Cheap low power isolated AC/DC converter - Page 1
Forum section: electronics / projects

author: Unixon
author_rank: Frequent Contributor
timestamp: October 30, 2017, 01:42:07 pm
content: Can anyone suggest a solution that meets following parameters:Input: 230Vac 50HzOutput: 5Vdc 50~100mAPrice: about $1 and lessBest known AC/DC bricks are 500mA+ and over $2 but these are much more powerful than required.Many of converter parts could be reduced in size and cost, but isolation is the real problem.Are there any tiny tiny switch mode transformers?Dual winding coils in one package that could make a decent transformer? However, primary to secondary isolation would be questionable here.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: October 30, 2017, 02:03:56 pm
content: Are you trying to purchase something or build your self?

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 30, 2017, 02:20:26 pm
content: Buy a bunch of dollar store PSUs and take them apart to check the build quality?

author: Unixon
author_rank: Frequent Contributor
timestamp: October 30, 2017, 03:11:00 pm
content: Finally this converter should go in mass production as a part of a larger device, hence it must be reliable and built with consideration of long term parts availability etc.If there's a single part that does the job, I'm buying it. If there isn't, I'm looking for a way to design a new converter using off the shelf components.

author: rob77
author_rank: Super Contributor
timestamp: October 30, 2017, 03:23:36 pm
content: you'll never make it yourself under 1$ , you will hardly get it under $5 (development, testing, compliance, EMC, injection molds.... etc..) .just choose an existing one from chinese manufacturers and swallow the $2-3 pricetagand just my personal opinion: a if a $1-2 difference on the power supply would ruin the profitability of your product then your product is most probably doomed already.

author: Unixon
author_rank: Frequent Contributor
timestamp: October 30, 2017, 09:18:28 pm
content: I thought of making it just a part of layout, not an individually packaged device. So that $1 point refers only to a cost of components.Power bricks we use now are in $2-3 range and make up for 15% to 40% of total cost, since the entire product is intentionally inexpensive.In this low price range even a small addition to component cost eventually makes people wonder what they are paying for when they're seeing selling price

author: orolo
author_rank: Frequent Contributor
timestamp: October 31, 2017, 03:43:17 am
content: A while ago I did a search along these parameters and settled for a Power IntegrationsLNK304.Edit: Forget this. I didn't count in the isolated requirement. Hard to do for less than 1$.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2017, 04:17:18 am
content: Quote from: Unixon on October 30, 2017, 01:42:07 pmThere are numerous solutions for 50-100mA without isolation which work out a lot cheaper than 500mA. However, the overheads in transformer construction to meet the barrier requirements for isolated mains operation means its hard to get much of a cost improvement by dropping from 500mA capacity to 100mA. If you look through the reference designs from the SMPS device makers, you'll find very little below about 500mA that offers a full isolation barrier.

author: ebclr
author_rank: Super Contributor
timestamp: October 31, 2017, 04:22:37 am
content: 5 Pcs for 6.50https://pt.aliexpress.com/item/AC-90-240V-110V-220V-to-DC9V-300mA-5V-100mA-3W-Dual-Output-Switching-Power-Supply/32610714483.html?spm=a2g03.search0204.3.2.dBbvC7&ws_ab_test=searchweb0_0,searchweb201602_1_10152_10065_10151_10130_10068_10344_10345_10547_10342_10343_10340_5620011_10341_10548_10545_10541_10307_10060_10155_5640011_10154_5370011_10056_10055_10539_10538_10537_10536_10059_10534_10533_100031_5730011_10103_10102_10142_10107_10324_10084_10083_10178_10312_10313_10314_10073_5720011_5630011,searchweb201603_25,ppcSwitch_5_ppcChannel&btsid=78b1523e-e890-46d6-b6cf-6704e2b6bb43&algo_expid=1ba01365-c7be-466e-b83c-68a2fddc49bc-0&algo_pvid=1ba01365-c7be-466e-b83c-68a2fddc49bc

author: strawberry
author_rank: Super Contributor
timestamp: October 31, 2017, 11:13:26 am
content: If you are going in 1$ range in chenese SMPS- be ready for:1)bad soldering, (solderbridges, bad joints)2)low quality electrolytic capacitors, (standard electrolytics in switching applications)expected lifespan between 1..3y3)bad PCB layout, bad design, (low creepage between primary and secondary and internal HV circuitry)4)no EMI compliance at all, (EMI choke might not be present) no certification at all5)output voltage overshoot and startup characteristics, (bad overall design (feedback,transformer)and there you can do nothing)6)They wont be all the same, different batch from previous7)there are no guaranteed safe operation within temperature ranges8)high output voltage noise/rippleLong time ago I had bought these cheap 1..2$ electronic ballasts. There were cracks in solder joints after installation. One unit had solder bridge on main electrolytic created unexpected short. These thing didn't last long. SMPS main failure reason are electrolytics, sometimes there is missing circuitry like over voltage clamp in flyback SMPS or RC compensation/oscillation dampers in power amplifiers and so on

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 31, 2017, 11:33:22 am
content: FYI, the old fashioned version isn't much cheaper,https://www.digikey.com/product-detail/en/triad-magnetics/F10-110-C2/237-1557-ND/3986429You might get a transformer close to $1/100s from China, but not under.An SMPS still needs the transformer (a smaller one), but it needs support electronics, too, and assembly, testing and approval.Or, if you're doing the approval all yourself, you might find one that doesn't have any approvals, and try to push it through -- AFAIK, this is expensive for UL/CE testing, so it's going to cost more than $1/unit until you're selling many tens of thousands.Tim