Lowest cost 240Vac to 5Vdc 1W (Isolated and non-isolated) power supply solutions - Page 1
Forum section: electronics / projects

author: Jester
author_rank: Frequent Contributor
timestamp: January 26, 2017, 02:07:06 am
content: Three obvious approaches to anon board240Vac to 5Vdc 1W power supply.1) Linear with a mains transformer2) Off line switcher for example LNK30x or TNY26x3) On board module; Recom, CUI etc.Other considerations:- does it need to meet EMC compliance- does it need to pass surge testing (fast transient etc)- does it need to be isolated or can the circuit ride on the MAINSTo clarify this particular solution must be:- On board (wall-warts need not apply)- Powered from 240Vac- manufacturable in quantityThis will be mounted outdoors in a waterproof NEMA case and will be powered from 240Vac. There will NOT be a power receptacle anywhere near this, just a couple hundred feet of #12AWG from a 15A fused 240Vac circuit.So if you have a favourite circuit that you would like to share please do.Edit added text in italics for clarity

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 26, 2017, 02:18:10 am
content: For small quantity, you won't get any cheaper than cheap but decent USB power supplies. Just take it apart and use the module in your own device or use as-is.

author: Jester
author_rank: Frequent Contributor
timestamp: January 26, 2017, 02:44:30 am
content: Quote from: NiHaoMike on January 26, 2017, 02:18:10 amI need a solution that can be manufactured in batches of 100 to 1000

author: jeroen79
author_rank: Frequent Contributor
timestamp: January 26, 2017, 03:33:20 am
content: The thread title says "lowest cost".With an external off the shelf power supply you just need to add a USB or DC socket to your's product's case.No need to bring in mains AC into the product itself, no need to design, test and certify for safety in that aspect.Just buy a batch of wall warts.

author: Jester
author_rank: Frequent Contributor
timestamp: January 26, 2017, 03:58:34 am
content: Quote from: Jester on January 26, 2017, 02:07:06 amTo clarify this particular solution must be:- On board (wall-warts need not apply)- Powered from 240Vac- manufacturable in quantityThis will be mounted outdoors in a waterproof NEMA case and will be powered from 240Vac. There will NOT be a power receptacle anywhere near this, just a couple hundred feet of #12AWG from a 15A fused 240Vac circuit.

author: ondreji
author_rank: Contributor
timestamp: January 26, 2017, 05:00:45 am
content: Have a look at this one:http://www.hlktech.net/product_detail.php?ProId=54-5V / 3W. Manufacturer sales then for $2.50. I bought couple for $1.50-ish (from Aliexpress)...

author: Jester
author_rank: Frequent Contributor
timestamp: January 26, 2017, 01:26:10 pm
content: Quote from: ondreji on January 26, 2017, 05:00:45 amYes, these do look promising, I have some on order. I will Hi-Pot one to see if I can break it.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 26, 2017, 01:41:20 pm
content: If you don't need isolation the LNK30x devices are pretty cheap - maybe a dollar or so BOM cost

author: mrtn
author_rank: Contributor
timestamp: January 26, 2017, 02:37:11 pm
content: Quote from: Jester on January 26, 2017, 03:58:34 amThe FSL306LR seems to be one of the less expensive direct off-line switchers.http://www.digikey.com/product-detail/en/fairchild-on-semiconductor/FSL306LRL/FSL306LRL-ND/4963483

author: Jeroen3
author_rank: Super Contributor
timestamp: January 26, 2017, 06:55:35 pm
content: Calculate if you can afford the engineering timefor your own design when compared to vigortronix modules. Which are like <€5 euro for 1W 5V per 100 pcs. Possibly less when ordered directly, or even cheaper when looking at taoboa or similar. However quality control comes down to you then.http://www.vigortronix.com/smpspcbpowermoduleACDC.aspxIf I want to develop a circuit like this I will need at least:- A few weeks of time to develop the product, assembly guide for enclosure outsourcing.- Some temperature testing (say -20 to +60).- Two prototypes. It never works first try.- Possibly rf interference, EFT and conducted interference testing, depends on regulation fetish of the customer. In europe you can just put on CE and sell it. How is that in the US?- The inevitable "I have no idea what I'm doing" loss of time since I've never build such a circuit from scratch.Your own circuit might only become profitable when you add many zero's to the quantity.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 26, 2017, 07:25:06 pm
content: Quote from: Jeroen3 on January 26, 2017, 06:55:35 pmTrue, however if you already have a PCB design to do anyway, dropping in a reference design for the LNK30x may not be a lot more effort, and may reduce potential risks of leadtime and/or future availability of a module from an obscure manufacturer.As regards approvals, the module manufacturer could change their design or obsolete it without notice - a much lower risk with a chip from an established manufacturer.

author: mariush
author_rank: Super Contributor
timestamp: January 26, 2017, 08:22:32 pm
content: The most hassle free would probably be linear transformer + bridge rectifier + capacitor + linear regulator / switching regulator.In 100+ quantity, you can get suitable transformers for less than 3$ each.For example, TME.eu has ready to solder on pcb transformers starting from 2.3VA and up, from about 1 UK pound each if you buy 100 :http://goo.gl/akrJUwIt would safer though to go with something like at least 3VA or more to allow for variation in input voltage which will also affect the output voltage of the transformer (you're saying device will be powered from mains with tens of feet of cable, there may be some voltage drop on the cable)The bridge rectifier / diodes + smoothing capacitor + linear regulator / dc-dc converter would cost less than 1$ and you don't have to worry about passing various regulations about EMI , RF etc , it would work on wide range of temperatures etc .. you can panelize these and just leave room (footprint) on pcb to solder the transformer at the end.

author: DBecker
author_rank: Frequent Contributor
timestamp: January 26, 2017, 09:09:01 pm
content: I like the LNK30x parts, especially for low power supplies. But a proper protection network and input filter (MOVs, X1/Y1 rated caps and a safety-rated resistor) is annoyingly expensive in small quantities.For an isolated switching supply, finding an inexpensive off-the-shelf transformer is the challenge.Line-frequency transformers have challenges meeting energy-efficiency standards, so I pretty much rule them out even for prototypes.

author: tszaboo
author_rank: Super Contributor
timestamp: January 26, 2017, 11:04:50 pm
content: Quote from: mikeselectricstuff on January 26, 2017, 07:25:06 pmIt might be cheaper, but if the batch will be few hundred, and the alternative drop-in power supply is 3 EUR, that doesnt leave a lot of wiggle room for design. Just getting a single part do everything, tested and reliable is worth more, than doing 2 days of design, 2 days of testing, to save say, a hundred bucks.

author: Jester
author_rank: Frequent Contributor
timestamp: January 26, 2017, 11:45:10 pm
content: IMO this is turning into a great thread, thanks to all the comments.Good to see another OTS option (vigortronix modules) - thanks Jeroen3I was not aware of TME, great search engine, too bad we don't have one in USA or Canada - thanks mariushGreat point about the "extra components" by DBecker, the cost of all the extra stuff is actually what got me started on this thread. That being said some of the OTS modules will likely need additional filtering and protection to pass FCC and surge testing (if that's required)Never thought about the SCR approach - thanks blueskull