View Single Post
Old 01-25-2017
ITelektro ITelektro is offline
500W User
Join Date: Jul 2015
Location: Croatia
Posts: 70
Thanks: 12
Thanked 9 Times in 8 Posts

Originally Posted by crmaris View Post
when you measure ripple the most important is to provide a clean source! If not then what ever you use, differential or normal probe, will be rendered useless.
Maybe, but first of all we must define what is clean source or, in other words what is not clean source.
Every PSU have some PSRR (power supply rejection ratio) so noise will be reject depend of that value. I think, the difference between measured ripple of PSU on Croma source and PSU on isolating transformer will be negligible.

For me differential probes aren't needed.
In some cases, I agree. But in some other cases measured ripple results will be at least twice high depend of technique and probing solution.
In ripple measurement oscilloscope and probing solution must be defined or test results are questionable since they cannot be reproduced.

Worst case scenario is;
Attachment 2497
10X probe VS Diff. Probe. (scope is calibrated, differential probe is verified on calibrated instrument (rigol dg1022)).
If ripple is lower amplitude, difference in results will be even higher.
This is important for newer PSU, because we can expect lot of PSU whit ripple lower than 10mV. Signal to noise ratio on 10x probe will be even higher.
This is example;
Attachment 2499
Solution like 1x or 2x probe will give lot better results but only in case if probe have enough bandwidth.
Attachment 2498
Here we can se 100mV 20Mhz signal measured with 1X probe 7Mhz bandwidth.
Even signal is 100mV measuring results is only 31.5mV.
There are some cheap and good solution but I will leave that for some other time.
So, yes 10x probe is in some case good enough but all this above is a reason why Intel specs recommends differential probe.

Last edited by ITelektro; 01-25-2017 at 12:21 PM.
Reply With Quote