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

author: akis
author_rank: Frequent Contributor
timestamp: November 23, 2013, 10:22:26 am
content: I have bought some cheap ammeters off China, but they require independent power supply. In the past I used similar devices by winding a few extra turns around a the main toroidal transformer, so as to get the required, isolated voltage.In my current project I do not have a toroidal to tap, so I need something like a "DC to DC isolating converter". I have looked up the available ICs and there aren't that many: most DC-DC converters are non-isolating, ie they share a common ground.I was thinking of making my own HF oscillator --> small transformer --> bridge+filter --> isolated voltage. But this requires a lot of components. It would need: op-amp, 6 resistors, 2 caps, external pass transistor, transformer, 2 or 4 diodes (bridge), filter cap.Is there a better way to do this?Thanks

author: ovnr
author_rank: Frequent Contributor
timestamp: November 23, 2013, 10:30:44 am
content: Just buy an isolated DC/DC module? I've been using someRK-0515Smodules, which work fine for my needs. I'm sure there's something out there that'll work for you.Just stop by Digikey andlookfor something suitable.

author: Psi
author_rank: Super Contributor
timestamp: November 23, 2013, 11:05:09 am
content: You can get pretty cheap 5V in 5V out modules which are isolatedhttp://www.digikey.com/product-detail/en/RBE-0505S/945-1653-5-ND/3461634

author: David_AVD
author_rank: Super Contributor
timestamp: November 23, 2013, 12:34:58 pm
content: As the other have said, off the shelf isolated DC-DC converters are very common and not expensive. Just be away that the cheaper ones tend to be "semi regulated" and may also have a higher minimum load requirement.

author: Marco
author_rank: Super Contributor
timestamp: November 23, 2013, 02:05:13 pm
content: Quote from: akis on November 23, 2013, 10:22:26 amYou didn't search right then, the most common are the ICs supporting flyback and there are a huge amount of those. Probably not worth it to do it yourself with the integrated modules available.

author: akis
author_rank: Frequent Contributor
timestamp: November 23, 2013, 02:59:52 pm
content: I have found these which seem to be what I need: Murata MEV1 series, XPPower IA and IQ Series 1W. These are DC to DC *and* isolating, ie they have 4 pins, not 3.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 23, 2013, 10:42:00 pm
content: Have you tested your gauges? Because the cheap ones I bought from China don't need an isolated supply.

author: Monkeh
author_rank: Super Contributor
timestamp: November 23, 2013, 10:46:43 pm
content: I use these for such meters:http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1818325There are a variety of input voltage ranges available. I strongly doubt you need the 3kV versions.Quote from: AmmoJammo on November 23, 2013, 10:42:00 pmSome do. I think it's fair to assume he's found out the hard way.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 23, 2013, 10:53:22 pm
content: Quote from: Monkeh on November 23, 2013, 10:46:43 pmMight be cheaper and easier to just get some meters that don't need isolation though

author: Monkeh
author_rank: Super Contributor
timestamp: November 23, 2013, 10:55:03 pm
content: Quote from: AmmoJammo on November 23, 2013, 10:53:22 pmI doubt it's cheaper to get another decent meter(three wire toys from eBay need not apply)than it is to buy an off-the-shelf DC-DC module.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 23, 2013, 10:56:20 pm
content: Quote from: Monkeh on November 23, 2013, 10:55:03 pmAh, his were ammeters, not volt meters anywayI think we need to know specifically what he has, they're probably ebay spec anyway.. lol

author: Monkeh
author_rank: Super Contributor
timestamp: November 23, 2013, 10:57:10 pm
content: Quote from: AmmoJammo on November 23, 2013, 10:56:20 pmI'm going to take a wild shot in the dark based upon prior experience: ICL7106/7 single-supply meters.