Thursday , October 18 2018

Half Wave Rectifier AC/DC Converter

Half Wave Rectifier

A fundamental application of the diode is the rectifier. The process of removing one-half the input signal to establish a DC level is called half wave rectification. A diode connected to an AC source and to a load resistor forms a half wave rectifier. The below given figure illustrates the process of half-wave rectification.

Half wave rectifier

Let’s examine what happens during one cycle of the input voltage using the ideal model for the diode. When the sinusoidal input voltage (Vin) goes positive, the diode is forward-biased and conducts current through the load resistor. The current produces an output voltage across the load R, which has the same shape as the positive half-cycle of the input voltage. When the input voltage goes negative during the second half of its cycle, the diode is reverse-biased. There is no current, so the voltage across the load resistor is 0 V. The net result is that only the positive half-cycle of the AC input voltage appear across the load. Since the output does not change polarity, it is a pulsating DC voltage with a frequency of 50 Hz.

Average Value of Half Wave Rectifier Output Voltage

The average value of the half wave rectified output voltage is the value measurable on a DC voltmeter. It is determined by finding the area under the curve over a full cycle and then dividing by 2π (Number of radians in a full cycle). The result of this is expressed as below:

VAVG = Vp

where Vp is the peak value of the voltage. This equation shows that VAVG is approx. 31.8% of Vp for a half wave rectified voltage.

Effect Of Barrier Potential On Half Wave Rectifier Output

When the practical diode model is used with the barrier potential of 0.7 V taken into account. During the positive half-cycle the input voltage must overcome the barrier potential before the diode becomes forward-biased. This results in a half-wave output with a peak value that is 0.7 V less than the peak value of the input. The expression for the peak output in practical scenario is:

Vp =  Vp(in) – 0.7 V

It is usually acceptable to use the ideal diode model, which neglects the effect of the barrier potential, when the peak value of the applied voltage is much greater than the barrier potential.

Peak Inverse Voltage (PIV)

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

PIV = Vp(in) 

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