Siebelko-Seite (linear) auf Deutsch
Siebelko-Seite (linear) auf Deutsch

Minimum Capacity of a Filter Capacitor

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Vrms[V]

Transformer: Voltage of the secondary winding
Vdrop[V]

Voltage drop over the rectifier diodes
V-tol.[%]

Negative tolerance of the mains
Vdcmin[V]

Minimum required (DC-) voltage for the regulator
I[A]

Load current (output current + quiescent current)
tbridge[s]

Required bridging time
Note: at 50Hz 10ms would be ok but you would have no tolerance against voltage dips!


Vs[V]

Rectified peak voltage
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 lineary regulated devices which draw a nearly constant current over varying input voltage. For switch mode power supplies, which draw a nearly constant power, use this form!
All results without warranty!

©2009 Robert Loos