I'm having some trouble with a "cheap and cheerful" bench power supply that I become an owner of. When scoping the outputs I'm seeing some really high noise peaks (see attached photos) in the region of +/- 5V at around 66MHz when outputting 3.8V! Now interestingly when I connect the scope probes to the ground terminal on the scope and switch the power supply on, the same sort of noise appears on the scope, which leads me to think that the power supply is kicking out some noise down the 230V power input neutral which is then throwing the scope off. I also get a crackling sound from my speakers when the power supply is on! Are there any modifications that I could do to the power supply to reduce this noise?

Any input would be much appreciated!

Scope output at 3.8V

enter image description here

Update: I've run the scope with a 10ohm load across the power supply running at ~4V and this seems reduce those massive noise peaks across the neutral. However, when scoping the actually supply this is the result I get (and that's with a decoupling cap in parallel with the load!):

enter image description here

So another thing I've noticed, when turning voltage on the power supply down with an open load, a (quite noisy volume wise) transformer turns off (I assume to let the smoothing capacitors discharge a bit). During this time there is no electrical noise at all, however when the noisy transformer kicks back it the electrical noise comes back.

  • \$\begingroup\$ Quite strange, even for a cheapie. What model is this? Is it a linear or a switcher design? \$\endgroup\$ – anrieff May 4 '18 at 2:08
  • \$\begingroup\$ Does the noise change when you load the supply? Above measurements taken with the supply open circuit? \$\endgroup\$ – AlmostDone May 4 '18 at 2:58
  • \$\begingroup\$ Could you post a picture or website link to the power supply page? \$\endgroup\$ – skillz21 May 4 '18 at 3:24
  • \$\begingroup\$ If you put some load on it, do you still see the same? Many cheap buck regulators go into trickle-mode if the load is less than normal cycle of inductor. \$\endgroup\$ – Ale..chenski May 4 '18 at 3:53
  • \$\begingroup\$ It's a QW-MS3010D (the 10A version of this ebay.co.uk/itm/…). See edit for scope pictures with load \$\endgroup\$ – someguythatcodes May 4 '18 at 8:26

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