Small generic solution for 3.3 or 5V from mains @500mA - Page 1
Forum section: electronics / projects

author: con-f-use
author_rank: Unknown
timestamp: April 13, 2014, 01:51:21 pm
content: In half of my projects I need to power a micro and some electronics from mains. Most of the time I simply use old cell phone chargers I have lying around. Now I was asked to build 30-50 units and I want a better solution. Something I can buy in bulk and solve the problem for all my future projects.So what's a save, cheap, small and efficient solution to get 3.3V/5V from mains at 500 mA?

author: Gazeddy
author_rank: Newbie
timestamp: April 13, 2014, 01:54:45 pm
content: limited experience in this area but id probably use a small wall wart with a transformer taking mains down to around say 8 volts then regulate from there

author: con-f-use
author_rank: Unknown
timestamp: April 13, 2014, 02:34:58 pm
content: Thanks for the reply. Cell phones chargers are basically walwarts that put out regulated 5V so that solution would be worse. What I'm looking for is a component I could build a board around or a finished board, that I can buy in bulk and be done with it. The smaller, the better.

author: nowlan
author_rank: Frequent Contributor
timestamp: April 13, 2014, 02:37:35 pm
content: pcb switcher by recom or meanwell.power international have some interesting buck converters.http://www.powerint.com/en/applications/small-appliancesI think the 500ma is forcing a transformer.Some others suggested LNK302/4 family, but only 120ma.

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2014, 02:48:33 pm
content: http://www.digikey.com/product-detail/en/RAC02-05SC/945-1401-5-ND/2652154for example.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: April 13, 2014, 02:58:28 pm
content: What about not providing an adaptor and just expect USB power from the user like this:https://www.sparkfun.com/products/8376

author: T0mn0mn0m
author_rank: Newbie
timestamp: April 13, 2014, 03:02:20 pm
content: Your best router is probably a 5v USB wall charger. But beware, avoid the cheap ones as they very rarely actually put out 5v, and have a habit of exploding. If you needed 3.3v I will still go with a wall adapter, and an LM series 3.3v linear regulator should be fine for 200ma.

author: con-f-use
author_rank: Unknown
timestamp: April 13, 2014, 03:15:02 pm
content: Tanks for your replies! Keep them coming.TheRAC02-05SCwould be perfect at halve the price.LNK306is also an option but I'd have to design a board around it and it's not isolated so quiet unsafe.

author: zapta
author_rank: Super Contributor
timestamp: April 13, 2014, 03:22:23 pm
content: Do you need to comply with any safety standard?Having an external wart/charger will make your life easier and these days that come as small as a standard mains plug.

author: con-f-use
author_rank: Unknown
timestamp: April 13, 2014, 03:26:11 pm
content: Technically I do not, but I don't want to burn peoples houses down with a projects I build. I'm open to every solution that will get the job done. As I said my main criteria are: safe, cheap, small (in that order). In quantities of maybe 50 to 100. TheRAC02-05SCwas the best so far.

author: Kjelt
author_rank: Super Contributor
timestamp: April 13, 2014, 03:28:48 pm
content: Have no complete answer for you but maybe some directions to have a look at, I see mass produced products that use the Viper Ic's from ST and also I saw some using the TEA1521T from NXP but probably now is EOL and has some successor. Both can handle rectified mains as input AFAIK.

author: LukeW
author_rank: Frequent Contributor
timestamp: April 13, 2014, 03:36:26 pm
content: CUI PBK-3-5http://www.cui.com/product/resource/pbk-3.pdfCUI VOF-6-5http://www.cui.com/product/resource/vof-6.pdfThe PBK series requires you to add a couple of capacitors and other components externally, the VOF series is a little more bulky and a little more expensive, but gives you everything you need on board, ready to easily drop in onto your existing board. These are completely isolated flyback modules, with good PCB layouts with sensible creepage distances etc.CUI stuff is pretty reputable, the modules are pre-approved with UL, TUV etc, so not likely to burn your house down or shock you like a 99 cent Wun Hung Lo fake iPhone charger.Designing your own circuit from scratch - well, you've already said that you don't want non-isolated buck ICs like the LNK30x. If you want to design your own isolated flyback from scratch one of the hurdles you'll have to deal with is design and manufacturability of the transformers - if you need hundreds of units, you'll need to design and specify the windings and structure and core choice of the transformer to suit your voltages and the controller silicon you're using, and then find a transformer factory that can make them. They're not really something you can easily just buy off the shelf that will suit your input and load parameters and your driving circuit.

author: con-f-use
author_rank: Unknown
timestamp: April 13, 2014, 05:01:13 pm
content: Very nice, thaks again.