current limiting diode

Lightfoot

I know how and when to use them, one problem. What is a name for one that is rated at three amps (such as 1N4007)?

Thanks

RickB

If you are refering to constant current diodes, those are just jfets with the source connected to the gate as 1 lead and the drain for the other. Never heard of a current limiting diode, but you might be able to make one with a power fet. Look up "constant current" and "fet" w/google

Rick

Paul Baker

Do you mean a voltage limiting diode? Zener diodes are designed to "breakdown" when a certain reverse polarity voltage is across them, this is frequently used to clamp a line to a maximum (or minimum) voltage. The Vibratab sensore Parallax sells uses this method to make it safe to connect it to a stamp.

If you are refering to a current rating, that is just a parameter and it is not self limiting, a diode rated for 3 Amps can carry more than that if you do not design the circuit properly, but you will cause it to· burn out. And if your not careful it will explode, the glass vartieties can send shards of glass flying.

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Post Edited (Paul Baker) : 12/9/2005 2:00:34 PM GMT

Lightfoot

Yes, I mean current limiting diode.· I googled them both however it does not tell me a name so I can order it.

SteveW

I don't think I've ever seen a 2-terminal current source anywhere near 3 amps. 25mA is much more like it. I suspect you'll end up having to build something yourself, probably easiest to use an LM317 in constant current mode. However, I'm slightly concerned at why you need a constant 3 amps - it's an unusual requirement, and you've not specified it very tightly - no hint of the voltage range it has to work over, the load it's expecting, or any of the other things that could trip up the unwary.

Steve

Tim-M

Lightfoot,

· A 1N5408 diode·is rated at 1000 PRV (Peak Reverse Volts) and 3 Amps of current, if that helps.

Tim

Paul Baker

I was going to chide you for not doing enough research, but I see that google doesn't place the link I found anywhere near the top. When doing research, it's best to try several search engines, because each uses different criteria for link relevance (I use google, yahoo and kartoo regularly (I don't use MSN because they are more biased in thier rating system)). When searching Yahoo "current limiting diode", the first paragraph of the 4th link·(Titled "Boosting the Current Limit of Current Limiting Diodes") says:

Sze Chin of Central Semiconductor Corp. said...
The current limiting diode (CLD) or current regulating diode (CRD), despite its simplicity and distinct advantage over a conventional transistorized current source, has limited use. One reason is that presently available CLD’s can provide current regulation only up to 15mA maximum, and in terms of power, only 1 watt maximum. Hence, the usefulness of the CLDs is limited to low power applications such as telephone line circuit modules, handheld devices and single IC chips or small areas of a PC board.

Read the remaining article to see how he uses a CLD in conjunction with a BJT to achieve higher currents. It appears you will have to do this to get your 3A current limiting. He's also kind enough to provide a part number for the CLD he used (CCLH150 a 15mA CLD).

But thanks for bringing CLDs to my attention, it solves an issue Ive been kicking arround for how to supply 15mA to an LCD backpanel (no Vf provided in specs, though a kind soul on the forums provided a Vf through experimentation, I hate using a simple resistor on an important element).

PS if you don't want to goto different search engines, use a metasearch engine. www.dogpile.com is a good standard text based search, www.kartoo.com is a graphical based metasearch engine, which I am quite enamored with, it provides a great search refinement interface.

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Post Edited (Paul Baker) : 12/9/2005 6:10:48 PM GMT

Lightfoot

thanks for the info