First project on EEVBlog, long time patron.. Power Supply Planning - Page 1
Forum section: electronics / beginners

author: itsme_Bernie
author_rank: Newbie
timestamp: February 03, 2023, 11:41:08 pm
content: Hi EEVBloggersIf I need to break this post up into different forums, please let me know. Since I am so new to actually posting on this forum, and somewhat new to electronics, maybe someone can guide me a bit?* Update *I should start by saying that I have NO idea where to begin regarding planning the benchtop power supplies I want to build. I know what parts I have to work with, and a few ideas what I want to power. I was hoping I could find some threads here or youtube videos to give some basics about certain elements of power supplies that are most commonly used together, or NEVER used together, for instance.If there are YouTube videos or posts I should read before posting the topics below, or planning out a system of power supplies, portable, bench, small, big.... please let me know as I have been googling and reading EEV posts for a while now and can’t seem to find some info I think I need to move forward. I have watched many of Dave’s videos, but maybe I missed one that might help?I have a few things I am working on that are sort of related:-I am working on several bench power supply builds, and have been reading like crazy to learn how to PLAN them and design them sensibly and for efficient use.-I believe I have many useful components to get myself started-I have a great DIY Bench Power Supply I acquired (in another post for reasons revealed there) which may need a little attention, but a great start.-I would appreciate some help deciding whether to fix that or part the DIY Power Supply out to make other bench supplies with it’s components? It is a linear supply, and is based on a multitap, wound transformer I cannot identify.-Do I make my other power supplies totally digital/switching?-I can utilize some Variacs (if that is a good idea) that I have in these new power supplies if they should be used. They are panel mount, not the free-standing ones. Any reason to not use these in conjunction with those digital Buck or Boost converters we all see (like DROK, or on Ebay or Amazon) if they are AC friendly?.-I have components to put together a switched power supply with a few options of ATX and several of those ATX breakout boards.-I don’t know if those digital buck/boost converters work better with linear or switched power supplies, but I would like to set up so I can get the 40 to 60 volts that some of my step-down converters are capable of on their INPUT sides.I would also like to arrange several small portable buck and boost setups, and include some of these in the above power supplies to make them more versatile.-I have several nice Bourns 3450 10 turn Potentiometers I can swap into places in any of the power supplies I make.-I have been keeping lots of housings for other electronic devices etc, so I have housings for my projects.Thank you for any help or direction you folks can offer me!Bernard

author: donlisms
author_rank: Frequent Contributor
timestamp: February 04, 2023, 08:22:58 am
content: I read your post a couple of times, and I gotta say... I'm still not entirely sure what you want accomplish! I mean, in general, yes - power supplies. But specifically, I can't ferret out your goals, so "how to get there" can't really be answered.So I think the first thing would be to share what you see as your big picture - just learn? Make things? Fix things? What makes you think you need a power supply anyway?In general, I think the path should be something like:defining what you want to accomplish (in specific detail), which no one else can do for you, though perhaps might advise,designing the thing (including learning all that is necessary) such that you have a complete picture of what the the thing is supposed to be when it's finished,prototyping the thing, which requires the parts you decided on in your design, and making the thing work,fixing the issues,perhaps finishing it up nicely, or perhaps going back and deciding what you want to accomplish and starting over!I don't think you have to be strict in these things, but when you say "plan", I think getting some structure like this will help. So more specifically: (1) decide what you want to build. Please say "a single, simple, linear supply." Not because you're dumb, but because project complexity is always at least 10 and maybe 100 times more than you thought it was going to be. Decide on the voltage and current. These might conveniently turn out to be values that work well with parts you already have. (2) design. Schematic. Every component pinned down. (3) decide how you're going to build the prototype. You'll need all the parts, pinned down. Interconnections pinned down. Basic packaging. You know you're ready when you could give a set of instructions to a qualified stranger, and expect success. (4) the rest of it, like that.There's probably a lot that could be added to all this; I'm just kinda hoping it gives you some structure in which you can do your planning.

