate connected to source.Above a reasonable voltage, they keep the current at approximately Idss.

author: Nukedpanda
author_rank: Newbie
timestamp: January 13, 2024, 09:25:08 pm
content: The parts on the right marked AJ are likely thesehttps://www.onsemi.com/pdf/datasheet/nsi50010y-d.pdf. Petty convenient little parts in a small package. You can find a handful more of them herehttps://www.digikey.com/en/products/filter/integrated-circuits-ics/734.

author: Benta
author_rank: Super Contributor
timestamp: January 13, 2024, 09:35:39 pm
content: Yep, JFETs.The most common earlier was the J500 series from Vishay/Siliconix. 2-pin TO-92 and obsolete today.They're superior to IC solutions, as they start regulating the current already below 1 V.Not very precise, though. IIRC, +/- 10%.For the current ranges you need, BF245B and BF245C (TO-92) or BF 545B and BF545C (SOT-23) could do the job, but you'll have to select them, current spread is >2.

author: cybermaus
author_rank: Frequent Contributor
timestamp: January 13, 2024, 10:07:12 pm
content: Thanks@Nukedpanda. These are indeed exactly the ones.Very impressive for someone with only one post, meaning only the one above.@Benta: Indeed, building them myself with only a jfet and a resistor seems doable. But the ones you link to are mosfets?For reference, I also found these:https://www.semitec-global.com/uploads/2022/01/P22-23-CRD.pdfAnd this real IC, also hiding in a diode package, but not JFET based and very stable for proper high LED currents, but not at all able to deal with even medium frequencies:https://www.diodes.com/assets/product-showcases/AL5809Q-NPA-0316.pdf

author: Benta
author_rank: Super Contributor
timestamp: January 13, 2024, 10:18:36 pm
content: BF245 and BF545 are 100% JFETs. Dunno why you think they're MOSFETs.And no, you don't need a resistor. Just short the gate to the source.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 13, 2024, 10:30:31 pm
content: Yes. Current-limiting diodes or constant-current diodes:https://en.wikipedia.org/wiki/Constant-current_diodeI have used this series of such diodes to limit the charging current of large caps:https://www.diodes.com/part/view/AL5809/

author: Benta
author_rank: Super Contributor
timestamp: January 13, 2024, 10:48:11 pm
content: The AL5809 is an IC, not a JFET. That also explains why it stops working below 2.5 V.

author: David Hess
author_rank: Super Contributor
timestamp: January 13, 2024, 11:18:35 pm
content: Current regulator diodes are even readily available:https://www.mouser.com/c/semiconductors/discrete-semiconductors/diodes-rectifiers/current-regulator-diodes/?q=current%20diode&instock=y