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Thread: Seasonic X-650 650W Review

  1. #21
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    Quote Originally Posted by Oklahoma Wolf View Post
    thanks OW!!
    The CM6901x combined PWM (or they called SRC) and LLC function together and it's looks good for the light load efficiency and high load ripple/noise, do you see any PSU use the same chip?
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    Last edited by ef3393; 04-10-2011 at 01:37 AM.

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    Quote Originally Posted by ef3393 View Post
    do you have CM6901X application note or do you know how to find it, as I know the LLC resonant have lower switching frequency during high load and very high switching frequency during low load but it's not a PWM mode, are you sure the controller could switch to PWM mode during low load? I am not sure if the low frequency PWM will help on the efficiency than a high frequency soft switching?
    http://www.champion-micro.com/product-en/CM6901.htm

    Light Load regulation is accomplished by transitioninig the controller from frequency modulation mode to PWM mode.
    It's been a hard day's night and I've been working like a dog.

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    Quote Originally Posted by ef3393 View Post
    thanks OW!!
    The CM6901x combined PWM (or they called SRC) and LLC function together and it's looks good for the light load efficiency and high load ripple/noise, do you see any PSU use the same chip?
    Not yet. CMC has been promoting CM6900 solution for more than one year but its a bit (cough) buggy.
    It's been a hard day's night and I've been working like a dog.

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    Interesting controller chip (switching between PWM and FM). Any idea on what the FM would accomplish? I would hazard a guess that the FM somehow ties in with minimizing jitter in the PWM feedback look.
    Software readings are crap.

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    Quote Originally Posted by Super Nade View Post
    Interesting controller chip (switching between PWM and FM). Any idea on what the FM would accomplish? I would hazard a guess that the FM somehow ties in with minimizing jitter in the PWM feedback look.
    No, at light loads it gives up on the efficiency and low noise of resonant operation in order to maintain a minimum switching speed. That, in turn, avoids excessive ripple at light loads.

    Think of a switching power supply as a piston pump. Each time you work the handle, a certain amount of water (charge) comes out. You have to adjust the pumping to maintain a flow rate (current) equal to the drain rate, or the water level will rise (overvoltatE) or fall (undervoltage).

    Normally, it regulates by adjusting the rate of pumping. But at low flow rates, the rate would be very low and there would be a lot of ripple if you used full pump strokes.

    So instead, the controller switches to useing short pump strokes, so it can keep the pumping frequency high enough to avoid excessive ripple.

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    I suppose before that, what is not clear to me is, how are FM and PWM essentially different? When you vary the pulse width (time domain) are you not changing the frequency BW/center freq as well (freq domain)?
    Software readings are crap.

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    Quote Originally Posted by Super Nade View Post
    I suppose before that, what is not clear to me is, how are FM and PWM essentially different? When you vary the pulse width (time domain) are you not changing the frequency BW/center freq as well (freq domain)?
    BW is mainly affected by rising edge and falling edge.
    It's been a hard day's night and I've been working like a dog.

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    Quote Originally Posted by Super Nade View Post
    I suppose before that, what is not clear to me is, how are FM and PWM essentially different? When you vary the pulse width (time domain) are you not changing the frequency BW/center freq as well (freq domain)?
    The three values (on time, off time, and cycle time) are related, but in classic PWM, the cycle time is held fixed, so all that changes is the fraction of the cycle which is switched on.

    Another alternative is to have a fixed on-time or off-time. Varying the other causes the switching frequency to change. This is typical of resonant controllers because each on-cycle causes the resonating components to "bounce" once.

    But when the off-time reaches a maximum, it gives up on resonant operation and starts reducing the on time.

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    Switching to FM for low demand states is a novel & inexpensive way to overcome the inherent problems associated with using PMM for low demand states.

    Great idea, which is of course now obvious.
    Yes. One of the last commincations I had with Dave Hammock before he disappeared from the web was how a major brand single +12V rail PSU wasn't shutting down when shorted. We were literally arc welding with the PSU. Hopefully Dave's absense isn't due to the fact that he got over zealous with the welding.
    JonnyGURU Posted 4-1-08

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    Quote Originally Posted by davidhammock200 View Post
    Switching to FM for low demand states is a novel & inexpensive way to overcome the inherent problems associated with using PMM for low demand states.

    Great idea, which is of course now obvious.
    What you're describing is exactly the opposite of how this PSU works. It uses PWM mode under light loads and FM at higher ones.
    Main: i5 2500K@4.6GHz w/Zalman CNPS10X Performa, Intel DZ68BC, 8GB G.Skill DDR3-1600, PNY GTX 470 + EVGA GTX 470, ASUS Xonar DX, ADATA S510 120GB, Samsung 1TB F3+1TB F1+2TB F4, Kingwin LZG 1kW, Lian-Li PC-9F, Dell U2212HM+S2209W, Win7 Professional.
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