The Ripple Factor
Although it is the purpose of a rectifier to convert alternating into direct current, idea circuit that we consider in our textbook doesn’t achieve this. Nor, in fact, do any of the more complicated rectifier circuits have a truly constant output. What is accomplished is the conversion from an alternating current into a unidirectional current, periodically fluctuating components still remaining in the output wave. It is for this reason that filters are frequently used in order to decrease these ac components. A measure of fluctuating components is given by ripple factor which is defined as ratio of rms value of alternating components of wave to average value of wave.
In order to measure ripple factor of a given rectifier system experimentally the measurement of the ripple voltage of the ripple current in the output should be made with the instruments that respond to higher power frequencies, so that the contributions from the higher – harmonic terms will be recorded. A capacitor must be used in series with the input to the meter in order to ‘block’ the dc components in the wave are recorded by the meter.
Effects of ripple
Ripple is undesirable in many electronic applications for a variety of reasons:
ripple represents wasted power that cannot be utilized by a circuit that requires direct current.
ripple will cause heating in DC circuit components due to current passing through parasitic elements like ESR of capacitors.
in power supplies, ripple voltage requires peak voltage of components to be higher; ripple current requires parasitic elements of components to be lower and dissipation capacity to be higher (components will be bigger, and quality will have to be higher).
transformers that supply ripple current to capacitive input circuits will need to have VA ratings that exceed their load (watt) ratings.
The ripple frequency and its harmonics are within the audio band and will therefore be audible on equipment such as radio receivers, equipment for playing recordings and professional studio equipment.
The ripple frequency is within television video bandwidth. Analogue TV receivers will exhibit a pattern of moving wavy lines if too much ripple is present.
The presence of ripple can reduce the resolution of electronic test and measurement instruments. On an oscilloscope it will manifest itself as a visible pattern on screen.
Within digital circuits, it reduces the threshold, as does any form of supply rail noise, at which logic circuits give incorrect outputs and data is corrupted.
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| Illustration : Ripple in circuits |
