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Calculate the Input/Output Capacitor Value on DCDC converter

stoui333

May 14, 2019
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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!
 

Harald Kapp

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Is there any mathematical formulas to find what capacitor values to use?
See page 12 of the datasheet.
Also, i have read that for the specific purpose (filtering/smoothing) better to use a ceramic capacitor instead of an electrolytic, is that right?
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

May 14, 2019
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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.

Thanks Harald kapp that was en lighting!
 

Harald Kapp

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I need to work on my spelling - or buy a new keyboard ;)
 
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