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What are Rectifiers?

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RECTIFIER CIRCUIT:-
Since a diode has the characteristic of having a much greater conductivity in one direction than in the other, it will produce a direct component of current when connected in series with an alternating voltage and a load. This process is known as rectification and is the main use to which diodes are put. There are numerous applications for rectification, e.g. driving a d.c. motor from a.c. mains and the production of direct-voltage supplies for electronic amplifiers.

HALF WAVE RECTIFIER:-
While alternating currents and voltages play the leading roles in most electrical and electronic equipment, nevertheless many devices can either only operate on unidirectional currents and voltages, or at least they require such a supply as part of their mode of operation. The process of obtaining unidirectional currents and voltages from alternating currents and voltages is termed  rectification. When the applied voltage acts in the forward direction, there is no voltage drop across the diode and a current flows unimpeded. However, when the applied voltage acts in the reverse direction, a voltage drop appears across the diode and no current flows.

The current can only flow through the diode in one direction and thus the load current can only flow during alternate half-cycles. For this reason, the system is known as half-wave rectification. The load current, and hence the voltage drop across the load, is unidirectional and could be described as direct, although this term is more usually reserved for steady unidirectional quantities.
FULL WAVE RECTIFIER:-
The half-wave rectifier gave rise to an output which had a unidirectional current, but the resulting current does not compare favourably with thedirect current that one would expect from, say, a battery. One reason is thatthe half-wave rectifier is not making use of the other half of the supply wave-form. It would be technically and economically advantageous if both halveswere rectified and this may be achieved by a full-wave rectifier network. Here C is a centre tap on the secondary of the transformer, thus the e.m.f.s induced in each section of the secondary are equal, and when the potential of A is positive with respect to C, so is that of C positive with respect to B. Withthese polarities, diode D1will conduct while diode D2is non-conducting.When these polarities reverse, diode D2will conduct and D1will be non-conducting. In this way each diode conducts on alternate half-cycles, passing current through the load in the same direction.
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