How does a rectifier convert AC into DC and what happens to the frequency while the voltage is converted into DC?

Answer 1

An AC electric supply has its voltage continously varying in a sinusoidal pattern at a fixed frequency of 50Hz ( i.e 50 sine waves per sec.) in countries following the British system & 60Hz for the American system.

The voltage variation over a single cycle increases from zero to a certain positive maximum voltage & then reduces to zero & follows the same pattern for the negative cycle where the voltage is negative with respect to a reference measurement point. This repeats continously.

This AC supply is advantageous for practical reasons of the voltage being easily stepped down ( or up ) with Transformers as per the needs of consumers. Also certain AC motors have a very high mechanical conversion efficiency.

However there are certain applications where a DC supply ( akin to a continous fixed voltage from a battery ) is required e.g electroplating , DC traction motors which have a very high inherent starting torque. The DC voltage as per requirements is ideally fixed at a certain level ( it can be called a positive or negative voltage , which is essentially determined by the point of reference used for the measurement . The frequency of DC supply is essential zero. DC devices cannot be plugged directly into an AC supply & therefore a Rectifier unit which consists of one ( for very low power application ) or more Electronic Diodes in particular combinations which GATE the AC supply to prevent the voltage excursions of the opposite polarity from reaching the DC device. This rectification gives a DC supply which has some variations called ripple & is not an ideal DC. Depending on the application other components like capacitors or more sophisticated active electronic circuits are used to remove these ripples and improve the DC supply. Most DC devices have supply polarities to be observed i.e

the device may not work or get damaged if the DC supply polarity is reversed.

It may be noted that almost all electronic circuits work with DC supply , even though outwardly the user may be plugging the device in to an AC supply.

If there is a degradation in the DC improvement circuit it will be noticiable as a hum in audio amplifiers or a waving picture on the TV screen in older systems.

In modern devices use of special switching power supplies has made it possible to get almost ideal DC.