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Old 01-26-2017
ITelektro ITelektro is offline
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Originally Posted by crmaris View Post
I use both an isolation transformer and an AC source. Clean voltage is the key
Define term "clean voltage", please.

Ripple below 10mV is of less importance according to my opinion. What if you measure 5mV and it actually is 7 or 8mV.
4mV and 8mV, double difference is not irelevant. It is only if its easy for PSU manufacturer to archive that. Is it? I dont think so.
I suggest in order to constructive discussion leave personal opinion beside.
Hope for link or screenshoot of measurement.
On top of that you even will lose that if you don't use a logging software to monitor the entire load test (which can last from 5-15 minutes at a time) and have in hand the entire ripple session of the PSU (with a good scope you might be able to bypass this though).
I agree...Logg. software is one way. Another way is statistics option that lot modern scopes have.

I have a good set of differential probes, only use it to measure dangerous (very high voltage) stuff. I am aware of the affordable diff probe solutions, since I searched about the rebranded models that are on the market before I acquired mine
I think that you understand this well, but it can confuse some young players.

High voltage differential probes are not suitable tool for ATX PSU ripple measurement. Attenuation ratio probe is typically more than 20x(10x,20x,100x,1000x)..... Signal will be attenuated by factor of 20 and noise will be multiplied by same factor.
So, for low amplitude signals like ripple (for modern ATX PSU) high voltage differential probe is not recommended. It is same case like 10x passive probe.
Second thing is, high voltage differential probe has significantly lower CMRR(Common-mode rejection ratio). Typically 1:100 while low voltage diff. probe has ratio 1:3000.
All this is like tolls in workshop. We have screwdrivers, hammers, wrenches... We use tool that is suitable for job.
There is no way to get absolute precise results, but its important to know limitation of tools that has been used.
Regarding that, "clean source or no clean source" will affect results, more important is how much expressed in mathematical form rather then like opinion.
Like we can see, in some cases probing techniques and probe selection will significantly affects results. In some cases 30% and more. Is this relevant? We can argue, but it is fact not opinion.
For cheap and good option I thought of 50ohm path. I have pick up all components from local electronic store, will post here results soon.
ATX spec recommends lots of stuff, however I seriously doubt if an electronics engineer has written it or checked it (at least the latter versions). See the silly high ripple limits that it has for example, which remain the same for many years now.
I dont know, Crmaris. Even I repaired aprox 10k motherboard I am not convinced to put credibility engineer that has written that document. I need good reason for that.
I have good example. Santa rosa platform and Merom CPU on Toshiba motherboards. Most common problem is capacitor on Vcore voltage. System will be stable untill ripple exceed 100mV, its about 10%. First conclusion is, motherboard are not so sensitive to ripple voltage.
Second thing is design standard. If is motherboard designed to handle that amount of ripple and work stable there is no problem, it should be.
I agree, lower is better but its not about that, its about what is enough regarding motherboard design.
There is one thing to consider too, influence on capacitor life....
However, reason for differential probe recommendations still stays as best option for making low voltage measurements.

Last edited by ITelektro; 01-26-2017 at 05:15 PM.
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