When will the ripple increase

Smoothing and sieving


The rectifier circuit creates a strongly pulsating DC voltage. A capacitor is used to smooth this voltage. Most often an electrolytic capacitor with a high capacity. The voltage pulsation is largely prevented by this capacitor. The capacitor is called charging capacitor C.L. designated. One also speaks of capacitive loading.

Note: One should take into account that a single large electrolytic capacitor makes little sense. It is better to distribute the capacitance between two or more electrolytic capacitors. One capacitor should be connected to the bridge rectifier with the shortest possible conduction path and the other capacitor as close as possible to the consumer.


During the time the voltage rises, the capacitor charges up. The capacitor bridges the voltage gap between the half-waves.
The greater the capacitance of the capacitor, the better the smoothing.
The capacitance cannot be chosen arbitrarily high, since otherwise the high charging current of the capacitor would destroy the rectifier diodes.
The residual ripple of the smoothed alternating voltage is called ripple voltage. The ripple voltage UHum is the alternating voltage component of the smoothed alternating voltage. The ripple voltage is a measurable quantity that can be displayed with an oscilloscope.

The ripple voltage depends on

  • the capacity of the charging capacitor C.L..
  • the time (frequency) with which the charging capacitor is charged.
  • the size of the load / current consumption.

The ripple voltage is the smaller, the more

  • larger the capacity of the charging capacitor C.L. is.
  • greater the load resistance RL. or smaller the load current I.L. is by the load resistance.
  • greater the frequency of the ripple voltage UHum is.

Filter circuits / filter elements

The ripple voltage can be reduced with additional filter elements. Sieve and filter circuits should reduce the ripple voltage (alternating voltage component of a smoothed alternating voltage) as much as possible without significantly increasing the internal resistance of the entire circuit.

RC filter element


Through the resistance RS. and the second capacitor CS. the voltage fluctuations behind the charging capacitor C.L. even more balanced.
At higher currents, R arises at the resistors too great a voltage drop. It is better to use an LC filter element here.

LC sieve element


The LC sieving is due to the low coil resistance RKitchen sink very advantageous, but is used less often because of the size and weight of the reel.

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