# Isolated Power Supply Modules

I originally planned to use ISOW7841 digital isolator with Isolated power to interface part of my circuit. But Having the power and signals on one IC, is causing me problems. This is because I need to have a 5v on my isolated circuit, and the digitals signals are on 3.3v logic. Meaning For me to have 5viso i have to have 5vin meaning that the digital signal level would also be 5v and therefor i have to place level shifters on both sides of the isolator.

So I decided to split it into signal and power. So that the digital signals can be at 3.3v while still having the 5v power. As for digital signals it pretty easy to find an IC like the ISO7741. What im having trouble looking for is the Isolated power IC. What would they be called using terms like power isolators just brings me back to digital isolators the category ISOW7841 belongs Or being brought to those really expensive modules. My load is not high and will consume less than 100mA at 5v.

• It seems your question has nothing to do with signal isolation, despite many words to that matter, because your isolated circuit for some reason requires supply voltage different from signal voltage. If you remove all that irrelevant information what is left is shopping question (which are off-topic here) "where to get cheap isolated DC-DC?" Jun 21 '20 at 15:34
• Having said that, you have to define what is "really expensive" for you. Even a brief search on digikey gives for example $2 RFM-0505S. Add to that$0.50 LDO and a cap and you are done. And for the fraction of cost of the signal isolator chip with built-in power transfer. Jun 21 '20 at 15:40
• @Maple I really mean to ask what are their proper terms. Because the ones i found specd close to the ISOW7841 cost upward of 30$, the ISOW7841 is a 10$ chip. Thats why i thought im missing something. What search key did you use? Jun 21 '20 at 16:42
• I clicked "Power Supplies - Board Mount" in main product index, then "DC DC Converters" sub-section. After that just select all "isolated" types and you'll get yourself 242 thousand models to choose from Jun 21 '20 at 18:34

Take a look at the SN6501 and, if it isn't what you need then you can use the keywords in its description to find an alternative.

It's used quite extensively for isolating bus power on such systems as RS485 repeaters: -

As for isolation, the transformer shown above will need to have the requisite insulation properties between primary and secondary. See this extract from the above data sheet: -

The data sheet also might provide you good circuit ideas like this: -

• A really good recommendation since my isolated section has ADC and the datasheet has the complimentary parts listed. I did found some all in one IC but their current output is a tad lacking. Thank you very much for the recommendation good sir. Jun 21 '20 at 16:54
• Quick question though what does that column labeled "LDO" mean ? Those tagged with yes must have LDO's attached to them ? Jun 21 '20 at 17:02
• @Jakequin I haven't looked in detail but that's my conclusion. Jun 21 '20 at 17:29

Take a look at the MORNSUN isolated DC/DC converters, have used many and works great. Take a look at their product page for example: https://www.mornsun-power.com/html/products/4/dc-dc-converter.html

There are other brands however more expensive or never tried.

• They look nice little devices. Jun 21 '20 at 16:56
• They look great to bad though i could not find their parts that i liked on digi-key :( Jun 21 '20 at 17:24
• @Jakequin There are also other brands, like Murata however a way more expensive. Search on "isolated DC DC". These MORNSUN variants, you can find them on Aliexpress. Jun 21 '20 at 21:38
• Yes ! there are great selection, I liked this one. I will have to research more which is better than the one Andy aka suggested. Jun 22 '20 at 12:03