Looking for a power input board (transformer, rectifier, protection) - Page 1
Forum section: electronics / general

author: TacticalCode
author_rank: Contributor
timestamp: August 04, 2014, 05:14:04 pm
content: Hey everyone,I'm looking for a power input board for a power supply project I plan to do.I don't want to deal with the high voltage, re-invent the wheel and waste time not using (hopefully) already existing resources.Ideally, I need 240/120VAC input, 32VDC-ish output, and of course input protection (which I know little about).And of course a complete board as a module would be the very best case, but I'll take whatever resources are out there. Integrated (non-modular) designs, schematics, just something I can base my work on and be confident it does what it should do (work and use best-practice standards for filtering, protection, efficiency etc).(FYI: I plan on using this hardware for a power supply, a DC-DC buck converter will be used as a tracking pre-regulator and a linear reg will do the adjustable output regulation. Just like Dave's uSupply. This project is really just for me to learn new things, but I'll release the sources. Open Hardware rocks.)Any Ideas/Hints?

author: WarSim
author_rank: Frequent Contributor
timestamp: August 04, 2014, 05:21:19 pm
content: If you want a hands off power input, consider a wall wort. Built in supply is only needed if more that 5 supplies or over 10A is required. This is just because the feed cable gets too unwieldy.

author: TacticalCode
author_rank: Contributor
timestamp: August 04, 2014, 05:43:25 pm
content: My plan was to get power from old laptop power supplys, computer PSUs and alike. They are great to make it flexible and portable, but the more I think about it the more I want the option to get power from AC.

author: rob77
author_rank: Super Contributor
timestamp: August 04, 2014, 05:55:47 pm
content: what power level are you thinking about ? you mentioned only 32V DC-ish

author: TacticalCode
author_rank: Contributor
timestamp: August 04, 2014, 06:38:03 pm
content: Sorry, forgot to mention that... Everything 30W+ should be suitable. Lower-power supply can easily be done by said wallplugs. The more power the better, but really any designs/schematics are helpful for me as a reference.

author: rob77
author_rank: Super Contributor
timestamp: August 04, 2014, 07:04:16 pm
content: then i would recommend meanwell power brickshttp://distributor.meanwell.eu/webnet_eu/search/seriessearch.htmlfor your project either the RS-35 or RS-50 , the RS-35 (35W single output) series is sold for approx 14Euro over here, the Rs-50 (50W single output) is approx 16Euro.to make the mains wiring easy - use a combined europlug with switch and a fuse (and probably even with a filter).but ask a person with appropriate qualification to do the mains wiring - ar at least let such a person inspect the wiring before you plug it in.i'm using those meanwell power bricks because i don't want to design anything operated from mainsand last but not least - the price of those bricks is good enough and are available in my area.the power brick:http://www.gme.sk/img/cache/800x600/332/314/spinany-zdroj-mean-well-rs-35-24-obrazek-1.jpgand the combined euro connector:http://www.gme.sk/img/cache/800x600/806/248/napajeci-euro-konektor-schurter-gsw6765-obrazek-1.jpgbut probably you could also look after some PCB mount mains transformers - those are available in the 30VA range as well.

author: TacticalCode
author_rank: Contributor
timestamp: August 04, 2014, 09:11:06 pm
content: Those "bricks" look interesting. They come in various power ratings and are nearly perfect drop-in solutions. But they have some downsides for me:Not open hardware: I don't really like mixing open and closed... plus I don't have nearly as good documentation that I can learn from. Isn't guaranteed with OHW but often the case.No crimp connectors: I like crimped connectors. Insulated with some heatshrink. But all power supplys I found so far have these ugly screw terminals. Not a big fan of those...Form factor? Can't control that, everything else has to be laid out around that brick.Efficiency? I don't know typical figures for SMPS' efficiency, but I keep in mind there is still a buck converter with losses so I don't burn away huge amounts of energy in the linear regulator. I don't even think I need a regulated output from the AC input module - Filtered DC should be sufficient.So yes, I could use one of these complete drop-in solutions, but I'd rather be able to chose something more open and more customizable.

author: mariush
author_rank: Super Contributor
timestamp: August 04, 2014, 10:50:19 pm
content: My advice would be to stay under 30v... better go with 24v. Some linear regulators, some switching regulator chips are only rated for up to 32v so I hope you can see why 32v-ish would be bad. This power supply would be more compatible with 24v output.If it's a home project, a one-off power supply, then just go and get a classic transformer, either regular or toroidal, doesn't matter. Add a bridge rectifier and some capacitors and you have your 30-50v DC output.A 24v AC transformer will output about 32v peak DC after rectification, and depending how much capacitance you put after you can get very close to 32v.Alternatively, get a 30v AC transformer which will give you about 40v peak DC after rectification so even with about 3300-4700 uF capacitance, you'll have 34-40v DC. A simple linear regulator like LM317 can make that a steady 32v DC.For 30w output you're looking at a 50VA transformer .. here's a good example:http://uk.farnell.com/pro-power/ctfc50-15/transformer-50va-2x-15v/dp/1780858Put primaries in series for 230v, in parallel for 115v ... put secondaries in series for 30v AC rms.

author: TacticalCode
author_rank: Contributor
timestamp: August 05, 2014, 03:10:51 pm
content: Sorry, I think we miss the topic here...Yes I could whack in a complete power supply or a transformer+rectifier+caps. But I'm still looking for open schematics/layouts/designs as reference. WITH (here comes the important part): protection.Beyond "let's just hope it doesn't catch fire". Also input filters seem to be a thing.I don't know about these things, so I need a design that does them right so I can learn from that.

author: rob77
author_rank: Super Contributor
timestamp: August 05, 2014, 05:12:40 pm
content: what open design you want for transformer+rectifier+caps ? sorry i don't get your point.

author: TacticalCode
author_rank: Contributor
timestamp: August 05, 2014, 07:12:47 pm
content: I'm looking for any projects that feature a proper mains power input, including protection circuitry and filtering.Normal step-down transformer or switching doesn't matter. Really, everything BUT the transformer+rectifier+caps matter. Yes I know it's a one-off hobby project, but I still want confidence that it's safe (e.g. surge protection).

author: WarSim
author_rank: Frequent Contributor
timestamp: August 05, 2014, 10:13:19 pm
content: Beyond basic XFMR Bridge Caps this is controlled by local regulations.Some places require fuse links above various power. The type and requirement of superstores vary with location. Input filter requirements are entirely dependant on use and load dynamics.There is no everything for everyone schematic.