OT & BTW (this references a project from last fall). I never did thank you Sarge for the idea of using a LM317 in current limit mode on the motorcycle's LEDs. Brilliant solution to the fluctuating voltage. Wired it onto a mini-board with a barrier strip for the line connections. Works perfect!

No big deal, and you're welcome

The LM317 as a current regulator isn't ideal, due to the relatively large voltage drop (3v) when used in this manner. However, it's one of the most simple ways to achieve decent regulation, without wiring a bunch of components together.

 

Actually, I had planned on incorporating an op-amp to control the negative rail (schematic/plans/circuits from Laurier Gendron's site, Bill Bowden's &, of course, AAC ). I am open to ideas

I have no idea what all that refers to Doug.

Here's what I had in mind.
You will have to derive your Vref as you seee fit. And you could use an f.e.t. in place of the b.j.t.
But where do you stop? It is departing from the simplicity and attraction of the 317 and siblings. Any more than this, or perhaps just this alone, and you may as well design you own to start with!
Oh, by the way, I have found that Colvern's wire-wound potentiometers are as linear as you are likely to find, but that's not to say that there aren't other manufacturer's products which are too. And on the subject of dual-ganged pots, I found that on Bourns there is lost motion between the front and rear sections, which, in some applications, can rule them out.

 

Hi Doug ... Did you get this issue fixed?

I had a similar situation myself and fixed it by using a LOG pot wired as shown in the attachmant here.

I sometimes find myself looking too deeply for fixes!

Hope this is of interest. Tom.

 

natsys wrote:

... Did you get this issue fixed?

Yes, & thanks. Sorry for the long delay in response. I get side tracked.

In the end, I went w/ a dual gang pot (1k & 500Ω). It works satisfactorily, but does fall short of my desires. However, as noted in Bill Bridgen & Sgt Wookie, I was rapidly departing from the initial intent to keep it simple. It's the first benchtop PSU I've built & I can't complain - I have adjustable voltage & current for my breadboard projects.

I will continue to experiment with the design & will give your solution a try when I get ready to build the next version.

My thanks to all at AAC who helped me work this project.

 

Yes, & thanks. Sorry for the long delay in response. I get side tracked.

That's good Doug ... glad that you've made progress. A bench PSU was the first thing I made for myself many years back; it served me well at the time and is still working. It was based on a pair of LM723s for a dual output through a couple of 2N3055s. I hope you have success with what you're doing there ... good luck

Cheers ... Tom.