Cheap bench power supply ripple and micro controllers - Page 1
Forum section: electronics / beginners

author: Kits
author_rank: Newbie
timestamp: December 16, 2023, 07:30:27 pm
content: Hi All,I got a new bench power supply off amazon, this one:https://www.amazon.co.uk/dp/B08TZVZQR6?psc=1&ref=ppx_yo2ov_dt_b_product_detailsI discovered after hooking it up to my oscilloscope that it has a much dirtier output than my older bench power supply (minleaf NPS605W).I mostly play with microcontrollers like esp32, esp8266, attiny85, etc and i'm concerned that the ripple on this supply is gonna damage them.I measured both with my oscilloscope using eev blog #594 as a guide and attached both waves running 12v at around 0.8 amps using a strip of LEDs as my load.my old minleaf got 38mv rms and 190 mv P-Pthe new supply got 558mv rms and 5.32 v P-P (not mv, Volts)I'm learning towards returning the new one as it stands but are these numbers as bad as I think they are and would it be dangerous to try and use it to power micro controllers.

author: 5U4GB
author_rank: Super Contributor
timestamp: December 17, 2023, 02:01:12 pm
content: Quote from: Kits on December 16, 2023, 07:30:27 pmJust a thought, could that be radiating or coupling noise back into your scope probes, see e.g.this post? One of the things that's recommended when taking noise measurements is to turn off LED lighting to avoid this problem (where the problem is usually the crappy driver, but see the linked post for other possible problems), you may have inadvertently chosen the worst combination of supply + load possible for making a noise measurement. What happens when you take the reading with just an appropriately-rated resistor as the load, and with other possible noise sources disabled? The figures you show are so bad I'd look for other issues that could be creating them... either that or you've got a spectacularly bad power supply.

author: Grandchuck
author_rank: Super Contributor
timestamp: December 17, 2023, 05:34:52 pm
content: It seems that the new supply is very noisy. Are you driving the LEDs directly or is there an intervening controller that could generate noise? You can try resistive loads if you have suitable ones.Perhaps there is a missing or defective filter capacitor in the new supply? That is a lot of noise!

author: RoGeorge
author_rank: Super Contributor
timestamp: December 17, 2023, 06:00:32 pm
content: How did you connect the oscilloscope? Attach a picture with the connected probes/wires.If your probing is correct, then your new power supply is unusable. It's either defective or bad by design.Return it to the seller while you still can, ask for full refund, and buy some other model of power supply.If you keep this one as it is, you'll never be sure why a tested circuit doesn't work as expected.

author: rdl
author_rank: Super Contributor
timestamp: December 17, 2023, 06:29:42 pm
content: That doesn't look good. If you're confident your testing set up was equivalent between the two, I'd send it back. As a replacement, I'd look for a linear supply. They are much more appropriate for lab use.

author: Kits
author_rank: Newbie
timestamp: December 18, 2023, 08:15:06 am
content: I've now returned it, had a busy day yesterday and decided to just get rid of it and maybe save up or get 2nd hand a proper power supply.For the set up, I only took one photo which isnt the final setup but you can see my layout.In the final setup, I had the alligator wires from from the power supply connected directly to the leds and the probes of the oscilloscope connected to the terminals of the power supply.I did try some repositioning and swapping the positions of the power supplies as the mains cable for the oscilloscope runs right next to the new one but I didn't seem to make much difference.The only interference I was able to confirm was that if I had both power supplies on at the same time, the new one would induce a multivolt ripple in my old one.This almost tricked me into thinking the new one was normal.Sorry I didn't wait for responses before pulling the trigger but I do apricate the help.

author: Kits
author_rank: Newbie
timestamp: December 18, 2023, 08:18:15 am
content: To answer Grandchuck question, the LEDS are just a dumb 12v strip no controller, no rgb, just LEDS and resistors.

