Noise level of Power Supply - Page 1
Forum section: electronics / beginners

author: hobbyee
author_rank: Newbie
timestamp: August 12, 2023, 03:35:23 pm
content: Hi forum,I am a hobbyist. Just bought a Korad KA-3005P power supply from Amazon. I noticed quite a bit of noise from the output. You can see them from the edges of oscilloscope lines. I am not sure if this is normal. It would be great if someone can provide some advice.Thanks!

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 12, 2023, 03:48:05 pm
content: Normally it's said to set the BW limit to 20MHz, or it will pick up all sort of stuff.Not to mention it's a breadboard, where every segment is a potential antenna.Specially with the ESP32 emitting RF! What happens when you connect it right to the PSU with a small load resistor?Also, you'd better join ground and earth (Green plug), in the way you're using it the scope is doing the earthing, not good!Sometimes at work I get into a new area where a wall socket is screwed up, appart from ocassional 200V "affection" when touching the chassis, the scope freaks out in all sort of ways.So I've learned (The hard way) to always start a in new workplace by measuring between myself and the chassis parts/earth socket before anything else!

author: hobbyee
author_rank: Newbie
timestamp: August 12, 2023, 05:41:49 pm
content: Thanks David. Really appreciate it.I connected negative to the ground and put 100 ohm resistor between + and -. The oscilloscope graph pretty much did not change. I do not have other power supply to compare. Should I expect it to be better?

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 12, 2023, 06:04:56 pm
content: Ah! Now you zoomed it became more obvious to be some sort switching noise...?Depending on the PSU quality this will vary a lot, but 1Vpp is a lotBut isn't it a linear PSU?Theschematicsshowed no switching topology.Maybe it needs new capacitors? Old ones might measure ok in capacitance, but ESR gets higher with age.I've replaced docens of caps in old Tektronix scopes, their capacitance was ok but ESR was 2-10Ohms.If you plan to replace them, check out the Panasonic EEU series, I measured 25mOhms in the 470uF caps I replaced.

author: veedub565
author_rank: Frequent Contributor
timestamp: August 12, 2023, 06:50:40 pm
content: I sometimes have to test PSU noise and ripple at work, it's usually a PITA. There's a method here that might be interesting (procedure page 15, setup page 12)https://www.keysight.com/gb/en/assets/9018-05624/service-manuals/9018-05624.pdf?success=trueSometimes you have to use fixed resistors to load the PSU because the electronic load adds noise to the line.Also use short, shielded wires and connect the shield to earth/chassis at one end.The shielding of the scope / RF Millivoltmeter also has an effect as it could be picking up crap. In the procedure I linked they use a LeCroy differential amp, and the shielding on it is rubbish it picks up all sorts of crap.I was testing a PSU at a customer site once and there was loads of noise, I couldn't understand it.. then the cleaning lady appeared around the corner with the floor polishing machine.. spewing out RFI all over the place. Was fine once she'd bogged off.Personally, I think outside of a lab environment it's very difficult to measure PARD on a PSU.**Edit**Looking at your picture, I would disconnect the circuit you have attached, and try it with a simple resistor across the output of the PSU to load it, the circuit could be adding ripple on the line.And yes set the bandwidth limit, 20MHz for the Keysight PSU's but even then you sometimes picking up crap unrelated to the PSU.

author: Bud
author_rank: Super Contributor
timestamp: August 12, 2023, 06:59:13 pm
content: Turn on Bandwidth Limit on the scope as the other user said. You have it off in the photo.Experiment with turning off equipment and LED/Fluorescent lights in the room. The scope may be picking up noise from your computer or router power supply, etc.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 12, 2023, 08:02:45 pm
content: Quote from: Bud on August 12, 2023, 06:59:13 pmIndeed. You have a quite nice scope, but still lack some experience. It is simply unrealistic to do a measurement over a 100MHz bandwidth with the long ground lead and crocodile clip you have on your probe.Try this: Hold that GND wire in your hand, move it around and twist it. Very likely you will see the measured noise shape change on your oscilloscope. At that bandwith the GND loop is partially acting as an LC oscillator and to do proper measurement with such a bandwith using the small short spring clip GND is mandatory. The long lead with crocodile clip is convenient, but only usable for measurements with a lower bandwidth. And limiting the bandwidth to 20MHz while using the long crocodile clip is a more fitting combination.And besides that. Korad KA-3005P is a budget power supply. It's already quite amazing it can deliver that output power for that price. You can't expect much for noise, precision and accuracy. But still, for the price it's still a pretty good power supply.

