Any split +/-15V modules out there? - Page 1
Forum section: electronics / beginners

author: GreyArea
author_rank: Contributor
timestamp: August 19, 2020, 07:09:25 pm
content: I have a module that I'd like to experiment with that has a split rail requirement of +/-15V and I haven't been able to find a (cheap) supply module which has these kinds of outputs.I was wondering if anyone could advise on a solution - I'm not averse to "rolling my own" but would need book recommendations from a beginner perspective on (negative rail) power supply design. While it would be an interesting exercise, and something I'd like to do, I really want to focus on the module if possible.TIA - Matt.

author: LateLesley
author_rank: Frequent Contributor
timestamp: August 19, 2020, 07:16:59 pm
content: It depends what type of current requirement you have. If it's low power, you could use a couple of these modules to make a low current split rail supply from a 5V input.https://www.ebay.co.uk/itm/DC-DC-Converter-5V-to-15V-1W-isolated-single-output-New-Qty-1-SPECIAL-OFFER/123699311635?hash=item1ccd0db413:g:itgAAOxyrP9RZ3uiYou can also get dual output modules for higher current requirements.https://www.ebay.co.uk/itm/UK-Dual-Output-Variable-PSU-DC-DC-20W-Positive-Negative-Step-Up-Down-Boost-Buck/303536235236?hash=item46ac2b62e4:g:8z8AAOSwYoZduLlJhttps://www.ebay.co.uk/itm/15V-18V-24V-Dual-DC-Power-High-frequency-Square-Wave-Double-AC-Output-12V-DC-IN/172855736308?hash=item283f0137f4:g:1DEAAOSwGIBZsVa9

author: mansaxel
author_rank: Super Contributor
timestamp: August 19, 2020, 07:52:23 pm
content: It is very simple to roll your own. Assuming you don't need more than say 500mA; a pair of 7915/7815 regulators, a diode bridge and some capacitors is all it takes. I've built one as a father-son moment at the bench, on a piece of stripboard. Took all of one hour to do. You can, in a pinch, supply it from a single-ended 24VAC supply, but that is not going to be very well regulated under load. I run the unregulated 30VAC on a centre-tap 3-wire system to where I want DC and put a regulator close to the consumers, since I'm using the power for small opamp-based audio balancing boards.

author: magic
author_rank: Super Contributor
timestamp: August 19, 2020, 08:04:07 pm
content: Quote from: mansaxel on August 19, 2020, 07:52:23 pmIt can work, you just need to double the capacitance. Advantage of that scheme is you don't need to mess with mains wiring, just use an AC wall wart. Even 18V one would do for light loads and they are relatively common.

author: rstofer
author_rank: Super Contributor
timestamp: August 20, 2020, 03:25:00 am
content: Murata NCS6D1215C if 200 mA is sufficienthttps://www.digikey.com/products/en?keywords=murata%20NCS6D1215C9V to 36V DC in, +-15V DC outI have used one of these for an analog computer and it works well!

author: rstofer
author_rank: Super Contributor
timestamp: August 20, 2020, 03:32:00 am
content: Why would you ask about a power supply without stating the maximum required current?All we can do is guess and that never turns out well in an engineering discussion.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 20, 2020, 05:07:53 am
content: https://circuitdigest.com/electronic-circuits/12v-dual-power-supply-circuitask again if your transformer doesnt have center tap wire on the secondary...

author: GreyArea
author_rank: Contributor
timestamp: August 20, 2020, 08:20:47 am
content: QuoteAh crap, because I'm a noob - that's whyThe specs state 1A @ +/-15v I must assume that split across each rail, so 7.5W per. This seems to rule out some of those eBay modules. Although the DC-DC 20W looks promising.QuoteThat's the kind of thing I was looking at, but althogh I 've spent the last few days looking at supply design I couldn't find one that covered exactly what I needed. I'll probably go for the ebay module but I'm still considering putting one together myself. One of the questions I had was the choice of transformer as some documents seemed to suggest that a "special" winding could be added for a negative. Like I say, Ideally I'd like a reading resource if possible.Thanks for the replies.

author: mikerj
author_rank: Super Contributor
timestamp: August 20, 2020, 09:39:02 am
content: The other thing I can't see if what power source do you want to use? e.g. 240VAC, a DC voltage lower than 15V, a DC voltage higher than 15V?

author: magic
author_rank: Super Contributor
timestamp: August 20, 2020, 09:41:21 am
content: See the first schematic here for a generic mains-powered dual PSU with a center-tapped transformer. This might even do 1A assuming a sufficiently big transformer and enough heatsinking on the regulators.https://electronics.stackexchange.com/questions/266868/building-a-dual-rail-regulated-dc-power-supply-1-diode-bridge-center-tapped

author: rstofer
author_rank: Super Contributor
timestamp: August 20, 2020, 02:41:03 pm
content: Quote from: GreyArea on August 20, 2020, 08:20:47 amI would guess 15 Watts per output, total 30W. If 1A leaves the positive supply, wanders through the circuit and then returns through the negative supply then you have a change in voltage of 30V at 1A or 30W total. Even if the center point was used as a circuit ground the effect is the same. 1A leaes the +15V output and returns through ground - 15W. 1A leaves the center ground and returns to the -15V output - another 15W. Total 30W. I had the negative start at the ground point just to keep the signs consistent with current flowing + to -.It's fairly obvious in the center tap example that the grounded center tap has current coming in from the + supply and leaving from the - supply and if they are equal, the net current in the center tap is 0A. This leaves all of the current that leaves the + supply returning through the - supply and we're back to the original 30V example.