Single Shared or Multiple Power Regulators  - Page 1
Forum section: electronics / beginners

author: AndrewNorman
author_rank: Contributor
timestamp: November 05, 2021, 04:32:06 am
content: I am starting to work on a project where I have an interesting choice for the power distribution part.There will be around 1m from the first to the last module, so the power bus will be at least that long. The wiring harness will be used to pass 5V signals between the various modules, I expect that this will be at most 75cm in length. Each module will be using between 100-500ma, with around 10 modules in total.Should I have:* One 12V to 5V regulator, then a shared power bus for each of the modules.* A 12V power bus and local 5V regulator on each module.My current ideas/concerns:Shared ApproachThe 5V line would suffer from voltage drop across the length and end up below 5V at the end of the power bus.Bigger regulator to handle the bigger current load - might need more coolingLocal RegulatorsEach module would get aclean5V supply.Can size each modules regulator to match the modules need - maybe end up with a cheap overall total (not sure on this one yet)Not sure how the ground loops might get involved on this one, given I am not expecting the signal to change that quickly (at most 100hz) I think it should work ok. Same with signal quality with the long lines, hopefully shouldn't be too much stray capacitance screwing up the edges.Any suggestions, comments or general "you have got to be kidding"?CheersAndrew

author: Peabody
author_rank: Super Contributor
timestamp: November 05, 2021, 02:55:14 pm
content: Do you have a feel for the maximum aggregate current the modules would need? Is it 5A, or something significantly smaller? If one module's power dropped out, would you want the others to continue to run, or would you want to shut everything down?I assume you would be looking at switch-mode buck converters in all cases, not linear regulators. So that would be a controller, inductor, mosfet, diode and capacitor for each module. It's hard to see how that would be less expensive than doing all that once.I don't really know if the distances involved would make any difference as far as the power rails are concerned. Well, I'll defer to those who actually know about that.I don't have a recommendation for you. These are just some things that occurred to me that you might consider. If you had a 6V primary supply, you could use individual 5V LDO linear regulators at each module, which would be a regulator and two capacitors, all of which could be surface mount, and it would probably be less noisy.

author: Terry Bites
author_rank: Super Contributor
timestamp: November 05, 2021, 03:28:33 pm
content: If using a switcher: Use a single one to power the bus and some OV and OC protection per module- a fuse (or polyfuse) and a Zener say. How fussy are your modules?If linear: I'd go for a per module approach especialy if its a one off. One single regulator fail day and all your modules will suffer equal pain. A 1A regulator gives you plenty of headroom per module. A fat boy will cost you more I expect. The bigger they are the harder they fall. You could brew your own but it wont have all the protecion features of an intergated solution. OC and OC is a good idea what ever you decide.

author: Benta
author_rank: Super Contributor
timestamp: November 05, 2021, 05:59:30 pm
content: The distributed approach is the best from a technical, though not from cost.It's very usual to do this, the common term is POL for "point-of-load" regulators.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 05, 2021, 06:43:34 pm
content: A big part of the equation of whether to use a single big or multiple small power supplies is the allowable voltage drop.If you put the power supply in the center (instead of in a corner) then the length of copper track is halved, but also the amount of current though that track is halved, which results in a quarter of the droop at the "far" end of the PCB.

author: mariush
author_rank: Super Contributor
timestamp: November 05, 2021, 07:05:39 pm
content: To keep costs down, I'd consider having one or a couple 12v -> 5.5v..6v dc-dc converters and then use a cheap low voltage drop 5.5v-6v -> 5v on each module to smooth out the voltage.To put a 12->5v linear regulator on each module would be too much losses and too much heat if the module consumes 500mA (7v drop at 0.5A is 3.5w wasted)To put a 12v-5v switching regulator on each module (extra capacitors, diodes, inductors) would make this costly.75cm is not that big of a distance and you wouldn't have that much voltage drop at 500maSo you could have a 1a fuse on each module, a 500-700mA ldo fixed 5v output on each module, which can use just a couple ceramic capacitors that are cheap...You could have a 12v -> 5v 3A for 5 modules , so two such regulators for each group of 5. Or maybe a single 12v-5v 5-6A switching regulator.You could reduce voltage drop to the modules by using multiple wires, ex 2 pairs of awg24..awg20 or something like that.Fixed 5v regulators start from around 20 cents in volume on Digikey :https://www.digikey.com/short/rfbcf82vCan get 300-500mA regulators with less than 0.35v drop at maximum current.Adjustable regulators can be even cheaper, but you'll add 2 feedback resistors :https://www.digikey.com/short/c9qd18trAs for 12v - 5v switching regulators here's a list with some filters and sorted by quantity available in stock :https://www.digikey.com/short/71j8pcnrSee for example AP64500SP for a 5A regulator :https://www.digikey.com/en/products/detail/diodes-incorporated/AP64500SP-13/10419714For 3A -ish there's plenty, starting from around 50 cents ... but often is worth getting something that costs a few pennies more but you'll save by not needing a diode or compensation resistors and capacitors ..

author: AndrewNorman
author_rank: Contributor
timestamp: November 09, 2021, 05:28:05 am
content: Thanks guys, that is why I like this forum. Lots of good ideas/questions to think about.I am currently looking at going to go for a quality 12 -> 6v DC-DC converter at the top of the power bus. Then each module will have a LDO regulator and just connect to the bus as needed.Once I get something up and working I will post updates/pictures.

author: David Hess
author_rank: Super Contributor
timestamp: November 09, 2021, 01:42:35 pm
content: What happens when power is applied or removed and some regulators start up or shut down before the others, so some parts of the circuit are powered and others are not?Designs with multiple regulators may use tracking regulators to prevent this problem, but it adds a level of complexity. 10 modules over a distance of 1 meter with 5 total amps of current draw at 5 volts does not strike me as requiring anything more complex then heavier wire and connectors for power distribution.

author: Terry Bites
author_rank: Super Contributor
timestamp: November 09, 2021, 02:41:12 pm
content: I've built muticard sytems with per card regulation. I've never known some to start and others not- occasionally die maybe yes.I've seen power plant instrumentation card cages with hundreds of locally regulated pcbs.You can put out power good data from each module over your RS422. Add a low cost supervisor eg a MIC803-46 to flag the uC.Remote card reset and shut down.The central system should monitor the bus current and voltage for any anomalies.