Building a simple compact dual rail linear bench supply - Page 1
Forum section: electronics / projects

author: jaxbird
author_rank: Frequent Contributor
timestamp: January 09, 2020, 10:14:48 am
content: Build a simple dual rail linear bench supply +/- 30V and up to 50W output based on LM317 and LM337 regulators.

author: jaxbird
author_rank: Frequent Contributor
timestamp: January 09, 2020, 10:16:34 am
content: Schematic:

author: jaxbird
author_rank: Frequent Contributor
timestamp: January 09, 2020, 10:24:18 am
content: The design is based on an old datasheet application note but updated with a few changes to make it more accessible and expanded to become full dual rail

author: rstofer
author_rank: Super Contributor
timestamp: January 09, 2020, 07:11:06 pm
content: Very professional appearance. The Polyurehane trick alone is worth the time to watch. One of my projects has the printed legends sandwiched between 2 1/8" acrylic sheets. It works well but your method is slick and probably less time consuming and much more applicable to use on small panels.Great project!

author: jaxbird
author_rank: Frequent Contributor
timestamp: January 11, 2020, 08:45:18 am
content: Quote from: rstofer on January 09, 2020, 07:11:06 pmThanks, yeah the polyurethane trick really works very well, just give it a light coat first to make sure the ink doesn't run, then follow up with 2-3 full coats, it will completely impregnate the paper and it becomes very strong.Then I glue it to the front using 3M Super 77 spray glue, really easy and quick way to make a custom and very durable front panel film.It does make the paper slightly cream color, but I really don't mind, actually it probably looks better than pure white.

author: rdl
author_rank: Super Contributor
timestamp: January 13, 2020, 03:42:50 pm
content: Try using something Like Krylon Clear. It will do basically the same thing as the polyurethane in this application, but it's acrylic based and has no color at all and will never yellow. You can get it in matte version also.https://www.krylon.com/products/crystal-clear-acrylic/

author: jaxbird
author_rank: Frequent Contributor
timestamp: January 15, 2020, 01:38:19 pm
content: Here running a few comparison test with the older Korad KA3005 linear supply and a newer Longwei LW-K3010D switchmode supply.The tests are:Peak short circuit current while current limitedOutput impedanceDynamic Load

author: jaxbird
author_rank: Frequent Contributor
timestamp: January 30, 2020, 06:57:02 pm
content: Quote from: rdl on January 13, 2020, 03:42:50 pmIt's a good suggestion and worth a try if they have a nice satin finish, In my experience urethane based paint is much stronger than acrylic and I kind of like the slight cream color tint I get with the polyurethane lacquer.

author: MarkF
author_rank: Super Contributor
timestamp: January 30, 2020, 08:47:24 pm
content: So, you clear coat the label BEFORE gluing it on?My first impulse would have been to do it the other way around.I have just used clear packing tape 3" wide over the label on my last project.I like the technique. I'm going to try it the next time I need a label.

author: moffy
author_rank: Super Contributor
timestamp: January 31, 2020, 01:49:53 am
content: there might be a problem with the design. If you lose the connection between the pot and the 'adj' pin the output of the regulator is going to go high. If a pot develops a dead spot or fails you could get the full input voltage across your test circuit which you are powering. It would be better to fail safe or low output voltage. The 'adj' pin needs, say a resistor permanently connected, to make the output voltage low in the case of a failure of the pot or connection.

author: jaxbird
author_rank: Frequent Contributor
timestamp: February 09, 2020, 04:58:45 pm
content: Quote from: MarkF on January 30, 2020, 08:47:24 pmYes, just print, coat with satin polyurethane, multiple coats until the paper is totally impregnated. Then I use 3M Super 77 spray adhesive to glue it to the surface. It gives a really nice satin finish and very durable surface.

author: misa2
author_rank: Newbie
timestamp: May 17, 2024, 11:16:32 pm
content: I have built this power supply from junk parts, and i can recommend the simplicity of design. Of course, tracking uniformity (and current limit) depends on quality of stereo pots. I have built my own PCB, that uses external smoothing capacitors, rectifier and regulators, because i had large caps and small plastic case. The kicad files are attached if anyone needs them.I had a lot of trouble with fake components. The simple one was LM334 from aliexpress - random PNP bjt with laser etched markings. The hard one was LM317 from local store here in Belgrade. It works correctly up to 200mA, and then it refuses to increase the current. The store replaced them for free with genuine parts.Thank you jaxbird, for sharing this.

author: David Hess
author_rank: Super Contributor
timestamp: May 18, 2024, 03:11:38 pm
content: I used to use Krylon acrylic to spray paper front panels but they were never tough enough. Now with spray adhesive, I place a Mylar overhead projector film sheet over the paper, which is incredibly tough and resistant to chemicals.