A capacitor-input filter is a filter circuit in which the first element is a

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

connected in parallel with the output of the rectifier in a linear

power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a ...

. The capacitor increases the DC voltage and decreases the

ripple Ripple may refer to: Science and technology * Capillary wave, commonly known as ripple, a wave traveling along the phase boundary of a fluid ** Ripple, more generally a disturbance, for example of spacetime in gravitational waves * Ripple (electri ...

voltage components of the output. The capacitor is often referred to as a

smoothing capacitor A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an inver ...

or reservoir capacitor. The capacitor is often followed by other alternating series and parallel filter elements to further reduce ripple voltage, or adjust DC output voltage. It may also be followed by a

voltage regulator A voltage regulator is a system designed to automatically maintain a constant voltage. A voltage regulator may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism, or electronic components ...

which virtually eliminates any remaining ripple voltage, and adjusts the DC voltage output very precisely to match the DC voltage required by the circuit.

Operation

While during the time the rectifier is conducting and the potential is higher than the charge across the capacitor, the capacitor will store energy from the transformer; when the output of the rectifier falls below the charge on the capacitor, the capacitor will discharge energy into the circuit. Since the rectifier conducts current only in the forward direction, any energy discharged by the capacitor will flow into the load. This results in output of a DC voltage upon which is superimposed a waveform referred to as a sawtooth wave. The sawtooth wave is a convenient linear approximation to the actual waveform, which is exponential for both charge and discharge. The crests of the sawtooth waves will be more rounded when the DC resistance of the transformer secondary is higher.

Ripple current

A ripple current which is 90 degrees out of phase with the ripple voltage also passes through the capacitor.

References

{{DEFAULTSORT:Capacitor-Input Filter Linear filters Analog circuits Electronic filter topology

Operation

Ripple current

See also

References