DIY USB-C, low noise, quad output ±12V power supply for oscilloscope probes - Page 1
Forum section: electronics / projects

author: nexus
author_rank: Regular Contributor
timestamp: September 06, 2025, 03:35:18 pm
content: Hi all,Recently wrapped up a project that came out nicely.This is a compact, low noise, quad ±12V power supply that is USB-C PD powered. It is meant to power universal current/differential probes as seen from Hioki which are also sold by Agilent/Keysight/Yokogawa with their own labels.The usual power supplies sold with these probes are big clunkers, and are also quite expensive, even used. While the price of this power supply (in 1-off qty) isn't that much cheaper (using fairly high-end parts), I believe the compact, lightweight nature of the new box makes it much handier.Schematics, gerbers, STEP files, BOMs are all on this page along with a full writeup:https://neonkev.com/2025/09/06/diy-usb-c-low-noise-quad-output-%c2%b112v-power-supply-for-oscilloscope-probes-keysight-agilent-yokogawa-hioki/Enjoy.I'm thinking to make a USB-C powered Tekprobe adapter next. I've seen some nice USB Type-B powered projects for Tekprobe; I can build on that while leveraging Type-C PD to improve size and performance even further.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 06, 2025, 05:00:07 pm
content: Nice work!One other point, it can also be used as a very-low-noise supply for testing other circuits, e.g. op-amp circuits that may require dual rails and so on, even if the voltage setting is hard-coded in resistors : ) The project is versatile, since it could be used to power all manner of circuits, sensors and so on.I'd be interested in a TekProbe adapter, but it's low-pri for me for currently. I tried to do a semi-similar thing, except I didn't use USB-C, just a 5.5mm DC barrel socket. Also, my implementation only supported power for potentially just one probe. Like you, I used the LT3045/94 chips too.However, I never got around to assembling into an adapter (the TekProbe end is a bit fiddly, I created a PCB to surround a BNC connector, but needs some construction thought and I believe I needed to re-think some parts of that from memory.In the end, I gave up (mainly because I only have one probe, and I don't use it often anyway - but I'd probably use it a bit more if I didn't need to pull out the Tek 'scope to use it).I've not done much testing, only looked at one of the positive rails, but it certainly appears lower-noise than a typical bench supply. Somewhere around 100-150uV RMS perhaps, with a well-selected DC power brick. A Meanwell brick was used for the screenshots, but with a Fairway one, the result was visibly worse. I can see you're using a decent brand USB-C PSU from the photo. (Also, good hint regarding the LEMO connectors : ) I needed one for an unrelated project and ebay was the only affordable option!In the attached photo, at the far right, is a hack to connect a probe (it's a 2.5 mm audio socket, that by chance is the right size to fit some R&S 'scope probes).Although I didn't complete this TekProbe supply, the PSU has occasionally been useful for other purposes.

author: voltsandjolts
author_rank: Unknown
timestamp: September 06, 2025, 05:05:11 pm
content: Quote from: shabaz on September 06, 2025, 05:00:07 pmThis might be of interest:https://www.eevblog.com/forum/circuit-studio/example-project-tektronix-tekprobe-adapterbreakout/

author: shabaz
author_rank: Frequent Contributor
timestamp: September 06, 2025, 05:38:27 pm
content: Quote from: voltsandjolts on September 06, 2025, 05:05:11 pmHi!That was actually very useful, that was my main reference from memory (it was a couple of years ago).The attached photo shows the only minor implementation difference was that I intended to have the PSU and Tekprobe BNC socket together in an enclosure, and not directly mounted on the 'scope, but via a BNC cable.To do that, I was going to fit the PSU into an alu enclosure, and then the green tekprobe board would have replaced the alu end panel on that enclosure.The pin header socket to the left of that would have plugged onto the PSU board outputs.The little black board was for the BNC socket in a few orientations but I think I either got that board wrong somewhere, or the holes didn't align on one of the boards - can't recall. The plan was that the SMA connector to the left would have been used to attach a panel BNC socket on the panel at the far end of the enclosure (where the DC barrel socket also is), so that one could use a BNC cable from there to attach to the 'scope. Anyway, it was all rev 0.1 stuff, and I made some mistakes along the way.

author: nexus
author_rank: Regular Contributor
timestamp: September 06, 2025, 07:04:11 pm
content: Quote from: shabaz on September 06, 2025, 05:00:07 pmAbsolutely; an adjustable output version wouldn't be difficult to implement. Since LT3045/94 just need one resistor to set voltage, pot of any variety could make voltage setting easy. Current limit is the same.Perhaps the same thing in an adjustable output version for general purpose use (banana jack, pin header. small coax output) similarly utilizing Type C PD would be handy.Since the LT3045/94 can be paralleled for increased current output, something like an adjustable low noise supply from 0-20V, 0-2/3A should be possible using 65W PD.However, to prevent excessive heat in the LT3045/94s at lower output voltage levels, a micro would probably be useful to negotiate PD voltage lower on-demand, so as to limit dropout at the regulators.I like this idea. Adjustable, compact, ultra low noise, general purpose Type-C powered supply.If differential voltage is required, maybe a split rail supply with independent adjustment or tracking between pos/neg outputs, depending on user setting.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 06, 2025, 07:44:07 pm
content: That feels like an awesome project, and nice reuse of much of the design you have.Incidentally, I just remembered that the quad-psu board has a LM317 and LM337 in the +-15V output paths, main reason was to drop some voltage, since the most common DC-DC converter I had was 24V output, and I didn't want to dissipate everything in the LT chips. Just mentioning this in case anyone was wondering what those TO-220 parts in the photo were for.The LM313/LM337 have reasonable PSRR below 100 kHz or so, but still a small amount of PSRR in the range to 1 MHz which may have helped in part too, but probably not much.By the way, just looked at the BoM, that Hirose connector for board connection is really neat, not seen that before.