Ripple (electrical)
Ripple (specifically ripple voltage) in electronics is the residual periodic variation of the DC voltage within a power supply which has been derived from an alternating current (AC) source.
Ripple voltage originates as the output of a rectifier or from generation and commutation of DC power.
As well as these time-varying phenomena, there is a frequency domain ripple that arises in some classes of filter and other signal processing networks.
Various properties of ripple voltage may be important depending on application: the equation of the ripple for Fourier analysis to determine the constituent harmonics; the peak (usually peak-to-peak) value of the voltage; the root mean square (RMS) value of the voltage which is a component of power transmitted; the ripple factor γ, the ratio of RMS value to DC voltage output; the conversion ratio (also called the rectification ratio or "efficiency") η, the ratio of DC output power to AC input power; and form-factor, the ratio of the RMS value of the output voltage to the average value of the output voltage.
Reducing ripple is only one of several principal considerations in power supply filter design.
Therefore, large discrete components like high ripple-current rated electrolytic capacitors, large iron-core chokes and wire-wound power resistors are best suited to reduce ripple to manageable proportions before passing the current to an IC component like a voltage regulator, or on to the load.
The kind of filtering required depends on the amplitude of the various harmonics of the ripple and the demands of the load.
For example, a moving coil (MC) input circuit of a phono preamplifier may require that ripple be reduced to no more than a few hundred nanovolts (10−9V).
In contrast, a battery charger, being a wholly resistive circuit, does not require any ripple filtering.
The filtering requirements for such power supplies are much easier to meet owing to the high frequency of the ripple waveform.
[citation needed] A capacitor input filter (in which the first component is a shunt capacitor) and choke input filter (which has a series choke as the first component) can both reduce ripple, but have opposing effects on voltage and current, and the choice between them depends on the characteristics of the load.
Choke input filters are preferred for circuits with variable loads and high currents (since a choke outputs a stable voltage and higher current means less ripple in this case).
Resistive components (including resistors and parasitic elements like the DCR of chokes and ESR of capacitors) also reduce signal strength, but their effect is linear, and does not vary with frequency.
A common arrangement is to allow the rectifier to work into a large smoothing capacitor which acts as a reservoir.
At that point the rectifier conducts again and delivers current to the reservoir until peak voltage is again reached.
If the RC time constant is large in comparison to the period of the AC waveform, then a reasonably accurate approximation can be made by assuming that the capacitor voltage falls linearly.
In this case the phase angle through which the rectifier conducts will be small and it can be assumed that the capacitor is discharging all the way from one peak to the next with little loss of accuracy.
is taken from start of capacitor discharge until the minimum voltage on a full wave rectified signal as shown on the figure to the right.
A choke has a filtering action[clarification needed] and consequently produces a smoother waveform with fewer high-order harmonics.
There is a minimum inductance (which is relative to the resistance of the load) required in order for a series choke to continuously conduct current.
Additionally, interrupting current to an inductor will cause its magnetic flux to collapse exponentially; as current falls, a voltage spike composed of very high harmonics results which can damage other components of the power supply or circuit.
The complex impedance of a series choke is effectively part of the load impedance, so that lightly loaded circuits have increased ripple (just the opposite of a capacitor input filter).
The ripple factor is where Similarly because of the independence of LC filter sections with respect to load, a reservoir capacitor is also commonly followed by one resulting in a low-pass Π-filter.
[6] A Π-filter results in a much lower ripple factor than a capacitor or choke input filter alone.
It may be followed by additional LC or RC filter sections to further reduce ripple to a level tolerable by the load.
[7] Switched-mode power supplies usually include a voltage regulator as part of the circuit.
Ripple is undesirable in many electronic applications for a variety of reasons: Ripple current is a periodic non-sinusoidal waveform derived from an AC power source characterized by high amplitude narrow bandwidth pulses.
Ripple current results in increased dissipation in parasitic resistive portions of circuits like ESR of capacitors, DCR of transformers and inductors, internal resistance of storage batteries.
The ripple of these networks, unlike regular filters, will never reach 0 dB at minimum loss if designed for optimum transmission across the passband as a whole.
On the other hand, the ripple can be reduced by increasing the order of the filter while at the same time maintaining the same rate of roll-off.
