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Testing Methodology Discussion Questions and comments regarding the testing methodologies used on jonnyguru.com

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  #11  
Old 10-26-2015
ITelektro ITelektro is offline
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Quote:
Originally Posted by Behemot View Post
What link? I do that as a part of my job, I guess after couple tens of units I have some idea how it looks.
I do not think so, at least not according to what you writing. Let me remind you;
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You may not see that optically but the O-scope calculates it from the whole window. If you choose too small window it just won't
As you can see from previous post, my scope calculate ripple just fine. My "window" is not small it fit just perfect because ripple freq of switch power supply is 75kHz, not 100Hz.
I did not expect to actually have to explain what is ripple of switch power supply. I'm a little disappointed.
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You did not see that in school, at least the basics?

https://www.youtube.com/watch?v=Edel3eduRj4
This guy measure ripple of switch power supply at 5us/div.
https://www.youtube.com/watch?v=pKXPqApOYfk

Once again, freq of ripple on switch power supply is same as freq of PWM oscillator. On ATX power supply is about 100kHz. You cant see that ripple and noise of switch power supply if time base is set at 20 ms/div. You missing information.
My question is simple but requires a concrete answer and link of relevant source; (see first post)
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  #12  
Old 10-26-2015
Behemot Behemot is offline
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Eh? You can yourself see it does not work when being on too short time frame.

Anyway, you do whatever you want…do you even have decouplers there?
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  #13  
Old 10-27-2015
ITelektro ITelektro is offline
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Eh? You can yourself see it does not work when being on too short time frame.
Anyway, you do whatever you want…do you even have decouplers there?
Behemot thank you for replay, but i did not get answer for my question.
In previous posts I've included some links that explain on easy and understandable way test methodology SMPS power supply.
Must add this one too;
https://www.youtube.com/watch?v=ZG7SV3pdJe4
If you have any kind of questions just ask.
I had, just one, hope I can still get an answer for my simple question.
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  #14  
Old 10-27-2015
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You got your answer from several people, all of whome have long experience testing power supplies. Yet you still do not accept any of that and throw some general crap at us, I repeat, people who test power supplies for a long time. At the same moment when your results are inconsistent with the rest of the UNIVERSE. Yet you are still arrogant and talk about some begginers videos about ripple like it was ground-breaking true.

I can guarantee you one thing - none of us here has ANY FRELLING IDEA how the ripple is exactly generated in the supply. Tens of variables come in play and they ALL AFFECT THE RESULT. Power supplies are so complicated that even people who make them THEIR WHOLE LIFE often struggle creating good product as the real-world computers, electric lines etc. often come back and kick their effort. Best we can do is to measure something and than talk about it.

Do you have differential probe? Do you have decouplers and what are they? Where do you measure? Do you have all connectors plugged into something? These all things come into play. Not even the norm specifies all of them and they pretty much heavily affect the results. We all mostly don't talk about the fact none of us (correct me if I am wrong) has differential probe but as long as our results are +- the same, we can expect we are around the area of the corect results. If you have completelly different results, either we all others do it wrong, or you do it wrong. I bet on you.

I think I yield right here.
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  #15  
Old 10-27-2015
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Originally Posted by ITelektro View Post
Do you think that the measurement ripple of SMPS in Hz range is more relevant than in kHz range?
Uhm, just a noob question (I'm paraphrasing your own words): why do you think that an higher frequency will be useful (or more correct/suitable)?
Which important figures can you see in the kHz range (which you will miss in the Hz range)?
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Old 10-27-2015
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None, it is quite the opposite - if you look too close, you miss the bigger picture. This si somewhat general principle I think…
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Old 10-27-2015
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Quote:
Originally Posted by quest for silence View Post
Uhm, just a noob question (I'm paraphrasing your own words): why do you think that an higher frequency will be useful (or more correct/suitable)?
Which important figures can you see in the kHz range (which you will miss in the Hz range)?
Primary switching frequency artifacts. There is however an AC component from main line, the one that went all the way from power grid, and hasn't been perfectly filtered out, obviously at 50-60 Hz.

IME setting time div to us range to match switching frequency does show them, but that AC component is just waving up and down.
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  #18  
Old 10-27-2015
ITelektro ITelektro is offline
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Quote:
Originally Posted by quest for silence View Post
Uhm, just a noob question (I'm paraphrasing your own words): why do you think that an higher frequency will be useful (or more correct/suitable)?
I dont think so
We're looking for the worst case scenario. I prefer both. These two measurements do not necessarily give the same results.
When you measure ripple of SMPS it can only be at same freq. as PWM, according to previous links. (keyight, tektronix, texas instruments,eevblog)
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Which important figures can you see in the kHz range (which you will miss in the Hz range)?
Noise and freq of PWM. Let me explain;



Switching ripple noise is created when a switch-mode power supply and associated load charges and discharges the output capacitor, respectively, during every cycle of the pulse-width modulator (PWM) engine. The frequency will be that of the PWM oscillator and often looks like a triangle wave. end of quote; http://www.edn.com/design/power-mana...oise--Part-2--
At point 1(red) switching element is turning on and starts to charge output capacitor. At point 2(blue) switching element turns of and output capacitor is discharging, voltage goes down till next cycle. When switching element change his state it will make some noise(spikes at that point) caled switching transient noise . You can see freq and ripple at meas. tab.
You will miss all that at ms range, cant see any of this.
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Originally Posted by rafal_iB_PL View Post
Primary switching frequency artifacts. There is however an AC component from main line, the one that went all the way from power grid, and hasn't been perfectly filtered out, obviously at 50-60 Hz.
IME setting time div to us range to match switching frequency does show them, but that AC component is just waving up and down.
This is correct. The question is; what we want to measure. In us range we can see SMPS ripple, u ms range leftovers of ac component from grid.

@Behemot
Thanks for your replay.
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  #19  
Old 10-28-2015
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Originally Posted by ITelektro View Post
You will miss all that at ms range, cant see any of this.
But, if I understood correctly, even when you don't see it (in the ms timescale), the scope will still take account of it when recording output ripple figures: won't it?
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Old 10-28-2015
ITelektro ITelektro is offline
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Originally Posted by quest for silence View Post
But, if I understood correctly, even when you don't see it (in the ms timescale), the scope will still take account of it when recording output ripple figures: won't it?
I think no.
3024T has power analysis option, but most of scopes does not have this feature. Ripple is measured by standard pk-pk measurement usually with cursors tracking(manually or auto). IMO, what you see on display of that scope it will be measured. There is only one way to find out, test in lab. I have here PSU to test, Antec. Will post results here.

My English is bad but I hope I was able to explain what is SMPS ripple and how it occurs, if there is any questions....
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