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    Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    Hello,
    We are doing an SMPS using the DCM3623T50M53C2T00 Vicor DCDC module.
    Please assist us in getting at least 10mR of ESR in our external output filter.
    What we currently have is as attached.

    PSU Spec:
    ……………………………………….
    Vin is 33V
    Vout is 48V
    Pout is 288W
    Crossover frequency of DCM module is 20kHz.
    The DCM module switches at ~750kHz
    This DCM module comprises an internal output capacitor of 11uF with 0.222R of ESR.
    There must be a minimum of 200uF of external output capacitance (max of 2000uF)
    ……………………………………………….

    The DCM datasheet rules that there must be a minimum of 10milliohms of ESR in the external output capacitance.
    Our output filter is as in the attached.
    The biggest capacitor there is the 1mF MAL203859102E3 capacitor from Vishay…………….

    MAL203859102E3 capacitor:
    https://docs.rs-online.com/6f7a/0900766b80d99217.pdf

    …there is no way of calculating this capacitor’s ESR from the info given in the datasheet.
    Tan delta is only given for 100Hz….with that value, the ESR comes out as 17.8 microOhms…nowhere near the amount required.
    We do not have a frequency analyser and have no money to buy one , so we cant measure ESR for any of our output capacitors.

    Do you believe the best way for us to ensure we have at least 10 milliohms of ESR in the output filter is to literally place a 100mR , 2512 resistor in series with each of our three electrolytic output capacitors?

    DCM3623T50M53C2T00 Vicor DCDC module datasheet
    http://www.vicorpower.com/documents/...53C2yzz_ds.pdf

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    Re: Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    In fact, In order to ensure that the DCDC module always effectively “sees” at least 10millOhms of ESR…could we add a series resistor into the output as in the attached pdf file called “SMPS output filter ESR”?



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    Re: Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    Say you use 1000uF on the o/p, ues 2 x 470uF low ESR

    put 10 milli-ohm in series with one of them - job done - it will be stable ...



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    Re: Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    thanks, im obviously missing something here, but wouldnt the cap with no esr placed in series with it, partially short out the esr that had been placed in series with the other one?



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    Re: Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    One milliOhm is incredibly small, the chances are the ESR of the capacitors is higher than that already and the added resistance of the connection to it will make up any difference anyway. I don't think I've ever seen a physical resistor used to increase ESR and to implement one would probably only involve a few mm of extra PCB track anyway.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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    Re: Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    but wouldnt the cap with no esr placed in series with it, partially short out the esr that had been placed in series with the other one?
    Partially, yes. You need to calculate the total ESR of the C-RC combination at 11 kHz. A slightly higher resistance value, e.g. 20 mohms could be necessary - if the capacitor ESR is actually that low.

    Your loss factor calculation in post #1 is totally flawed. I get > 100 mohms ESR with tan δ 0.08 for the said 1000 µF/100V capacitor, which sounds realistic for a capacitor that's not specified as low ESR. Means your worries are pointless.



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    Re: Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    thanks, at 20khz, I get ESR = "tan d" * Xc = 637microohms for a 1000uF cap and tan d = 0.08 and 20khz



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    Re: Need to ensure SMPS output filter has at least 10mR of ESR...use "ESR resistor"?

    That's not how you calculate it. Loss factor is specified for 100 Hz. ESR is decreasing between 100 Hz and 10 kHz, but not more than several 10 percent.



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