Simple(?) 240V AC - 5 V DC Circuit - Page 1
Forum section: electronics / beginners

author: frontispiece
author_rank: Newbie
timestamp: September 30, 2012, 11:23:24 pm
content: Hi! I've got a Mornsun LD03-10B05 3W transformer, which should be dead easy to set up & run, but for some reason, I've got it connected to mains and I'm getting 0V from the DC output! I've got L connected to L, N connected to N, the right cap across the cap pins, and nothing coming out.I've attached the RS model (datasheet on the page) and a photo of my problem below, anyone see what I'm missing?The Part:http://int.rsdelivers.com/product/rs/ld03-10b05/power-supply-encapsulated-pcb-mt-5v-3w/6675760.aspxThe Datasheet:http://docs-europe.electrocomponents.com/webdocs/0ce2/0900766b80ce25da.pdfMy Circuit (0V at the output..)(Original resolution)Thanks if you can spot what I'm missing!

author: Astroplio
author_rank: Regular Contributor
timestamp: October 01, 2012, 12:52:37 am
content: Show a better picture of the module and the soldering you have done. There might be some shorts...Try putting some load, a small DC motor or a resistor+LED.C3 is rated for 400V? I see you have 3 caps there, what's their specs, note 5 says you don't need it if your input is 160-264VAC, what is your input?

author: vk6zgo
author_rank: Super Contributor
timestamp: October 01, 2012, 01:48:17 am
content: I am very concerned about you using this thing as a standalone supply.I think the intention is that this device is to be built into equipment which needs to obtain a "floating" 5V from the mains,with the whole unit double insulated.Even in that case,it is very suspect,as the clearance between the mains input tracks on the board is way too small for safety.Are you sure the two mains connections are correct,as it is usual to have the A & L connections separated either by non metal sections,orseveral"dummy" tracks which do not go anywhere,but help to separate the two mains inputs?I don't see any mains earth on your circuit,or did I miss it?You may be taking the utmost care,but your picture looks downright scary!

author: IanB
author_rank: Super Contributor
timestamp: October 01, 2012, 02:01:05 am
content: If you compare the pictures and wiring diagrams on the datasheet, the device pictured by the OP doesn't look anything like. It's a completely different package.The datasheet actually does show L and N widely separated, and the usage examples also show an earth connection with a Y capacitor.I'm confused about exactly what kind of device is shown in the photo in the first post?

author: Monkeh
author_rank: Super Contributor
timestamp: October 01, 2012, 02:22:36 am
content: Quote from: IanB on October 01, 2012, 02:01:05 amIt doesn't, see page 4 for the actual layout.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 01, 2012, 02:28:20 am
content: It seems I blamed the manufacturer for the poor clearances on the board,but now,having looked at the spec sheet,I realise that you have fitted it to a simple "protoboard" or similar.These things are insulated for around 24V or so--they are a definite "NO-NO" for 240V mains!!!!Desolder the thing from the board,& make direct (good,well insulated) connections to the device.By the way,are you sure you have mains input to the thing?Don't measure it directly,you will probably short it out!!Unplug your power cord.& measure continuity from the pins of the mains plug to the board.P.S. Read the next thread down (about Variacs) to get an idea about how seriously people on this forum take Electrical safety!

author: frontispiece
author_rank: Newbie
timestamp: October 03, 2012, 08:14:46 am
content: Thank you all for your warnings! I desoldered from the protoboard right away for proper insulation.However, even with L&N pins individually soldered & insulated by heat shrink, as I'm in the UK with (L)ive, (N)eutral and (E)arth wires - I'm still wondering where I should properly be connecting the Earth wire?As per @Astroplio's suggestion - I did try a load across it before reading these warning messages and desoldering the thing, and it didn't draw any power.@vk6zgo, would you mind explaining if a "floating" 5V would make this unsuitable? I see it's rated for 3W so I figured I could run a 5V servo from it, am I incorrect? To be clear, I'm not just running the servo, just looking to determine why I'm not able to get any power from this at all when (to me), it looks as though it should be able to supply 3W @5v.Thanks again for the cautionary warnings!

author: vk6zgo
author_rank: Super Contributor
timestamp: October 04, 2012, 01:36:16 am
content: Quote from: frontispiece on October 03, 2012, 08:14:46 amDid you double check your power cord for continuity?If you are getting 240V to the appropriate pins,& zilch out of it,it seems like you have a faulty device.Do you have anybody you can take this thing to in person?IIt is quite hard for us to diagnose "remotely".

author: frontispiece
author_rank: Newbie
timestamp: October 08, 2012, 10:53:25 am
content: Thanks, it's working!So to anyone reading this while working on a Mornsun themselves, looks like the L and N pins just needed to be sufficiently separated and insulated, and this is a dead easy transformer to use!I still can't figure out why there's a "no connection" pin ... maybe just for solidly soldering into a PCB? But it's working, thanks for the help.