FULL WAVE RECTIFIERA.C TO D.C CONVERTERTHEORY

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 process is known as rectification .Rectifiers have many uses, but are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers. In gas heating systems flame rectification is used to detect presence of flame. The simple process of rectification produces a type of DC characterized by pulsating voltages and currents (although still unidirectional). Depending upon the type of end-use, this type of DC current may Then be further modified into the type of relatively constant voltage DC characteristically produced by such sources as batteries and solar cells. A diode bridge is an arrangement of four (or more) diodes in a bridge circuit configuration that provides the same polarity of output for either polarity of input. When used in its most common application, for conversion of an alternating current (AC) input into a direct current (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding.

CIRCUIT DIAGRAM

Construction:-The diodes labelled D1 to D2 are arranged in "seriespairs" with only two diodes conducting currentduring each half cycle. During the positive half cycle of the supply, diodes D1 and D4 conduct inseries while diodes D2 and D3 are reverse biasedand the current flows through the load as shownbelow.

Full Wave BridgeRectifier:-Half-wave rectification:-In half wave rectification of a single-phase supply, eitherthe positive or negative half of the AC wave is passed,while the other half is blocked. Because only one half of the input waveform reaches the output, mean voltage islower. Half-wave rectification requires a single diode in asingle-phase supply, or three in a three-phase supply.Rectifiers yield a unidirectional but pulsating directcurrent; half-wave rectifiers produce far more ripple thanfull-wave rectifiers, and much more filtering is needed toeliminate harmonics of the AC frequency from the output.

Full-wave rectification:-A full-wave rectifier converts the whole of the input wave form to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and yields a higher mean output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed. Single semiconductor diodes, double diodes with common cathode or common anode, and four-diode bridges, are manufactured as single components.

Bridge rectifier: A full-wave rectifier using 4 diodes.For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (cathode-to-cathode or anode-to-anode, depending upon output polarity required) can form a full-wave rectifier. Twice as many turns are required on the transformer secondary to obtain the same output voltage than for a bridge rectifier, but the power rating is unchanged.

 Rectifier output smoothing:-

While half-wave and full-wave rectification can deliverunidirectional current, neither produces a constantvoltage. In order to produce steady DC from a rectified ACsupply, a smoothing circuit orfilteris required. In itssimplest form this can be just areservoir capacitororsmoothing capacitor, placed at the DC output of therectifier. There will still be an ACripplevoltagecomponent at the power supply frequency for a half-waverectifier, twice that for full-wave, wher the voltage is notcompletely smoothed.