author: tautech
author_rank: Super Contributor
timestamp: February 04, 2023, 10:19:15 am
content: A DIY PSU is an integral part of initiation into this hobby....we've all been there.Recommend initially you KISS with a basic linear design and just a LM317 and rely on its internal current limiting or if you really need some grunt and have the transformer to supply it use a LM338 instead.Study their datasheets typical applications.Don't be mean and be sure to use a 10T pot for any adjustment capability.Later you can rebuild the internals of whatever enclose you put it into to add to its complexity for it to better suit your needs as they develop.After having trodden this road you will better appreciate the commercial products available and the features they offer as not so outta budget as you once imagined.

author: itsme_Bernie
author_rank: Newbie
timestamp: February 05, 2023, 10:09:36 pm
content: Thank you so much DonYour observations and advice is very helpful. I looks like I should have started my post saying "I have no idea where to begin." (I have updated my post so it is more clear)I thought there might at least be basics that most experimenters or repair technicians would say like "most people will run into this very often," or certain components that are commonly paired together, or even components that are rarely (or a bad idea) to house together, and so on.Hah I will be trying to keep these first supplies pretty simple and linear. I do have more than one to do though, but I definitely need to finish one before starting any others.I already know I would like to be able to feed some higher power (200w to 400w) adjustable DC to DC buck converters and boost converters. It looks like it would be helpful to have access to 30 to 40 DC volts, up to three to four amps to utilize the converters I have. I have a home machine shop and other projects that require different degrees of power. I will need to accommodate low amp and higher amp outputs, and only use the higher amperage outputs when necessary.I have quite a few options for enclosures, but I have started with some larger desktop hard drive enclosures with aluminum housings, as opposed to plastic or stamped steel. They look nice, have some room to work inside, and are thick enough to mount to. I will attach some pics.I will make sure I search more thoroughly through the archives here to see how people power these things. I guess I should also make sure I have exhausted the search “Variac power supply” and see if I missed anything.Thank you so much for your time and framework for me to plan. It may seem very basic to you, but even knowing that this is what people do is very helpful to me.Bernie

author: itsme_Bernie
author_rank: Newbie
timestamp: February 05, 2023, 10:28:57 pm
content: Thank you TauTechI will definitely be keeping them as simple as I can for now. I may well end up buying commercial power supplies someday.I will look up the LM317 and LM338, and see what will work. I have several "obsolete" (according to Bourns) 10-turn 3450H-HYB-202 2K OHM 10-TURN 5Watt Potentiometers. I have to look up how to hook them up without burning them out since they are only 5 watts.Bernie

author: tautech
author_rank: Super Contributor
timestamp: February 05, 2023, 10:39:25 pm
content: It's not rocket science if you KISS Bernie.My first proper one used 2 old 12V lighting transformers and configured with a switch for series or parallel mode depending on needs, voltage or current.Then through a bridge we calculate VAC * 1.414 and smoothed for nearly 34V less headroom losses in the regulation stage.The advantage of a switch transformer approach is the same as tapped secondary by reducing the regulation input voltage and therefore thermal emissions from the regulator and the need for large heatsinks.Buck/boost is another way around needing large heatsinks but with additional design complexity.Quote from: itsme_Bernie on February 05, 2023, 10:28:57 pmYou will after studying datasheet realise you don't need wattage for a PSU 10T pot and you might make a 2K pot work. Hunt out the online LM317 value calculators or just follow a typical app in one of the datasheets and a hint, download a few.

author: EEVblog
author_rank: Unknown
timestamp: February 05, 2023, 10:50:26 pm
content: Quote from: tautech on February 04, 2023, 10:19:15 amYep, this.An LM317 with 10 turn pot makes a nice supply.There are plenty of old Electronics Australia, ETI, Silicon Chip and other hobby magazine PSU projects out there that have articles that explain everything in great detail.

author: EEVblog
author_rank: Unknown
timestamp: February 05, 2023, 10:52:02 pm
content: Quote from: itsme_Bernie on February 05, 2023, 10:28:57 pmThere is almost no current flowing through a POT in an LM317, it's just the small bias current. So it's not possible to burn it out.

author: itsme_Bernie
author_rank: Newbie
timestamp: February 06, 2023, 12:23:08 am
content: Downloaded data sheets and reading reading reading!