Extreme Low Cost AC/DC PSU   need 0.2A @ 5V isolated. - Page 1
Forum section: electronics / projects

author: mrpackethead
author_rank: Super Contributor
timestamp: July 17, 2015, 02:08:52 am
content: Hi, I'm looking for a reference design for a very low cost Switching supply, it needs to be Isolated, and i need .2A @ 5V..Any suggestions.

author: mmagin
author_rank: Frequent Contributor
timestamp: July 17, 2015, 02:33:55 am
content: I seriously doubt that you can do better than to copy the usual crappy USB charger designs, albeit hopefully with proper safety (2500V isolation in the transformer, enough mechanical strength it won't fall apart on the user, properly rated X/Y caps if used, a fuse, etc.)

author: Berni
author_rank: Super Contributor
timestamp: July 17, 2015, 09:54:29 am
content: Buy a phone charger and take out the guts

author: Lightages
author_rank: Unknown
timestamp: July 17, 2015, 02:55:09 pm
content: Actually better than buying a charger, go to some random hotel with your phone in hand. Tell them you think you left your phone charger in a room and they will bring a box of chargers for you to choose from. Once you have this, take out the guts and install it in a project box with small isolation transformer on the input. If you can't find a small 1:1 transformer, then get two line to 12V transformers and then connect them secondary to secondary and you will have a small isolation transformer.

author: edavid
author_rank: Super Contributor
timestamp: July 17, 2015, 03:36:42 pm
content: He's looking for a design, not a charger

author: Berni
author_rank: Super Contributor
timestamp: July 17, 2015, 04:48:08 pm
content: He did say extremely low cost. Doesn't get any cheaper than a genuine Won Hun Lo micro usb charger, cough up a few bucks and they will send a 10 pack of them your way with free shipping.Tho the isolated part might be debatable with those, since they have a pretty liberal definition of isolated at the good ol Hun Lo co.

author: Lightages
author_rank: Unknown
timestamp: July 17, 2015, 04:50:05 pm
content: Quote from: edavid on July 17, 2015, 03:36:42 pmYes you are right, he asked for a design, not something purchase.

author: kripton2035
author_rank: Super Contributor
timestamp: July 17, 2015, 05:41:02 pm
content: buy one of these :http://www.dx.com/p/isolated-switching-power-supply-module-green-5v-600ma-240410#.Vak9GWZG1Uwthen reverse engeneer it there is quite nothing inside should be easy...or use texas search engine for power supply :http://webench.ti.com/webench5/power/webench5.cgi?lang_chosen=en_US&VinMin=85&VinMax=260&source=AC&line_fsw=50&O1V=5.0&O1I=0.5&op_TA=30

author: edavid
author_rank: Super Contributor
timestamp: July 17, 2015, 06:54:19 pm
content: Quote from: kripton2035 on July 17, 2015, 05:41:02 pmAnd how would you go about sourcing the unmarked IC and transformer?

author: Siwastaja
author_rank: Super Contributor
timestamp: July 17, 2015, 07:02:05 pm
content: Getting a properly designed brand charger and reverse-engineering it would make a lot of sense, as you will learn practical things that are lacking from the simplest designs - especially related to safety and EMI. Ebay/DX chargers could give wrong ideas, or nothing extra compared to simplest flyback example design you can find on Google image search for schematic, although that would still be a good starting point.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 17, 2015, 07:05:19 pm
content: Hi,Look at the offerings from Power Integrations:https://ac-dc.power.com/products/tinyswitch-family/tinyswitch-4/They may have lower power products but this is a start.Jay_Diddy_B

author: kripton2035
author_rank: Super Contributor
timestamp: July 17, 2015, 07:18:24 pm
content: Quote from: edavid on July 17, 2015, 06:54:19 pm99% chance the IC is a UC3842 ...