Ripple Voltage and Ripple Factor

Definition of Ripple Voltages:

 Ripple voltages are the small undesired residual periodic variations of the DC (Direct current) at the output stage of the power supplies. These ripples are due to insufficient suppression of the alternating wave forms within the power supplies.

  • Large Ripple means less effective filtering
  • Smaller Ripple means more effective filtering.

Ripple Factor:

The ripple factor (r) is an indication of the effectiveness of the filter and is defined as

r= V r(pp) / V DC

where V r(pp) is the peak to peak ripple voltage and V DC is the dc (average) value of the filter’s output voltage.  The lower the ripple factor, the better the filter.  The ripple factor can be lowered by increasing the value of the filter capacitor or increasing the load resistance.

For a full wave rectifier with a capacitor input filter, approximations for the peak to peak ripple voltage, V r(pp) and the dc value of the filter output voltage, V DC, are given in the following expressions.  The variable V p(rect) is the unfiltered peak rectified voltage.

V r(pp) = (1/fRLC) Vp(rect)

V DC = (1- 1/2fRLC) V p(rect)

 

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