Mon November 26, 2012 By: Hardik Chauhan

explain me filter circuit? how does it work? and explain how zener diode act as voltage regulator ?

Expert Reply
Mon November 26, 2012

The property of a p-n diode to conduct in one direction only can be used to rectify AC voltage, that is, restrict variations to one direction only.
Two simple rectifiers are (1) Half-wave and (2) Full-wave rectifiers.
(1) Half-wave rectifier: The circuit is as follows:
We can consider for simplicity, an ideal diode, whose reverse bias resistance is infinite. The AC source is the secondary of a transformer, which supplies voltage across A and B. When the voltage at S1 is positive, the diode is forward biased, and conducts.
When S1is negative, it is reverse biased, and does not conduct. So, we get an output across the load resistance only for positive half cycles. Since the negative half-cycles are suppressed, this circuit is called a half-wave rectifier.
(2) Full-wave rectifier: This circuit uses two diodes, and a center-tap transformer, whose secondary is wound into two equal parts. The voltages at any instant at S1 and S2 are out of phase with respect to each other. If the voltage at any instant at S1 is positive, diode conducts and since voltage at S2 is negative, does not conduct.

So, during this positive half-cycle, we get an output current and hence voltage across load resistance, as shown above.
If voltage at S1 becomes negative, only conducts, and we get an output in the negative half-cycle as well, which is however identical to the output in the positive half-cycle.

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