Build my own 5v PSU or buy a precision lab psu? - Page 1
Forum section: electronics / beginners

author: mcstomach
author_rank: Newbie
timestamp: June 08, 2022, 07:46:14 pm
content: Hi,Im in need of a 5vdc power supply, with very low levels of ripple and noise.I was looking at buying the rigol DP832 psu for this, and future projects.I am aiming at a the low end of a few uV Vpp ripple at 5vdc, 200mA load.By looking at the internet - it seems plausible that I can make my own linear psu with that ripple characteristic. Or even better, maybe some of you have experience with evaluation boards with really low ripple output?For this particular project I dont really need an adjustable output.. So thats why Im questioning if its more reasonable to make my own psu..Any feedback is much appreciated!

author: nightfire
author_rank: Frequent Contributor
timestamp: June 08, 2022, 08:55:57 pm
content: Question: What is the application?I myself was thinking about the idea to use for some measuring circuits I wanted to build some rechargeable batteries I have around, and maybe drop some voltage by simple resistors or a linear regulator/mosfet.Of course, this would only work if operation of the powered devices are within the lifespan of the battery, and the voltage has maybe not to be precise 5VDC.Especially with some lead batteries and low power circuits there can be quite some time they hold up...

author: Benta
author_rank: Super Contributor
timestamp: June 08, 2022, 10:10:39 pm
content: An environment-friendly idea:Make a small board wtih two USB-C receptacles and build your regulator using the voltage regulator of choice on it.For input, use two series-connected USB-C mobile phone chargers, this will give you 10 V DC input. Enough for any linear regulator. And 200 mA is no problem at all.The chargers you'll find in any garbage dump or any drawer of a family member, or at home.

author: Benta
author_rank: Super Contributor
timestamp: June 08, 2022, 11:15:50 pm
content: Yes, all well and good.But all of the cheap USB-C 'phone chargers I've seen do not support all this. They only supply +5 V. Just read the label.

author: Bud
author_rank: Super Contributor
timestamp: June 08, 2022, 11:51:02 pm
content: With switching power supplies like those phone charges you are talking about several Tens of mV ripple at best, not several mV, let alone several uV.

author: bdunham7
author_rank: Super Contributor
timestamp: June 09, 2022, 04:07:14 am
content: Quote from: mcstomach on June 08, 2022, 07:46:14 pmSingle digit µVp-pis pretty challenging because that level of noise can show up from anywhere. An off-the-shelf PSU is not likely to come anywhere close to this. Something like the LT1965 can probably get you within an order of magnitude of that, which is pretty good, then perhaps you can add some shielding and filtering. Also, you need to consider the load--is it completely constant? If not, then load variations are going to be reflected on the supply voltage and then you need to consider the source impedance and line regulation. Passive filtering after the regulator will make this aspect worse.What are you powering?

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2022, 12:38:02 am
content: Microvolts of ripple requires a low noise reference and operational amplifier. Below is an example of the sort of circuit that is required. Last time I used it, it was with an LM329 buried zener reference and LT1007 low noise operational amplifier, which will require some external frequency compensation. In retrospect an LT1001 or OP-07 class operational amplifier would be as good or better for stability and noise. I used a PNP in place of the JFET and junk 7805 for a 10 volt output. The noise of the regulator is removed by the operational amplifier's feedback loop so only the noise from the reference and operational amplifier needs to be considered.

author: james_s
author_rank: Super Contributor
timestamp: June 10, 2022, 03:48:36 am
content: USB-C chargers are probably one of the last places I'd look, but then I don't have any of them or anything that uses one except for my work laptop. A much easier and less clunky solution than wiring two chargers in series that use expensive cables is to just find an old linear wall wart, the kind with an iron transformer in it. Most of those have a standard 2.1mm barrel plug on the end and it's very easy to find them in the range of 6-12V from a single adapter.

author: wizard69
author_rank: Super Contributor
timestamp: June 10, 2022, 09:04:00 pm
content: Quote from: mcstomach on June 08, 2022, 07:46:14 pmHiQuoteIf you have a very specific need buy or build a supply to satisfy that need. there are numerous analog power supplies out there used in the instrumentation world with low ripple, so buying is likely an option. Building a DIY solution is also a possibility. An example power supply that MIGHT meet your needs:https://www.osaelectronics.com/product/ulps1225b/While DIY is possible, I don't expect it to be easy to get to those low levels of ripple.QuoteDoes it have to be line powered? This is off the cuff but it likely would be easier to do a battery powered system with a low noise linear regulator for a DIY solution. If line powered is required I'd look up all the info possible for linear regulators with this sort of performance. That includes tech notes and articles in trades.QuoteAs you may have noted, power supplies that can actually reach the low ripple levels you desire are not cheap, especially from manufactures that can deliver!! The feasibility of DIY such a low ripple supply depends upon your engineering skills and time available.Quotemore detail might help the engineering inclined here. Also is there anyway to move to larger ripple values? In other words is the tight spec needed. Single digit micro volt level ripple is pretty aggressive in anything low end.As for a lab supply those are great to have but I doubt are needed here or even desirable. The Rigol DP832 may or may not be a nice lab supply (I don't have one) however it isn't even close to the ripple spec you are seeking. If you have considered the Rigol then I have to wonder where the tight ripple spec came from. Plus if microvolt level noise is a concern I'd be reluctant to put anything with digital electronics near by, even a step down transformer might be a problem.

author: tepalia02
author_rank: Regular Contributor
timestamp: June 14, 2022, 11:45:09 am
content: I would suggest that you buy a ready-made one and also try to build another by your own. If you have a ready-made one, making your own design and troubleshooting will also be easier.