Ripples in dc systems

Ripples are the constantly varying voltages found in the output of rectifiers. The output of a rectifier produces a pulsating voltage, which rises from zero to maximum Vp and then to minimum. This voltage is not suitable to be used in electronics as it contains ripples. The ripples need to be filtered by a filter circuit which is usually a capacitor connected in parallel to the power source.

Ripple factor

The amount of ripples in a dc source is indicated by the ripple factor which is defined as the ratio of the rms value of the ripple voltage to the absolute value of the dc voltage.

Ripple factor(γ)= (Vripple(rms)/Vdc)*100

Thus if we have 10V dc supply with a variation between 9.5 to 10.5 volts, the ripple factor would be (.5/5)*100 which indicates a ripple factor of 5%.

The peak-to-peak value of the ripples at the output of a full wave rectifier is given by


In the case of a half wave rectifier, the peak voltage is given by


where I is the current in the circuit, f is the frequency and C is the value of capacitance that is connected in parallel to filter the ripples

Measuring Ripples
Ripples can be measured in the field by an ordinary multimeter. Set the multimeter to measure AC voltage, and check the voltage at the output of the power supply. Any ripples would reflect as an AC voltage. Now, set the multimeter to dc voltage and measure the actual dc output. The Ripple factor is the ratio of the ac voltage to the dc voltage.

Effects of Ripples
Ripples can cause failure of components such as capacitors and can cause heating and failure in certain electronic components.
In audio circuits, the ripples can be reflected as noise, as the frequency of the ripples is within the audio band.
Ripples can also interfere in TV displays