author: Eraldo
author_rank: Regular Contributor
timestamp: August 12, 2023, 09:10:23 pm
content: According to the manual of the psu it has a 2 mv rms noise so about 12mV P-P so that's unusual. Also by the size of the psu and the noise specs it should be a linear psu so there shouldn't be any switching noise. Most likely external noise.Attaching a load to it would improve things and give you a more accurate reading. Add a resistive load as others said and try to make a direct connection using the osc probes. Attach the resistor through the poles using the screwing mechanism and just connect the probe across the resistor legs. Also turn off all possible switching devices in the vicinity and don't put any other load during measurement. Try it with different current values too (using power resistors)And do share the results when you do

author: hobbyee
author_rank: Newbie
timestamp: August 13, 2023, 02:14:17 am
content: Thank you all! I learned a lot today from you.Here are a couple more test I did. I set BW Limit to be 20M. I also directly screw the resistor on the power poles. I tried 100 ohm and 1.2k ohm. Basically, the noises remains as is.As a comparison, my ESP32 project can also be powered by a 18650 battery or a USB from my computer, where I cannot see those noises. So, I am not feel like they were introduced by the probes or environment.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 13, 2023, 09:47:33 am
content: For testing the supply noise one should use a more passive load, like a resistor, not an RF or µC project that causes switching artifacts.Testing with a variable load is a different thing and needs care with the probes / ground. The supply may not provide good higher frequency decoupling. If needed there should be suitable capacitors on the board that is powered from the supply.

author: Andreas
author_rank: Super Contributor
timestamp: August 13, 2023, 10:12:38 am
content: Hello,I usually use those connectors and BNC cables to reduce the stray from environment to the measurement.https://www.digikey.de/de/products/detail/cal-test-electronics/CT2939/6005472On my KA3005P i get this picture with 20 MHz BW limitBut I am shure that the spikes all 19 ms are not from the power supply but something else (maybe USB-Cables near the setup).with best regardsAndreas

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 13, 2023, 10:44:04 am
content: 20ms = 50Hz mains interference, perhabs the PFC from the computer PSU or something else.Yeah try disconnecting everything close to it.My computer caused a lot of HF noise until I found a doggy earth connection in the wall socket.Try zooming on one of these spikes!I don't think the PSU is noisy at all, try measuring other power sources, if you find the same pattern... You know it's not the PSU.

author: iMo
author_rank: Super Contributor
timestamp: August 13, 2023, 11:20:34 am
content: I've been just repairing and testing a cheapo linear psu called Mastech Hy1503D (LCD displays). I added ceramic blocking 100n ceramic capacitors on many places (at the diode bridges outputs, at the opamps power pins, 78xx outputs, etc) as I was lacking them there. With 15V loaded with 1A (15ohm resistor) I do not see any output noise (measured at the resistor) with my analog scope set to 5MHz BW and AC 5mV/div.

author: radiolistener
author_rank: Super Contributor
timestamp: August 13, 2023, 06:42:36 pm
content: this is noise of your environment and wires... KORAD KA3005 also has some noise from dynamic LED indication, but it is much smaller.It looks that you're using WiFi module close to your circuit, WiFi transmitter is very powerful (about 1 Watt at 2.4/5 GHz) and can easily induce voltage spikes on your low frequency circuit placed at about 0.5-1 meter distance. Try to shutdown all WiFi and BT routers and modules in your room and check if it helps.I also had issue with low frequency voltage spikes from DC to about 100-200 kHz due to WiFi router working at 1 meter distance from circuit with operational amplifier. The main power of these spikes is within bandwidth from DC to about 10 kHz, but still well noticeable up to 200-400 kHz. The frequency of these spikes depends on WiFi activity, when there is no activity it happens about once per second. When I power-off my WiFi router, all DC spikes are gone...

