Isolated Power sup. mod. Connecting input and ouput Gnds - Page 1
Forum section: electronics / projects

author: electronx
author_rank: Regular Contributor
timestamp: December 27, 2023, 05:49:38 pm
content: I need a converter module that outputs +15 -15 Volts to feed the opamps. My input voltage is 24V.I found that UWE1215S-3WR3 for this application. UWE1215S-3WR3 datasheet--------------------------------------------------------------------------I know that normally the input and output gnd pins must be completely separated from each other in order to fulfill the isolation function. know that if I connect the gnds of an isolated power supply, the isolated situation will disappear, but I wonder if I will have a problem if I connect the input gnd and the output com pin of a dc dc isolated power supply.Is it okay?can i use it like this?

author: wasedadoc
author_rank: Super Contributor
timestamp: December 27, 2023, 06:26:12 pm
content: Yes.

author: electronx
author_rank: Regular Contributor
timestamp: December 27, 2023, 07:51:38 pm
content: If it only gave +15 V output, I could be sure of this, but -15 V output confuses me. If there is a system inside the module that gives dc dc positive input and negative output, I do not think there will be a problem, but I do not know what is going on in the background.

author: CountChocula
author_rank: Unknown
timestamp: December 27, 2023, 08:15:46 pm
content: The output is isolated from the input, so this will work fine—no need to worry about the negative voltage.Incidentally, Mornsun also makes non-isolated buck modules that are pin-compatible with traditional 78xx linear regulators and can be used to derive both positive and negative voltages from a single rail. They only have a single output (so you need two modules to generate +/-), but if you don't need isolation they are cheaper than the module you chose and work great.

author: magic
author_rank: Super Contributor
timestamp: December 27, 2023, 08:19:26 pm
content: It should be OK - if the converter can work with any output GND potential, it will also work with output GND equal to input GND.Internally it must be using a transformer and some configuration of output winding(s) and diodes which produces a voltage negative with respect to output ground in addition to a positive one.

author: electronx
author_rank: Regular Contributor
timestamp: December 27, 2023, 09:20:22 pm
content: https://www.digikey.com/en/products/filter/dc-dc-converters/922?s=N4IgjCBcpgHAzFUBjKAzAhgGwM4FMAaEAeygG0R5YAGeAdjpCKtrticpvoE4QBdIgAcALlBABlYQCcAlgDsA5iAC%2BRAKx1E0EKkiZchEuRAAWOibBhGRMxcscw3TXWr8hoyBOnylq8GoAmNSQddGx8IlJIChc1J1ciMFo1E0QiIICTdnTYFzTTeDM2DkKggDYSkyDsyiqUyoyOE24AgLKE2oC6YKIXIprSugrmMvbrWrjeZhpukpnhyiduCGYlhfhuGhXF2DAFrPgNHtM4jSbT45M4su2r7lHz%2B5qweGoLDpe3gO297g2F34magBByaTIAsFmUHwTLPMH1RLw45WCywZHmOBTEB0MBdQ5NExlNTUDomQnEkHpahDeDbVrLAIdelgMkcZnEgllVLjZntNmvahwNnNWBODhDNREgnLFkOWjtZHJKpyqhS3oUtTPPbErEslj5MBqNRwA2wInUZFOehMyxohatG6ZflGmj83JUBywLpdBws2JuEAiMSSWSKFSJQIVbS6fQRIzRcBKg2vKoggSBjxeUO%2BIgAWhB0ag0gAroYohRgnxlNWgAThanks for your answer. If you examine these digikey products, you can see that there are single non-isolated modules (they do not have two outputs). Depending on the connection type, they can only output -15 or +15.For +15 Volt fixed output range, the input voltage range is 20-36V (The voltage I will use is 24 V) this is okay.The problem is that the input voltage range for a -15 volt fixed output is 8-18VVoltage input range for negative supply is insufficient. If you have any other suggestions, please let me know.By the way, is the Mornsun 78xx series you mentioned one of these?

author: electronx
author_rank: Regular Contributor
timestamp: December 27, 2023, 09:26:59 pm
content: the gaptec brand also offers + and - 15 configurations, and again, the input range does not include 24 volts. Maybe I can draw it from 24 volts to the input range with the help of an ldo, but having too many converters does not seem healthy.

author: CountChocula
author_rank: Unknown
timestamp: December 27, 2023, 09:32:18 pm
content: I was actually looking atthis module, but it also doesn't support your input voltage. Sorry—I missed that requirement.

author: ArdWar
author_rank: Frequent Contributor
timestamp: December 28, 2023, 12:25:29 am
content: Quote from: electronx on December 27, 2023, 07:51:38 pmSmall isolated converter like this are usually using push-pull topology. It can work with positive, split, or even negative output. Well, the output should be floating so not like there's any difference between them.Check TI's SN6501 or SN6505 if you want to know how it works. Mornsun also sell their own version of it, so it won't be surprising if this module is just a ready to use version of that.

author: electronx
author_rank: Regular Contributor
timestamp: February 23, 2024, 08:13:43 pm
content: I just connected the output com pin to the input Vin- pin for the dc dc converter, which has an isolated +-5 Volt output from the recom. It works very stable (at least it didn't burn). If I have time, I will look at the changes in ripple and connect the load.