Looking for a quiet bench powersupply - Page 1
Forum section: electronics / testgear

author: olepr01@gmail.com
author_rank: Contributor
timestamp: December 20, 2014, 06:48:29 pm
content: HelloI'm currently doing some phase noise and stability experiments on OCXO's, and powersupply noise is a factor. Also, stability measurements of OCXO's and GPSDO's can run for weeks or months, and I am not completely sure I trust my current bench powersupplies, mainly eBay surplus gear, to remain switched on "unsupervised" for that long.So I'm considering purchasing a brand new bench powersupply. The biggest reason is of course the fire hazard, but I would assume any bench powersupply from a reputable manufacturer would be suitable.I'm thinking 2 or 3 outputs, up to 30v or thereabouts, 2-3Amps per channel - nothing special.Next on the list is noise. I suspect theres a lot of "unstated" information in a spec-sheet, so I am not at all confident that I am interpreting the datasheets correctly. But so far I've narrowed it down to two Hameg units:HM7042-5 - Ripple ?100µVrms (3Hz…300kHz), current ripple not statedHMP2030 - Ripple <150µVrms (3Hz…100kHz), <1mArmsAs the specs are not directly comparable (different bandwidth, current ripple not stated), I am a litte unsure about which of these are better for my intended use; to power sensitive low noise measurement circuits. Also, are there other, even lower noise supplies out there in the same pricerange?Any advice is greatly appreciated!

author: robrenz
author_rank: Super Contributor
timestamp: December 20, 2014, 08:02:02 pm
content: HP 6114AHP 6115APower Designs Precision 2005, 2010, 2020 etc.You will not find quieter or more stable supplies than these oldies until you spend well past $3000.00 today.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 20, 2014, 08:33:46 pm
content: I recently went through this exercise and discovered the old HP/Agilent 66xx series to be rather fantastic. You can get 3 of them for a lot less money than a new 3 channel mid-range unit AND get better performance. Generally way better than 100uV of ripple and you get remote sense - most 3 channel supplies will not have that either.I was prepared to pay big bucks for new supplies until I tried these - pair of 6653a 0-35v/15A. I am now looking for a lower voltage/current version for finer control.

author: nixfu
author_rank: Unknown
timestamp: December 21, 2014, 05:13:31 am
content: As a amateur radio operator who worries about any RFI at all from my gear that I have on the bench in the same room as my radio shack.I suggest getting a surplus HP programmable power supply. I have a HP 6632A on my bench, and I have noticed it is very very RFI quiet. You can find a very good quality HP used for $250-400 on ebay depending on your voltage/amp requirements etc. I am not sure you can find a better deal as a hobbyist than a good used HP 6xxxA power supply since the market is flooded with them from labs, govt, etc.Also as a general rule, a linear power supply is going to be much more quiet than a switched mode power supply. I avoid switched power supplies as much as possible.You can also use some ferrites, and add some common mode suppression on power and signal lines to reduce any RFI even further.

author: tautech
author_rank: Super Contributor
timestamp: December 21, 2014, 06:24:22 am
content: You also need be aware some modern PSU's ripple spec's are only accurate when averageing is used to measure the ripple.Try a P-P measurement and no way can you acheive manufacturers advertised specs.Be warned.

author: asteroidz
author_rank: Newbie
timestamp: December 21, 2014, 08:28:09 am
content: Agilent E3631A seems pretty good.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 21, 2014, 08:37:11 am
content: you need to be very cautious about the WAY noise is specified/characterized. RMS, p-p, weighting, gain structure etc.....what bandwidth is the noise rated over.....on paper you can make anything look good (with enough fine print)...what matters is stability and accuracy over a realistic, real world situation.....I.E. load and line regulation vs temp....transistor junction stability/time....it's very easy for me to take a less than stable power supply and make it look fantastic on paper....another consideration, is how does the supply isolate mains from DC output.....are there dramatic changes over a long term trend....how does the load regulation interact with freq vs impedance (capacitive loads etc).....slew rate....this could go on and on, but the point is don't be lulled into a false sense of security, on the basis of "specs"...in the used market, some things age well (get better) some don't (fail).....

author: robrenz
author_rank: Super Contributor
timestamp: December 21, 2014, 04:21:58 pm
content: IMO the Power Designs and HP 611XA units get better with age.Here is a post of ripple measuermenton a old 2005A supply

author: Vgkid
author_rank: Super Contributor
timestamp: December 22, 2014, 01:25:35 am
content: If your designing this for use, then use whatever power supply you will use for the project. a basic linear power supply is rather useful. Look into the linear power supplies from Condor/Power one/ Ac/Dc electroncs / Sola. or make your own. no need to run with ultra stable power supplies. Most high performance crystal oscillators are specced as having an PSU error of either 5%(some older models) or 10%.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 22, 2014, 02:14:12 am
content: Quote from: Vgkid on December 22, 2014, 01:25:35 amhonestly, every-time I need a "precision" PSU I just build up my own DC-DC converter. You can virtually eliminate the unknowns in the DC source that way. Also I am then relying on my own "specs" rather than some theoretical ideal in a datasheet.As long as the DC source you are using (input to DC-DC) can drive large capacitive loads, then you can just load it's output with the necessary filters. That way you can characterize and control your test.Of course the other option is to just trend the output discrepancies of your DC supply, and then subtract/factor those into your data, from the DUT.....