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 13, 2023, 11:12:55 pm
content: All sorts of things can generate noise that can get picked up by your scope. Your PC, monitor, keyboard or mouse, lighting, your soldering iron. One way to go hunting for the noise source is to turn your equipment off one at a time until the the noise disappears. And then you can decide to either fix it permanently, or just live with the noise and maybe turn that piece of equipment off when you have some sensitive measurement.

author: hobbyee
author_rank: Newbie
timestamp: August 23, 2023, 07:10:29 am
content: Today, I received the GWInstek GPP-4323. As a comparison, I did the similar test by putting the same resistor between + and -. GPP-4323 looks a lot cleaner. Please see the photo.Korad disappoints me even more on the other stuff. You can do some search and find their Chinese website. Basically there is no customer support, nobody returns to me email, there is no warranty although they claimed 1 year warranty. I wish I did not buy their stuff.

author: Andreas
author_rank: Super Contributor
timestamp: August 23, 2023, 07:47:59 am
content: Quote from: hobbyee on August 23, 2023, 07:10:29 amHello,As stated above the "noise" is not from the power supply.So I would recommend to repeat the test on both devices one after the other.The devices side by side.And powered from the same outlet (if in doubt).Without switching any LED-Lamps or other EMI producing devices between the tests.with best regardsAndreas

author: hobbyee
author_rank: Newbie
timestamp: August 23, 2023, 07:58:33 am
content: Yes, that’s exactly what I did. It was one after another. I did not post Koard graph because it is same as the one I posted earlier.The point I am trying to make is korad has more noise than GPP-4323.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: August 23, 2023, 09:45:55 am
content: I have a Korad KA-3003P PSU (Tenma branded version), so essentially same as 3005, just lower-spec 3A version, and I don't get any such noise on the output.Tested just now in same way - 100 ohm load resistor across the output terminals, 3.3V output, o'scope probe attached to the leads of the resistor. I just get a general broadband fuzz of 20 mV pk-pk noise, and no spikes or anything. This is with scope/probe in 10X mode, 20 MHz bandwidth limit on, AC coupling.I am pretty sure the noise you're seeing is from the environment.Have you tried using the coil spring ground clip on your probe? Siglent probes should be supplied with one. It shortens the ground loop and avoids the ground lead acting as an antenna and picking up ambient noise. Place the tip of the probe on one side of the resistor, and the ground spring on the other side.Edit:Attached is a 'scope screenshot when probing my PSU with coil spring ground. Approx 5 mV pk-pk noise. This is with the 'scope, my PC, and wi-fi router powered on in the room.

author: radiolistener
author_rank: Super Contributor
timestamp: August 23, 2023, 12:06:43 pm
content: you can check if noise source is PSU with power off PSU, if noise disappears, it was produced by PSU

author: hobbyee
author_rank: Newbie
timestamp: August 23, 2023, 03:09:50 pm
content: Thanks for all the replies.Can someone directly answer this question? As I am doing side by side comparison, under exactly same condition, regardless "ultimate" source of noise or oscilloscope coil or anything, one power supply showed more noise, another one showed less, does that mean the one showed less is better? Should I expect the Korad produce the same result?I understand I can keep looking for the source of issue or I can add some capacitors to fix it. My point is why Korad cannot produce the same result as Instek. Because it is cheap or because it is bad or defective?

author: jonpaul
author_rank: Super Contributor
timestamp: August 23, 2023, 03:16:39 pm
content: Get full specs and schemat of each PSU.Test under resistive load, no load, etc.Use NO probes, just a direct BNC><cable to PSU terminals, AC couple scopte.See the fine HP Power Supply Handbook for measurement of PSU PARD (periodic and random deviation)Jon

author: Andreas
author_rank: Super Contributor
timestamp: August 23, 2023, 03:17:33 pm
content: Hmm,not shure: but is there a connection between green (Earth) and black (Ground) socket on the Korad?In this case you have a ground loop since the oscilloscope has also connected the ground pin to earth.with best regardsAndreas

author: hobbyee
author_rank: Newbie
timestamp: August 23, 2023, 03:21:37 pm
content: Yeah, you have good eyes. I did it because it was suggested earlier in this thread but that connection did not change anything (I have earlier photos showed it).

