Dear Engineers,
Today our contractor was doing a Vout ripple measurement on a scope on AC coupled setting. He was correctly using a “role your own" coaxial probe with narrow loop area. (no scope probe dangling ground clip).
The SMPS was a 5Vout DCDC module by XP. It was only supplying a load of some 5W.
I noticed his scope trace had the usual high frequency “pickup”, and the actual ripple voltage trace inside of this….kind of as in 4:33 of this video…
The high frequency pickup ringing pulses were at 50MHz. They had a peak-to-peak of 800mV
…Anyway, he was recording the peak to peak level of the high frequency noise pickup. (The 50MHz) Therefore, I informed him that he should ignore this ‘pickup’ and just take the actual output voltage ripple which is considerably less in peak-to-peak…..He then informed me that I was wrong, and that he should indeed record the high frequency ‘pickup’ peak-to-peak, because it gave in indication of how noisy the DCDC module was….
..So I then requested that he connect the scope ground and tip together, and then contact these to the 5V output terminal where he had been measuring the Vout ripple. I was expecting the high frequency ‘pickup’ to still be there…proving that it was simply ‘pickup’ induced into the scope probe…However, the “high frequency pickup” did indeed disappear from the scope trace….from which I had to conclude that the “high frequency pickup” was not actually induced into the scope probe, and that it was indeed a kind of “noise indication” pertinent to the actual DCDC module.
I then took an AC coupled measurement of vout just downstream of a ferrite bead at the output of the DCDC module.
(ie just downstream of the place where the first trace was taken. This second trace showed the peak-to-peak of the 50MHz ringing down 10 times to 80mV peak-to-peak)
What do you think?
This kind of thing is usually just “pickup”, and to be ignored?
JTK3048S05 datasheet
https://www.xppower.com/portals/0/pdfs/SF_JTK30.pdf
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Today our contractor was doing a Vout ripple measurement on a scope on AC coupled setting. He was correctly using a “role your own" coaxial probe with narrow loop area. (no scope probe dangling ground clip).
The SMPS was a 5Vout DCDC module by XP. It was only supplying a load of some 5W.
I noticed his scope trace had the usual high frequency “pickup”, and the actual ripple voltage trace inside of this….kind of as in 4:33 of this video…
The high frequency pickup ringing pulses were at 50MHz. They had a peak-to-peak of 800mV
…Anyway, he was recording the peak to peak level of the high frequency noise pickup. (The 50MHz) Therefore, I informed him that he should ignore this ‘pickup’ and just take the actual output voltage ripple which is considerably less in peak-to-peak…..He then informed me that I was wrong, and that he should indeed record the high frequency ‘pickup’ peak-to-peak, because it gave in indication of how noisy the DCDC module was….
..So I then requested that he connect the scope ground and tip together, and then contact these to the 5V output terminal where he had been measuring the Vout ripple. I was expecting the high frequency ‘pickup’ to still be there…proving that it was simply ‘pickup’ induced into the scope probe…However, the “high frequency pickup” did indeed disappear from the scope trace….from which I had to conclude that the “high frequency pickup” was not actually induced into the scope probe, and that it was indeed a kind of “noise indication” pertinent to the actual DCDC module.
I then took an AC coupled measurement of vout just downstream of a ferrite bead at the output of the DCDC module.
(ie just downstream of the place where the first trace was taken. This second trace showed the peak-to-peak of the 50MHz ringing down 10 times to 80mV peak-to-peak)
What do you think?
This kind of thing is usually just “pickup”, and to be ignored?
JTK3048S05 datasheet
https://www.xppower.com/portals/0/pdfs/SF_JTK30.pdf
Quote ReplyReport Edit
