Benchtop Power Supply question - Page 1
Forum section: electronics / beginners

author: BorisKontorovich
author_rank: Newbie
timestamp: August 05, 2017, 05:58:29 pm
content: Have a question, wondering if anyone can answer:I am looking at two bench top power supplies made by Keithley. Among different specs for these supplies, there is ripple and noise rating:2231A-30-3has the following spec:The RIPPLE AND NOISE Voltage:1mVrms/5mVp-pCurrent:6mArms2220-30-1has the following spec:The RIPPLE AND NOISE Voltage:1mVrms/3mVp-pCurrent:6mArms2231A-30-3 goes for about $600 and the 2220-30-1 is about $1200If you put all the other differences aside, does Vrms rating make a huge difference for general purpose use?Where would it become important?Any help is greatly appreciated. Thank you.

author: 2N3055
author_rank: Super Contributor
timestamp: August 05, 2017, 06:47:32 pm
content: Simple answer, most of the time no, it doesn't..It really depends what are you doing and what you expect from it. For general purpose work, Keysight, Tektronix,Keithley, Siglents and Rigols are overkill most of the time, and even simple cheap PSU will do.Many people have old linear PSU-s too.. If you only simply power circuits with it, many circuits are not very sensitive to power quality.On the other hand, some sensitive circuits are very picky about power. So picky, in fact, that you have to battery power them...So it really depends.If you think you will use it as a precision power supply, than again, that job is more adept tu SMU units...Also do you want to control it remotely via some program or script ? For that you need one with good connectivity.

author: medical-nerd
author_rank: Regular Contributor
timestamp: August 05, 2017, 07:25:49 pm
content: HiyaAs an aside - what ripple is normal / acceptable for a bog-standard benchtop power supply in the $200-300 price range?Cheers

author: alm
author_rank: Super Contributor
timestamp: August 05, 2017, 07:50:07 pm
content: Depends on the type of power supply. A good linear power supply with a fairly low current rating can easily go down to well under 1 mVp-p(some old HP supplies I have are something like 200 µVRMS). A switching power supply will usually be much higher, could easily be 10 mVRMS. Hybrid power supplies, as I suspect these are, are somewhere in between.I like low noise power supplies because I use a bench supply as a known good power supply when troubleshooting. The last thing I want is the power supply injecting noise in the circuit while troubleshooting a power supply noise issue. But you would likely be less worried about it if you were powering digital circuits that generate plenty of noise anyway.I would not be too worried about this fairly minor difference (no difference in RMS noise, only slightly higher peaks). If 5 mVp-pis not good enough, then likely neither is 3 mVp-p.

author: 2N3055
author_rank: Super Contributor
timestamp: August 05, 2017, 09:44:58 pm
content: Quote from: medical-nerd on August 05, 2017, 07:25:49 pmI agree with alm, better quiet than noisy.But, it really does depend what you're doing.. Some noncritical digital circuits might be fine with 50 mV of noise.. Some circuits have their own regulators so they will filter additionally..And you don't necessarily need fancy brand name 1000 USD PSU to get quiet solid unit. Some very cheap ones are ok too.Amongst others, I have two very inexpensive 30V/3A linear PSUs. They have no more than 1mV RMS noise, good regulation and are surprisingly stable... After 5 years, readouts are still accurate to the last digit....I use them all the time, when I don't need programmability and fancy features.. A friend of mine bought one and gave it to me to measure it to see how good it is. I liked it and went and bought two for less than 100$ each..But there are no assurances that if I go and buy another one it will be same inside, and that it will behave the same... That's the problem with the cheap stuff.With brand name units you get assurance that datasheet is correct, and that unit will be of reasonable quality even if you didn't verify all parameters yourself to be sure it is as they say..

author: tautech
author_rank: Super Contributor
timestamp: August 05, 2017, 10:11:57 pm
content: Quote from: 2N3055 on August 05, 2017, 09:44:58 pmThis ^^^To add that for most better PSU's the p-p ripple is rated at full output and that's something that's rarely used and when one does super low p-p ripple specs aren't normally of concern. At full output fan noise if the PSU has a fan is normally of greater concern.Power on overshoot is what many worry about too, you don't want the PSU to kill your circuits.