EEVblog #594 - How To Measure Power Supply Ripple & Noise
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange answerers and commenters point people to it when ripple or noise readings on a switching supply look suspiciously large, because it shows how the probing technique itself can fool you.
Recommended by 3 people across 4 different months, 2015 to 2019.
What it is
A 38-minute EEVblog 'Fundamentals Friday' episode in which Dave Jones explains what power supply ripple and noise specifications mean and how to measure them on analog and digital oscilloscopes. He walks from poor probing techniques to good ones, covering single-ended vs differential measurement, DIY coax solutions, termination, bandwidth limiting and common mode noise.
What people said
Recommends zipzit · 2015-11 · Electrical Engineering Stack Exchange · on “Source of Audio Noise at Low Volume -- BlueTooth Mini Amp board”
Just finished up the 40 minute video at [this video] Interesting, and I'm obviously not doing it exactly perfect. Not sure that will make a huge difference in this situation. I will say, my suspicion is that the noise here is coming from the Bluetooth circuit, pre-amp. The reason for me saying that is I've seen the same board as I've got, with additional capacitors located between the bluetooth module and input to the class D amp. (I suspect design phase 2?)
Recommends Paul Uszak · 2017-05 · Electrical Engineering Stack Exchange · on “Power supply noise issue”
Noise seems high although as some have suggested if it works, why fix it? The Pi will have it's own bypassing capacitors that mitigate this noise. You're clearly using a commercial /professional switch chip rather than some Frankenstein 555 timer creation. The chip's data sheet has layout recommendations towards it's end. These are pretty important due to the large switch currents flowing around (and beneath) the chip. Do these recommendations match yours? I'm assuming that your circuit is lifted straight from the data sheet. So you might expect the same ripple /noise that it gives. I can't read the screen sufficiently on my device to ascertain the noise, but is it ~30mV @ 20 MHz? I'm not su
Recommends winny · 2018-08 · Electrical Engineering Stack Exchange · on “Class D power supply filtering for conducted emissions”
Ah! Rookie mistake. At 340 kHz it might not be the world but changing the decoupling there and remeasuring that mV signal will suffer and be hard to draw conclusions from. Please see Dave’s eevblog on the subject here: [this video]
Recommends winny · 2019-06 · Electrical Engineering Stack Exchange · on “Filtering power supply noise”
It sure should. You will however fool yourself in terms of absolute numbers for your ripple unless you have adequate probing. The relative improvement you will however catch. Here is the video: [this video] Fast forward to 18:47 if you don’t want to watch the whole thing.
Cites Liquid Plasmas · 2019-11 · Electrical Engineering Stack Exchange · on “Massive pk-pk ripple on output using isolated DC-DC converter module”
It's been some time since I opened this question but I wanted to share the ultimate solution to help others new to diagnosing switching mode power supply characteristics (many of the comments helped but @VoltageSpike and @Elliot Alderson really set me on the right path). In the end this was mostly a matter of not understanding how to probe the transient voltages produced by an SMPS properly with an oscilloscope. After reviewing several different references: EEVBlog bypass capacitor overview: [LINK] EEVBlog grounding strategies for single ended oscilloscope probes: [LINK] EEVBlog measuring power supply ripple and noise: [this video] CUI's guide on measuring ripple and noise with single ended probe