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 23, 2023, 03:55:31 pm
content: As a sanity check, to rule out weird ground loops via EMI caps between line voltage and chassis, connect both the probe tip and ground clip to the power supply's negative output:

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 23, 2023, 04:30:25 pm
content: Chinese price means Chinese customer service.Don’t get me wrong. Most times Chinese products will deliver an excellent performance commensurate with the price. But if something goes wrong, you are usually on your own.

author: radiolistener
author_rank: Super Contributor
timestamp: August 23, 2023, 09:26:36 pm
content: Quote from: hobbyee on August 23, 2023, 03:09:50 pmit is unclear what is the source. Most of all the source is your measurement wires which receive RFI noise from environment. Because your setup looks very weak for noise RFI. For example, ground clip of oscilloscope probe is a good antenna for such noise. Also received noise depends on PSU output impedance and many other things that needs to be taken into account.Try to not connect probe to PSU output but place it's ground clip shortened on probe pin at the same position near PSU, does it receive noise? Then try to touch PSU ground with ground clip shortened on probe pin. Does noise appears?

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2023, 09:28:29 am
content: Quote from: Kim Christensen on August 23, 2023, 03:55:31 pm^^^ This ^^^Or use a differential probe but do this test first.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 24, 2023, 11:42:57 am
content: Additionally, I'm quite certain you see a lot less noise if you buy a EUR1500 power supply and view it's output with an EUR80 oscilloscope

author: pdenisowski
author_rank: Super Contributor
timestamp: August 24, 2023, 03:09:58 pm
content: Quote from: veedub565 on August 12, 2023, 06:50:40 pmQuote from: Kleinstein on August 13, 2023, 09:47:33 amYes and yes. I'm actually working on a presentation on this very topic right now and could not agree with both of you more.

author: pdenisowski
author_rank: Super Contributor
timestamp: August 24, 2023, 03:10:47 pm
content: Quote from: Doctorandus_P on August 24, 2023, 11:42:57 am

author: PinheadBE
author_rank: Regular Contributor
timestamp: August 24, 2023, 10:08:56 pm
content: Still on topic, but with a different supply.I have a (switching) PS from Meanwell laying around that I would like to put to good use. It's a RS-150-5 capable of delivering 26 A under 5 V.Of course, I will rarely use it at full power; more likely in the range 1 - 3 A. But since I have it and do not use it for anything else....https://www.meanwell.com/productPdf.aspx?i=419#1The specs states 80 mV p-p (max) Ripple and noise.Is there a way I could filtering a significant part of that, to be under the 10 mV p-p or even less ?I know I could add a big fat cap on the output, but:- what about the peak current when turning on ?- What about the cap discharge when powering off ? In this case, adding a diode will add a voltage drop that could not be compensated by 0.5 V overhead the PSU can supply (the ouptut is adjustable from 4.5 to 5.5 V)Any suggestions ?

author: Electro Fan
author_rank: Super Contributor
timestamp: August 25, 2023, 01:44:20 am
content: might be something useful in here…probe connections - both tip and ground clip - definitely can impact the resultshttps://www.eevblog.com/forum/testgear/korad-kd3005d-bench-supply-power-on-spike/msg3509594/#msg3509594https://www.eevblog.com/forum/testgear/rigol-scope-probe-to-bnc-adapter/msg672014/#msg672014https://youtu.be/zodpCuxwn_o?si=WB1it9-i5zzl0BCV