Compact 9v supply and ground loops - Page 1
Forum section: electronics / projects

author: dilbert
author_rank: Contributor
timestamp: April 09, 2013, 09:50:01 am
content: Hello, i'm designing a compact 9V power supply for musicians. I wanted to check a couple of things with you before it goes "smoke" on the water.It should accept AC voltages from all over the world and output a few(4-8) 9V 250mA DC channels.My basic idea is:1.input fuses and little filtering2.90-264V to 12V switching transformer3.big 12v 105°C cap4.one or more linear regulators to 9V5.final small 9V caps per channel(ok the hybrid regulating thing has already been done,but i didn't knew it!See?I have a couple of good neurons, if you teach me)A thing to keep in mind is that many instruments/pedals are very poorly designed(even for my knowledge) so you must expect them to have a poor to non-existent power supply section, expect ground loops and noise pickup even from Saturn rings' static.From experience, a pedal A can interfere with pedal B attached to the same supply line, and vice versa.My first tought was to use a single linear regulator per channel, but they consume a lot of space,money and heat.Would a single 9V linear regulator followed by an LC filter per channel do the job? We're not interested in high frequency noise, mainly in mains hum and audible frequencies.Heavy discounts for anyone who helps

author: hlavac
author_rank: Frequent Contributor
timestamp: April 09, 2013, 01:36:25 pm
content: Quote from: dilbert on April 09, 2013, 09:50:01 amTotal heat will be almost the same if you use multiple regulators, just spread out over multiple devices. 7809 with a small cap on output may be even cheaper than LC filter per channel!You will need pretty big choke for AC line frequencies...

author: olsenn
author_rank: Frequent Contributor
timestamp: April 09, 2013, 01:41:21 pm
content: QuoteI've got the perfect solution!

author: Psi
author_rank: Super Contributor
timestamp: April 09, 2013, 01:46:22 pm
content: You could include a few small isolated DC-DC modules if needed.

author: hlavac
author_rank: Frequent Contributor
timestamp: April 09, 2013, 01:59:07 pm
content: As for the ground loops, that will be a real pain. Because all the signal cables connect the grounds, you would be better off totally isolating (floating) all the power supply channels. But that is a completely different league in terms of cost and complexity and there goes your "compact" as well...Cheapest isolated DCDC 9V modules I have found in a quick look arethese. So you could use an universal 5V switching adapter to power 4+ of these (one per channel), with some extra filtering on the outputs.Or you could do even better and use 12V DCDC modules and still use one 9V linear regulator per channel to cut down on the switching noise. Probably the best way.

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2013, 04:27:19 pm
content: Simplest will be either a multiple secondary transformer ( you can DIY from a kit if they are still available as they come with a prewound primary) and do a simple bridge, cap and regulator for each output, or just get a big 9VAC unit, a bridge and a capacitor and then a whole lot of the isolated modules.

author: hlavac
author_rank: Frequent Contributor
timestamp: April 09, 2013, 04:56:04 pm
content: Transformer would be problematic, ouput voltages would vary with different AC mains voltages, he wanted to be universal...Also 9V/0.25A is more than 2W, you would need bigger DCDC modules than those I have suggested (they seem to be only 1W)

author: dilbert
author_rank: Contributor
timestamp: April 09, 2013, 06:18:48 pm
content: Quote from: olsenn on April 09, 2013, 01:41:21 pmAfter some experience with them on field instruments and with musicians friends..they are tiny little gremlins,especially the rechargeable ones.Thanks anyway

author: hlavac
author_rank: Frequent Contributor
timestamp: April 09, 2013, 07:22:24 pm
content: So get a 3W whatever-to-12V DC/DC modules likeone of these, and stick a L7809CV after it and you should be fine...

author: dilbert
author_rank: Contributor
timestamp: April 09, 2013, 07:45:16 pm
content: Quote from: hlavac on April 09, 2013, 01:59:07 pmThanks a lot hlavac!

author: dilbert
author_rank: Contributor
timestamp: April 09, 2013, 07:50:38 pm
content: Quote from: hlavac on April 09, 2013, 07:22:24 pmthat's cheap