Can you help me with a design of a smps - Page 1
Forum section: electronics / projects

author: K-Experiment
author_rank: Contributor
timestamp: March 01, 2019, 10:11:07 am
content: input: 220vac 60hzoutput: 12vdc 5aefficiency:80-100%wattage: 60w

author: Zero999
author_rank: Super Contributor
timestamp: March 01, 2019, 10:33:50 am
content: The standard advice here is to just buy one. 12V at 5A is a fairly standard requirement so a ready made one will be much cheaper than designing one, even in large volumes.Examples:https://ph.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/1618285/https://ph.rs-online.com/web/p/desktop-power-supply/0188769/

author: K-Experiment
author_rank: Contributor
timestamp: March 01, 2019, 10:38:16 am
content: thanks for your answer but where i am right now thats too expensive so thats why i am asking for help in designing an smps(i have searched but its all too expensive)

author: coromonadalix
author_rank: Super Contributor
timestamp: March 01, 2019, 10:39:02 am
content: yeah dont loose time and cash, buy one already madeA 60 watts smps wont cost a fortune, please avoid cheap china made ones. And for the price sometimes they have 85 - 240 vac inputs

author: coromonadalix
author_rank: Super Contributor
timestamp: March 01, 2019, 10:41:22 am
content: to build one, you have google as your friend, you have many things to consider before building one, ovp ocp thermal protection, pfc etc etc ...Simply take a linear transformer instead, with basic parts way simpler unless space is a problemOr maybe salvage an power supply ?? 5 or 12v is pretty standard nowadays

author: Ice-Tea
author_rank: Super Contributor
timestamp: March 01, 2019, 10:55:44 am
content: You'll never beat a ready-made PSU on price by cobling something together out of parts. A decent PSU will cost you, what, 20$?Or else you can dig up an old ATX PSU and use that...

author: nick_d
author_rank: Regular Contributor
timestamp: March 01, 2019, 10:59:05 am
content: Building your own SMPS will be much more expensive than buying one. I know, I have a reel of expensive double insulated mains wire (probably $80 plus $20 delivery from the UK) and a big box of coil formers and such from Digikey (expect to pay $10 to $20 per transformer plus the delivery etc), have tried several SMPS chips with and without internal FET (another $10 to $20 per chip as you'll need to get at least 10, you will blow up about 5 of them), the FETs, the voltage references, the opto isolators... etc etc. Why did I do this? Because I was willing to spend thousands in cash and time to learn about SMPSs. If you are too, then do it!A cheaper route is to pull apart broken SMPSs and put together a Frankenstein with the controller from this, the transformer from that, etc. But, this requires MUCH more skill and frankly if you have that skill you should be working at a high salary not making one off PSUs. Also the transformers and other parts are quite fragile and usually get damaged during the disassembly.Nick

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 01, 2019, 03:16:10 pm
content: This is just not any SMPS, it's necessarily an isolated one powered from mains. Safety is a real concern, so designing this if you've never done that before is a hazard IMO.Also, this usually calls for a flyback topology, and it's full of potential traps if again you're new to this.As for the cost, unless you can find ready-made parts (especially the flyback transformer) that exactly fits your design, you'd have to design the transformer and have it custom-made or try finding an off-the-shelf one (while exactly understanding what you're looking for). Forget about it.As said above, buying an off-the-shelf supply will be cheaper even from your country. Unless maybe you're going to have tens of thousands of them manufactured. And even so, with those quantities you'd be able to get pretty nice deals with many chinese suppliers, so...

author: Siwastaja
author_rank: Super Contributor
timestamp: March 01, 2019, 05:35:46 pm
content: With your specs and assumed experience (if you knewanythingabout it, you wouldn't ask like this), assume about 1000 hours build time (about 2 years of calendar time, if you start now, assuming some basic knowledge) + about $2000 in tools and parts.You'll learn a lot, and I recommend taking massive, difficult projects for learning purposes, but if you just want the power supply, this isn't the way.

author: Bassman59
author_rank: Super Contributor
timestamp: March 01, 2019, 06:03:29 pm
content: Quote from: K-Experiment on March 01, 2019, 10:11:07 amThis runs off of your AC mains. If this is your first such design, follow the advice of others and just don't even try. Buy something off the shelf so you don't kill yourself.

author: BravoV
author_rank: Super Contributor
timestamp: March 01, 2019, 06:06:56 pm
content: Quote from: K-Experiment on March 01, 2019, 10:38:16 am1st the most important thing, what is your max budget for components ? $1? $10? $20? and so on ...As this will help experienced people to give you a clue if its possible or not ?

author: chris_leyson
author_rank: Super Contributor
timestamp: March 01, 2019, 06:55:15 pm
content: You can't build them cheaper than you can buy them and as it's an offline supply then you need to consider safety, things like creepage and clearance distances across isolation barriers especially in the transformer design. If you are thinking about building thousands of power supplies instead of a one off then you can build them cheaper.

author: Zero999
author_rank: Super Contributor
timestamp: March 01, 2019, 08:10:32 pm
content: Quote from: K-Experiment on March 01, 2019, 10:38:16 amThen the likes of ebay and Amazon are your friends: look for a second hand one. Indeed, it may even make sense to buy a broken one and repair it!The only real reason for designing a mains powered SMPS is for educational purposes, but as many people have said: it'll be much more expensive than simply buying one. This is because buying components in small quantities is extremely expensive and the power supply manufacturers can purchase them in huge volumes for a fraction of the price.

author: stmdude
author_rank: Frequent Contributor
timestamp: March 01, 2019, 08:23:46 pm
content: Meanwell RS-75-12 would give you 6A @ 12V. You can find them on eBay for $22.Meanwell is a very reputable PSU manufacturer, and will give you much better performance than anything you can build for $22.

author: james_s
author_rank: Super Contributor
timestamp: March 01, 2019, 09:14:46 pm
content: Quote from: blueskull on March 01, 2019, 08:16:14 pmI think you know the sort of "cheap china made ones" he's talking about, obviously some very high quality stuff is made in China but if a power supply costs $5 retail brand new, it's probably a piece of crap.My advice here would be look for something surplus, there are tons of good used and new surplus power supplies out there available at a fraction of their original cost. I have a 12V 6A power brick style that I got for 99c at a junk store.