Using a LM317 as a current regulator....

[flash....]

Good Idea or Bad???
I see so many other circuts used for this and I'm no expert...
What are the major disadvantages using the LM317 to drive a 5W LS vs. other solutions?
Any searches I find for the LM317 don not exist on the new CPF board.
The LM317 is so simple to use, if there are no real downsides, why not use it?

 

[JSWrightOC]

I think the biggest problem is the relatively high dropout voltage. The device has a dropout of 2-3V, and your sense resistor will always drop 1.2-1.25V, for a grand total of 3.2-4.25V. You could run a whole 1W LS off that.

For battery charing circuits it's great, because then you really aren't concerned about losses.

 

[INRETECH]

His statement is correct, in a flashlight - you have a finite amount of energy, and you do not wish to waste a bit of it

Your most eff unit would be a switcher

 

[tonyb]

Re: Using a LM317 as a switching regulator....

The LM317 makes a nice switching regulator I have built many swicthers of well over 90% eff. with this regulator. Check Nationals website for schematics.

 

[whiskypapa3]

Re: Using a LM317 as a switching regulator....

The LM317 also makes a wide band splatter generator. A ham friend used one in a switching mode power supply and it sounded like one of my old jammers on the 80 meter CW band. Just as good as a cheap TV set.

 

[tonyb]

Re: Using a LM317 as a switching regulator....

Thats because a square wave is composed of a fundimental frequency and a infinite number of sinewaves each with its own unique amplitude and phase relationship hence all the radio noise.

 

[flash....]

Re: Using a LM317 as a switching regulator....

Thanks for the input all!!

Tonyb, I looked at the schematics for turning the LM317 into a switcher, And I can do that but I want something much simpler.

I just wish someone would make a turn-key switching Buck\boost regulator similar to whats in a KL1 that is adjustable for current.

You know, 4 leads (2 in & 2 out with an adjustment pot for current and small)
Then I would be in heaven!!
I was hopeing I'd found a super simple package with the LM317.

Thanks again...

 

[mrme]

I just modified a headlamp with an LM 317 regulator. I set it up so it would run a 6 volt bulb with either 2 set of 4 AA's in parralell direct drive or all 8 with the voltage reglulator. I figure it is 100% efficient when I keep it direct drive and super bright when I need it to be.

 

[Hemingray]

I've used LM317 and LM350 as current (as well as voltage) regulators for a long time. As previously mentioned, the LM's internal drop plus the 1.25VDC adds up to an appreciable waste of power, but if this is being used in an automotive circuit, this is of little consequence. Not the best aproach for a bundle of 8 or 9 AAs, however...

THere are switching equivalents of teh 7805 and 7812 linear regulators, perhaps there is a switcher equivalent of an LM317 or LM350?

/ed B in NH