1st project with help from forum! - Page 1
Forum section: electronics / beginners

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 04, 2017, 08:10:58 am
content: I started watching these videos last spring then joined the forum last fall. I went from almost no knowledge of electronic to building this:It takes a 5-35 VAC/ DC Connection and makes a fine tune adjustable 2-22VDC @ 1A, through the magic of an LM317 which is not a mosfet.I beefed up the parts above spec, added a fine tuning pot for voltage a big heat sink, and indicators that change brightness with output. One stays constant so you can reference a rough voltage your getting out.This forum was a huge help! Now I can power any small electronics with just about any linear wall power supply.

author: ebastler
author_rank: Super Contributor
timestamp: March 04, 2017, 04:45:03 pm
content: Well, congratulations on completing your first homebrew electronics project!A few suggestions for tweaking the build, or for your next project:I would recommend using heatshrink tubing for the three connections to the LM317 (isolating each one individually), instead of the hot glue you have applied. If these wires should short against each other, or against the heatsink, that could cause the full input voltage to show up at the output, killing your connected load. Better to play this safe!A similar suggestion regarding the rectifier PCB: Is its bottom well-insulated, or could it short against anything (e.g. the input jacks) if it moves around? Also, I can't see a big capacitor behind the full-wave rectifier. Is there one hidden underneath? The one on the vertical board seems a bit small. The LM317 will do its best to keep the output voltage stable even if its input has AC fluctuations, but the rectifier and capacitor need to at least make sure that the unregulated voltage never drops below the minimum needed to provide the desired output voltage. Do you have access to a scope to check the ripple (AC component) on the voltages?When using the power supply with a high input voltage, low output voltage and significant current, you probably have to keep an eye on the internal temperature. At 30V input, 5V output, 1A current, the heat sink would have to dissipate 25W. The heat sink seems to be fully enclosed in the case? In that configuration, it would probably get quite hot quicky, since the heat can't go anywhere. Bench power supplies often have the ribs of the heatsinks arranged out in the open, on the back of the enclosure; or they use vents in the enclosure and often a fan for forced air flow.Finally: One thing you have probably learned from this project is that mounting and wiring up the various independent components -- multiple PCBs, input and output jacks, potentiometer, regulator and heat sink -- tends to take a lot of time, can be a hassle, and is error-prone. As you gain more experience with the circuits you design, it pays off to plan ahead a bit further: Think about the arrangement of components in the enclosure, arrange them all on a single PCB (where it makes sense -- there are many well-justified exceptions to that recommendation), think about how to attach your PCBs to the enclosure etc..But that's for your next project! Have fun with your LM317 supply, and with whatever you build next!

author: Electro707
author_rank: Contributor
timestamp: March 04, 2017, 09:09:58 pm
content: When you said:QuoteRemember that the input voltage must be higher than the output voltage by ~3v as stated in the datasheet.Regarding temperature the IC(The LM317 is considered an Integrated Circuit) has a over temperature and current protection built in so the chip should save itself in case you try to pull too much or it overheats.I recommend that you keep the input-to-output differential voltage between 4-7V as the chip heats up quicker as the difference is higher.Nice project for a beginner as you had no previous experience. The only you'll get better is by trying and experimenting.Anyways good luck with future projects, and remember we're always welcome to help you.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 08, 2017, 04:25:42 am
content: You cant see it but there is a huge cap (1"X 3/4")just under the bread board, thats at a higher (almost double) uf value in the schematic with the exception of the lm317 every connection is heat shrunk and the bottoms of the boards and after I took that pic everything else is coated and secured into place with silicone, LOTS of silicone, almost like its potted and could probably survive a quick dunk under water. I accidentally shorted the leads of the cap right before I started sealing everything in silicone and the leads started smoking the insulation of a near by wire touching them but the LM317 and everything else was ambient temperature. I got kind of impatient with the last step which was putting the lm317 into place, hence the hot glue. I don't plan on using it run anything near 1 amp load, it mainly just runs really simple led circuits and is for testing things. Everything I tested doesn't even make it warm. The only part the gets warm (maybe 10'C hotter) is the resistor that powers the power on indicator LED. The heat sink is really just there to buy time when I accidentally short something, as happened once when I dead shorted it for about five minutes until that whole heat sink was well over 100'C and started melting wires touching it. Without it the lm317 would have been cooked. That thing it pretty robust.

author: JRosario
author_rank: Contributor
timestamp: March 16, 2017, 11:28:59 pm
content: Quote from: raspberrypi on March 04, 2017, 08:10:58 amGreat to see other people having some success. Very encouraging!Each project I start, I go in with a lot of optimism, but the plan often falls apart into frustration.I just got back on the forums looking for some encouragement, and I thank you for that.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 11:50:29 pm
content: Quote from: JRosario on March 16, 2017, 11:28:59 pmWhere are you getting stuck?When I was a kid I had a lot of frustration trying to build things because although Radio Shack had a lot of parts still, they never seemed to have everything needed to build much of anything. These days with Digikey, Mouser, ebay, etc this is rarely a problem anymore.