author: mariush
author_rank: Super Contributor
timestamp: December 18, 2023, 08:58:20 am
content: With switching power supplies, you're supposed to limit the bandwidth to 20 Mhz and to add a capacitor right at the probe tips (something like a 10uF electrolytic in parallel with a ceramic capacitor)The long ground wires also don't help with the measurement, you'll pick up a bit of noise that will show up on the scope.You can find such recommendation in the ATX specification for power supplies (the 10uF and bandwidth limit on scopes)Here's an article that mentions these :https://www.amperordirect.com/pc/r-power-resource/z-reference-ripple-testing.htmlor this one :https://www.eetimes.com/power-tip-6-accurately-measuring-power-supply-ripple/

author: temperance
author_rank: Super Contributor
timestamp: December 18, 2023, 10:16:04 am
content: You bought a cheap power supply and expect from that supply top notch performance? Dream on.What you are seeing is common mode noise and cannot be filtered with differential filters.

author: Kits
author_rank: Newbie
timestamp: December 18, 2023, 10:35:10 am
content: my old power supply cost only £50, half of this one, I was expecting equal performance, ~30mVrms and <200mVpp. I don't think that's too much to ask for.The only think I dislike about my old one is the analogue controls. Maybe I got a lemon since the reviews are good but oh well.

author: radiolistener
author_rank: Super Contributor
timestamp: December 18, 2023, 02:22:13 pm
content: Quote from: RoGeorge on December 17, 2023, 06:00:32 pmJust recently I bought fast charge module on aliexpress for testing:https://www.aliexpress.com/item/32983839710.htmlit appears that it has 450 mVpp ripple... I think this is because it don't have ceramic capacitor on the output.But almost all buyers give feedback that this is good charger and working well...

author: CaptDon
author_rank: Super Contributor
timestamp: December 18, 2023, 02:59:25 pm
content: Look at the HUGE difference in ring frequency. The 'bad' power supply shows ringing in the MHz region. No wonder it apparently coupled into everything including your old power supply. Probably a lot of ground lead pickup of radiated noise. I notice on the old supply you have the negative output terminal bonded through the jumper clip to ground. The new supply doesn't seem to have that feature built in so you are comparing apples to oranges with your open spaghetti bowl wiring. You have discovered the main reason that for low power audio and analog projects I exclusively use analog linear power supplies that have no SMPS or triac/scr switching. Sometimes within reason when working at kilowatt+ levels there is an advantage to going SMPS like for instance not collapsing the workbench from the weight of a 3KW linear supply.

author: Kits
author_rank: Newbie
timestamp: December 18, 2023, 05:08:09 pm
content: Quote from: CaptDon on December 18, 2023, 02:59:25 pmYou actually have it backwards, the little one is my old one. I've already return the new one. That photo was the only one I had. the final setup that i used to make the print screens was a lot cleaner. power supply. connected directly to leds and probe connected to power supply terminals. In hindsight I agree i should have disconnected the jumper.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 18, 2023, 06:02:23 pm
content: Quote from: radiolistener on December 18, 2023, 02:22:13 pmWell, the lab supply in the OP has 5300 mVpp rippleYour charger is at least 10 times better than that.

author: Electro Fan
author_rank: Super Contributor
timestamp: December 18, 2023, 10:34:25 pm
content: It's very likely that there are some differences from one model to the next among power supplies (and possibly some unit to unit variation within a particular product model) but in order to get the best measurement there are some grounding techniques that can help get the best measurements.https://www.eevblog.com/forum/testgear/measuring-power-supply-ripple-with-siglent-1202x-e/msg5038294/#msg5038294

author: Kits
author_rank: Newbie
timestamp: December 20, 2023, 06:40:03 pm
content: So I thought I would add prob the final update for this thread. I started reading more about common mode interference.I'll first say that my original numbers still are solid and were not caused by common mode signals. I do think it was just a poor power supply and am now looking to get myself a linear supply.So I started experimenting with a probe that's only connected to it own ground lead to see what around my work area causes interference.I've a attached a photo of my office for reference.my base line with everything turned off except my pc came out at 500uVrms and 1.7mVpp.My first surprise was my main desk lamp. It being a led lamp and its proximity I expect it to be the worst but it generates nothing that I can detect.I assume it must use a linear supply or switch fast enough that it does cause a issue or maybe it runs the leds with 240v and dims them by cutting of the curve.This seems to hold true with everything else too, I couldn't find a single appliance with causes any noticeable change in interference.With one and only exception being my magnifying lamp, I assumed that since the lamp is very similarly designed to my main lamp it would use circuitry but I guess not.With the lamp turned on at a distance of around 50cm, I get 700uVrms and 12mVpp with a sharp 20khz spike. Thankfully when I took my original measurements it wasn't on.