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Calculate the Input/Output Capacitor Value on DCDC converter

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

  1. stoui333

    stoui333

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    0
    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. Harald Kapp

    Harald Kapp Moderator Moderator

    9,293
    1,884
    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. stoui333

    stoui333

    7
    0
    May 14, 2019
    Thanks Harald kapp that was en lighting!
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    9,293
    1,884
    Nov 17, 2011
    I need to work on my spelling - or buy a new keyboard ;)
     
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