Isolated DC/DC converter - Page 1
Forum section: electronics / projects

author: jb79
author_rank: Contributor
timestamp: February 12, 2015, 04:31:50 pm
content: Hello!I'm searching for a reasonably priced isolated DC/DC converter (about 5-6€) for a hobby project with the following specification:Input voltage: about 10-18V, a bigger range would be ok too.Output voltage: 5V fixedPower: about 3WSize/technology: as small as possible, SMD or wired partsI've found a part with this specification in China (aliexpress): WRB1205CS-3W (about 5,6€/piece), but a reseller in Europe would be better, because there are no customs duties within the European Union.Amount: several ten pieces up to 100.

author: bktemp
author_rank: Super Contributor
timestamp: February 12, 2015, 04:59:52 pm
content: Meanwell SCW03A-5

author: Jeroen3
author_rank: Super Contributor
timestamp: February 12, 2015, 06:41:39 pm
content: You might find some Recom (unregulated) modules on eBay. Within europe.

author: DanielS
author_rank: Frequent Contributor
timestamp: February 12, 2015, 07:30:43 pm
content: Not quite what you are looking for since these top out at 2W but TI has a few nice little monolithic packages for isolated DC-DC applications:http://www.ti.com/lsds/ti/power-management/1w-2w-miniature-module-products.page

author: necessaryevil
author_rank: Regular Contributor
timestamp: February 12, 2015, 09:42:41 pm
content: What do you want to do with the converter? Do you need an stabilized output voltage? Do you need multiple outputs?By the way, I don't know what the rules are in Austria, but does the tax/duty apply on your products? Here in the Netherlands no additional charges such as taxes/vat/duty apply if your imported goods don't exceed a certain value (I think it is about €50)

author: DanielS
author_rank: Frequent Contributor
timestamp: February 12, 2015, 10:06:53 pm
content: Quote from: necessaryevil on February 12, 2015, 09:42:41 pmWell, OP is looking for tens to 100+ converters at ~6EUR a pop, so the bill would be around 600EUR, well beyond most country duty-free range.In Canada, tax-exempt imports are $20 for commercial and $60 for gifts. (I'm in the process of researching the import/export process over here to help two people from the USA send me gifts. Quite annoying how it seems like neither the border agency or CanPost is bothering to put links to the actual forms or a page where they can be found.)

author: jb79
author_rank: Contributor
timestamp: February 13, 2015, 03:28:56 pm
content: Hello!There are some 5V relays, 74HCTs, analog and 3,3V ATXMEGA processors (3,3V low drop regulator that uses the 5V as input), so the 5V should be regulated (+/-10%).I've had a look at the TI converters but there are 2 problems: 1.) Only 2W, that might be not enough reserves, 2.) It looks like they only produce for very small input ranges (5V, 12V, 24V, all +/-10%). My input voltage will be in the range of 15-17V, so that would require a 12V preregulator too. A simple LM7812 will produce something between 1,5-2W heat when the full 3W of the converter are used. I'm looking for a solution that requires only external capacitors, maybe a small inductor and a polarity protection diode for the input.In Austria any import not from countries within the European Union are only free up to 22€ (value of goods + shipping).Between 22€ and 150€ we have to pay a import sales tax (normally 20%)Over 150€ you have to pay import sales tax and customs duties.

author: dmg
author_rank: Regular Contributor
timestamp: February 13, 2015, 05:02:43 pm
content: I've succesfully implemented what you want with an LT3575, but desgined to deliver about 8 W at 5V from a 15V supply but it would do more than 3W from less than 10V and would work above 20V too.LT3575 is one of the fastest switching IC's for this application out there and we also had size constraints. This IC doesn't require an optocoupler for feedback but the required trasformers are still big (1,5 cm^3 or so, even SMD ones) and it also needs a big rectifier diode and relatively large capacitors. Overall the thing fitted in about 5x3x2cm and worked very well, but keep in mind that the transformer will be the largest part of it.Also total cost of the PSU for 1 unit was about 20€ because both LT3575 and are expensive parts.Maybe the cheapest and smallest soultion for your application would be using an integrated module, giving that power requirements aren't that big in your case and there might be some options available.