Specifying custom transformer to be built in China - Page 1
Forum section: electronics / general

author: chimera_786
author_rank: Regular Contributor
timestamp: July 14, 2018, 02:59:26 pm
content: Hello!I am developing a sensor-centric design which will need to run off mains voltage. Its going to be an "install and forget" solution and its installed in regular wall outlets. I have plans to commercialize it but that's long ways down the road. For now, I am at the concept stage.Naturally, this sensor and the supporting circuitry needs power (i budgeted around 5W @ 5VDC) and it can be derived from AC mains source. I am located in the US but decided to accept universal ac input range (85 to 265VAC) at 50/60 Hz. I have already decided on the SMPS IC (with integrated SW) i plan on using and have figured out that UL60950-1 would apply to me. Since this has become an ac/dc converter, I will need a high frequency transformer to process the power (flyback topology) and have done back of the envelope calculations for the specification.So, with this stated, here is why I am posting here:1- Has anyone ordered custom split core transformers (or even COTS transformer) from China (through alibaba)? If so, how did you got about preparing the technical datasheet such that the end product conformed to the safety requirements for the UL60950-1.As an example, how did you specify the insulation requirements for the transformer? Did your chosen production house already know what insulation and how much of it to use etc.2- I'd be happy to outsource this SMPS design to a design house in china (i'll give them PCB outline etc) but so far, I have not been able to find a design house. If anyone has any idea how to go about it, i'd be more than happy to go that route.Designing a SMPS processing mains AC into DC isn't exactly a complicated exercise but creating specifications for the transformer and having a production house in china conform to it is challenging, especially when you're sitting on the other side of the world.Any response addressing 1 and/or 2 is welcomed!Thanks!

author: chris_leyson
author_rank: Super Contributor
timestamp: July 14, 2018, 05:08:54 pm
content: These guys are really good and they have a factory in China.http://erhk.hk/en/You might be looking at an EE16 sized core and as it's UL60950-1 for IT equipment then the creepage and clearance distances are relaxed a little bit. If you need to pass fast transients at >2kV I wouldn't recommend Power Integrations, I've had nothing but trouble.

author: jmelson
author_rank: Super Contributor
timestamp: July 14, 2018, 08:09:55 pm
content: Why on earth would you design your own power supply when you can get safety certified wall-wart type supplies in a wide range of voltage and power?Jon

author: DerekG
author_rank: Frequent Contributor
timestamp: July 15, 2018, 12:44:59 am
content: Quote from: chimera_786 on July 14, 2018, 02:59:26 pmBelow is the way I would go. Already has UL & CE certifications. Just ask the manufacturer for a copy of the approvals.5W, 5Vdc, PCB mounting, fully enclosed, miniature & good value. Currently these work out at US$2.66ea in lots of 20. They will be even cheaper if you have the volume to buy from the manufacturer direct. For volume, take a look at the offerings onwww.alibaba.comhttps://www.aliexpress.com/item/20-pcs-lot-HLK-5M05-AC-DC-220V-to-5V-5W-mini-power-supply-module-intelligent/32891647785.html?spm=2114.search0104.3.14.6f0412a3asU5JQ&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10130_10068_10342_10547_10343_10340_10548_10341_10696_10084_10083_10618_10307_10131_10132_10133_10846_10059_100031_10103_10624_10623_10622_10621_10620,searchweb201603_44,ppcSwitch_5&algo_expid=0afe9a3c-2aca-4fb9-9f3b-d5ca1429514f-2&algo_pvid=0afe9a3c-2aca-4fb9-9f3b-d5ca1429514f&transAbTest=ae803_2&priceBeautifyAB=0This is but one seller. There are lots of others on Aliexpress & eBay too.

author: chimera_786
author_rank: Regular Contributor
timestamp: July 16, 2018, 02:36:49 am
content: @jmelsonThe housing for the product I am considering to work is limiting what i can throw int here. A wall wart,as you suggested, will not fit in my enclosure (even if I just use the populated pcb from wall wart).@ DerekGYes. This self contained power module might work well for me. Although, I have used something similar in the past and the output regulation was terrible, not to mention the hysteritic control messing up the ripple profile. I ended up using a LDO at the output of such module and relied on the PSRR of the LDO to manage the ripple magnitude.@chris_leysonI sent you a PM, seeing that you were online at the time of this post. I basically asked if you had used them and what was your experience with them. The problem I am facing is coming up with clear and concise datasheet for the transformer I want designed. I'll probably need help on defining the safety items in the transformer (margin tapes, insulation thicknesses, winding techniques etc...)

author: DerekG
author_rank: Frequent Contributor
timestamp: July 16, 2018, 02:47:48 am
content: There are un-housed units as well as the housed one I linked to 2 posts up.You are unlikely to gain much space making your own un-housed switch mode power supply.An example:https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20180715184205&SearchText=5w+5V+power+supplyAgain, just look for one that already has the UL & CE certifications already done.If these don't suit, spend your US$20K on certifications & 200 hours in sourcing the components, design & proofing.I don't see that there are any other options available to you.

author: chimera_786
author_rank: Regular Contributor
timestamp: July 16, 2018, 03:06:01 am
content: @ DerekGYou're right. The unhoused power supply solution would be a pain to install on the pcb (precluding it from a P/P machine for quicker installation).I'll definitely consider using these modules for ease of implementation..

author: flasonsmts
author_rank: Contributor
timestamp: July 20, 2018, 10:08:04 am
content: I don't think the certification will spend so much , there's many company that can offer you a price around 300USD for each kind UL or CE certification.