Looking for small switcher with (apparently) unusual input rating - Page 1
Forum section: electronics / projects

author: AussieBruce
author_rank: Regular Contributor
timestamp: August 20, 2022, 05:04:27 am
content: I need a small switcher PSU board to generate 12vDC (isolated) at about 1A, the only input available is a 24Vac 50Hz supply. If I rectify then filter it, I get around 35volts, by voltage doubling that becomes around 70, with more ripple. There are heaps of switchers accepting much lower voltages, and also DC inputs between 35 and 70v, but that's really marginal for a rectified/filtered 24AC supply. I don't want to use a linear preregulator, much prefer to feed the switcher with 35Vdc directly.I did look at low loss variants such a stepdown tranny or autotranny (cost and space problems), and choke input, but at low output current that runs the risk of overvoltage.Have done a fair amount of hunting around, is anyone aware of a source of switchers that will generate what I need, with an input range comfortably around 35vDC?

author: AussieBruce
author_rank: Regular Contributor
timestamp: August 20, 2022, 05:10:50 am
content: Sorry, tried to remove but couldn't. Have come up with a solution.

author: JoeyG
author_rank: Regular Contributor
timestamp: August 20, 2022, 07:45:47 am
content: Pre-made "brick" DC-DCSCW12C-05For volume OEM designMIC28512https://www.microchip.com/en-us/product/MIC28512Up to 75V input range and up to 2AMPsOr a moduleMIC28304http://www.microchip.com/mic28304

author: connectTek
author_rank: Regular Contributor
timestamp: August 20, 2022, 09:14:38 am
content: Can you share your solution, I'm in the same boat.Thanks

author: mariush
author_rank: Super Contributor
timestamp: August 20, 2022, 09:52:51 am
content: Rectify to DC then pass to a dc-dc converter with isolationExamples :https://www.digikey.com/short/79p2vfrn(further filtering to see only those capable of rectified 24v may be required)

author: connectTek
author_rank: Regular Contributor
timestamp: August 20, 2022, 06:13:59 pm
content: Need max 48v input as most industrial power 24vac supplies can be as high as 28vac, about 40vdc rectified plus some headroom for saftey.

author: artag
author_rank: Super Contributor
timestamp: August 21, 2022, 04:22:04 pm
content: Look for converters intended for PoE - one reason these used to be expensive is that typical converters couldn't handle the 48V PoE line. I presume there are more available now it's more widely used.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 23, 2022, 11:50:13 am
content: How about using a 24 to 240V or 120V Transformer and a regular AC-DC supply?Cheap enough.https://www.jaycar.com.au/12v-0-12v-20va-toroidal-transformer-low-profile/p/MT2084

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 23, 2022, 01:25:20 pm
content: I don't know about general availability -- or cost for that matter, heh -- but have seen similar ratings show up in train (rolling stock) equipment. Electrical buses are often 12, 24 or 120V, with various tolerances on each (like the '24' might include min. 22V from lead-acid backup, up to 36 or 48V or even a bit more, for flexibility, or accommodation of transients).Tim

author: Terry Bites
author_rank: Super Contributor
timestamp: August 24, 2022, 05:36:53 pm
content: Just for "fun". I Ćuked (cringe) some values into Webench power designer>>>>Uses an off the shelf coil for a change. A bit of perf board, job done probably....https://www.ti.com/design-resources/design-tools-simulation/webench-power-designer.html

author: langwadt
author_rank: Super Contributor
timestamp: August 24, 2022, 05:50:35 pm
content: https://www.tracopower.com/int/series/thd-12wi