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    Default Test methodology

    Considering that in Croatia there is no quality review of PSU, I started testing with the PSU that is available in our market, mostly cheap one. I still have a lot of things missing (equipment), there are plenty of room for improvement but it will be... In the last test I compared the LC Power vs EVGA. Critiques, recommendations and advice are welcome.
    After the first test I saw that my test methodology does not match with most of that work and tests. I double checked but ..... first thing first....
    Ripple & Noise (PARD) - If I'm not mistaken ripple is mainly tested the ms range. I do not understand why, since the frequency of switch is substantially higher, suits us range?!
    Last edited by ITelektro; 10-18-2015 at 06:59 PM.

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    The 20 MHz bandwith is defined in the Intel psu design guidelines. Also the measurement procedure including the two small capacitors is described there.

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    Quote Originally Posted by Philipus II View Post
    The 20 MHz bandwith is defined in the Intel psu design guidelines. Also the measurement procedure including the two small capacitors is described there.
    Yes, bendwith limit must be set to 20Mhz but it has nothing to do with ripple freq.
    SMPS generally work in the kHz range (About 100kHZ), which corresponds to us(microsec) range, not ms(milisec.) range. ms range is freq from main power.
    PARD will be the frequency of the SMPS circuit, not Hz(ms) range.
    If the ripple is measured at the output capacitor there is no need to add up capacitors. And it is best way to measure ripple.
    https://www.youtube.com/watch?v=eVB_n4t57Yc
    https://www.youtube.com/watch?v=pKXPqApOYfk
    Last edited by ITelektro; 10-02-2015 at 04:53 AM.

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    Quote Originally Posted by ITelektro View Post
    Yes, bendwith limit must be set to 20Mhz but it has nothing to do with ripple freq.
    SMPS generally work in the kHz range (About 100kHZ), which corresponds to us(microsec) range, not ms(milisec.) range. ms range is freq from main power.
    PARD will be the frequency of the SMPS circuit, not Hz(ms) range.
    If the ripple is measured at the output capacitor there is no need to add up capacitors. And it is best way to measure ripple.
    https://www.youtube.com/watch?v=eVB_n4t57Yc
    https://www.youtube.com/watch?v=pKXPqApOYfk
    The voltage on the bulk capacitor has ripple at ~100Hz (2x the line freq). Since the DC/DC stage has a limited ripple suppression ratio at this frequency, part of that ripple may go through the entire DC/DC stage and remain in the DC output.
    It's been a hard day's night and I've been working like a dog.

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    Thanks for your reply. Your answer is correct, my question is perhaps a little imprecise.
    Do you think that the measurement ripple of SMPS in Hz range is more relevant than in kHz range?
    In the frequency range of the mains(50-60Hz) can not see a lot, it's boring line that goes down and up . But in the frequency range SMPS we can see a lot more. My question is, why Jonny selected first.
    One more thing, there is some PSU review that in CL test load at 3v&5v rails was 1A and some of them with 0A. Such a change in the test methodology will result in a a large difference in the results, especially when it comes to group-regulated power supply.
    According to the ATX design guide load should be 0.3A and 0.5A
    Am I missing something?
    Engrish is my second language, too

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    Quote 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)?
    Best, Luca

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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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    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)
    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.
    Quote 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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    Quote 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?
    Best, Luca

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    Quote 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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