Half-Wave Rectifiers


As long as the input voltage of the circuit shown below is larger than the diode's threshold voltage, the half-wave rectifier behaves as described next. Only the positive half-cycles of the ac input voltage appear across the load, so that a pulsating dc voltage is output.

During the positive half-cycle: The diode D1 is forward-biased and conducts current to the load resistor. The voltage produced across the load by the current has the same shape as the positive half-cycle of the input voltage, as shown in the following animation.

During the negative half-cycle: The diode is reverse-biased. There is no voltage across the load, so the output voltage or resistor's voltage is 0 V.


The average (dc) value of the half-wave rectified output is determined by finding the area under the curve over a full cycle. Using calculus to ascertain this area under the half-cycle and then dividing by the period, the average output voltage can be calculated. Here, the diode barrier potential is not taken into account.


The expression for the peak voltage depends on the type of diode being used and its barrier potential, usually 0.7 volts for a silicon diode and 0.3 for a germanium one.


Maximum Reverse or peak inverse voltage:

The maximum value of reverse voltage, sometimes designated as peak inverse voltage (PIV) occurs at the peak of the negative alternation of the input cycle, when the diode is reverse-biased. The PIV equals the peak value of the input voltage and the diode must be capable of withstanding this amount of repetitive reverse voltage.

The PIV for the following circuit is illustrated; its value really depends on each circuit's configuration.




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