Siebelko-Seite (SPS) auf Deutsch
Siebelko-Seite (SPS) auf Deutsch

Minimum Capacity of a Filter Capacitor

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Vrms[V]

Lowest acceptable RMS-value of the input voltage
Vdcmin[V]

Minimum required(DC-) voltege for the converter
P[W]

Input power of the converter (output power / efficiency)
tbridge[s]

required bridging time
Note: at 50Hz 10ms would be ok but you would have no tolerance against voltage dips!
Also consider allowable under­voltage (mains has typically -10%) as well as voltage drop over the rectifiers and the EMI-inductor!

Us[V]

Rectified peak voltage of the filter capacitor
Cmin[F]

Minimum required value of the filter capacitor to keep the voltage above Vdcmin during the bridge time.
Advice: use at least twice this value! Capacitors have tolerances and loose capacitance by aging!
This calculation is only valid for switch mode power supplies which draw a nearly constant power over input voltage. For linearly regulated supplies, which draw a nearly constant current, use this form.
All results without warranty!

©2006 Robert Loos