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Calculate the Input/Output Capacitor Value on DCDC converter

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Discussion in 'Power Electronics' started by stoui333, May 14, 2019.

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  1. May 14, 2019 #1
    stoui333

    stoui333

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    May 14, 2019
    Hi everyone,

    I have a general question on how to calculate the input and out capacitor values for a DCDC converter for filtering/smoothing.

    My example:

    DCDC Converter: Synqor NQ60W60QTC25NRS
    Input Voltage: 36v
    Output Voltage: 12v
    Load: 5A

    Is there any mathematical formulas to find what capacitor values to use?
    Is there any rule of thumb?

    Also, i have read that for the specific purpose (filtering/smoothing) better to use a ceramic capacitor instead of an electrolytic, is that right?

    Thanks in advance for your answers!
     
  2. May 14, 2019 #2
    Harald Kapp

    Harald Kapp Moderator Moderator

    11,413
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    Nov 17, 2011
    See page 12 of the datasheet.
    No. Electrolytics and ceramics serve different purposes:
    • Electrolytics with their high capacitance serve to buffer a lot ocg charge to provide high currents for a long time (comparatively).
    • Ceramics with their low capacitance baut also very low ESR to filter primarily high frequency noise.
    Usually a combination of both types (and even ceramics of different capacities) is used to cover a wide range of frequencies. See e.g. here.
     
    stoui333 likes this.
  3. May 15, 2019 #3
    stoui333

    stoui333

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    May 14, 2019
    Thanks Harald kapp that was en lighting!
     
  4. May 15, 2019 #4
    Harald Kapp

    Harald Kapp Moderator Moderator

    11,413
    2,619
    Nov 17, 2011
    I need to work on my spelling - or buy a new keyboard ;)
     
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