EEVblog #594 – How To Measure Power Supply Ripple & Noise

Fundamentals Friday
Dave explains what the ripple and noise specifications on a power supply is and how to measure it using different methods on both analog and digital oscilloscopes. From bad techniques through to good, showing the effect of each one. Traps for young players aplenty in this one.
How do you detect common mode noise issues and ensure that the signal you are measuring is really coming from your device under test?
Single ended & differential measurement, DIY coax solutions, termination, analog vs digital oscilloscopes, bandwidth limiting, and even oscilloscope probe coax construction issues. It’s all here.
Mysteries of X1 oscilloscope probes revealed
How to track down common mode noise
Opamp Noise voltage tutorial
Forum HERE

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    • Glad to see that Fundamental Fridays are back! This stuff always makes me think and I’ve actually have used some of what Dave has taught me, Brilliant!

    • Kym

      Hi All,

      A timely video blog for me!. I’ve successfully measured PSU ripple and noise with a Tektronix ADA400A differential amplifier, bandwidth limited to 1MHz, down to about 10uV pk-pk. Admittedly the ADA400A is not too cheap, but very very useful.

      I also noted that a lot of DMM’s with mV AC ranges, ie Agilent 34401a, and Rigol DM3068 (which I use) FAIL to measure AC below about 1 mV AC RMS even though on the 100mV range which has a resolution of 0.1uV!

      Interestingly my Agilent U1272A works very well down to 20uV AC RMS (needs offset null at those levels though).

      • Wim Libaers

        This may be normal and expected depending on the true RMS technique used. Most true RMS multimeters never go down to zero on the AC range, and their specifications are only valid above a certain minimum voltage level.

    • Chris

      Thanks Dave,
      Really interesting and I learned a lot. I was wondering though, is there a simple circuit one could add to a lousy power supply to help reduce the noise and ripple? Or just stick a big capacitor in there?

    • Paul

      What a brilliant video, I need to buy a more modern scope, mine is only 10mhz bandwidth,
      I was going to go for a digital, but I think I’m going for another analogue with say a 200mhz bandwidth. It’s really nice to see Dave use both,in real time so to speak.

    • Hi,

      Thanks again for this nice video.

      Maybe an idea for a next video : “how to track noise and hum in an audio circuit”



    • tchicago

      Dave, the Rigol 1000Z scope shows a clear horizontal artifacts on the waveform display, for example at 13:20. What is this? Some special mode that puts a vertical grid on top of display, or some kind of a software bug?

    • Lefuneste

      Wow thanks Dave !! This video was really informative for “young players” like me. Especially since I started designing power supplies for audio and was always fighting to get proper reading of my noise values. Really helpful !!

    • ViliusR

      BIG THANKS from one young player!

      had familiar “problems” recently with my power supply, and it appears to be incorrect measurement techniques. doh!

      anyways, have an overengineered power supply now 😀

    • huh

      What is the name of those springy contacts you fix on the scope probe ground to test SMD’s? I’ve bought a couple sets of probes recently and they weren’t supplied. Thanks.

    • Rick Loveman

      You did not mention the ultimate differential probe: A transformer.
      Choosing a good transformer completely eliminates common mode noise even a single ended connection to a transformer can perform very well. It actually works as a balun.

    • Laurent

      Hi dave,

      you catch quite a lot of noise from your Led litghing…
      What is the EMC compliance standard in austraaalia? CISPR?
      It would be fun and really interresting to try to verify the leds in an EMC labs and maybe try to fix their switching issues.
      Don’t you think?
      I know the lab time is really expensive but, maybe you will find a generous university lab which can understand the educationnal side of your blog.

      Kind regards

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