# Half Wave Rectifier Principle

Half Wave Rectifier :

Half-Wave Rectifier Operation

The below Figure illustrates the process called half-wave rectification. A diode is connected toÂ an ac source and to a load resistor, RL, forming a half-wave rectifier. Keep in mind thatÂ all ground symbols represent the same point electrically. Letâ€™s examine what happens during one cycle of the input voltage using the ideal model for the diode. When the sinusoidalÂ input voltage (Vin) goes positive, the diode is forward-biased and conducts current throughÂ the load resistor, as shown in part (a). The current produces an output voltage across theÂ load RL, which has the same shape as the positive half-cycle of the input voltage.

(a) During the positive alternation of the ACÂ input voltage, the output voltage looks like the positiveÂ half of the input voltage. The current path is through ground back to the source.

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(b) During the negative alternation of the input voltage, the current is 0, so the output voltage is also 0.

When the input voltage goes negative during the second half of its cycle, the diode isÂ reverse-biased. There is no current, so the voltage across the load resistor is 0 V, as shownÂ in Figure (b). The net result is that only the positive half-cycles of the ac input voltageÂ appear across the load. Since the output does not change polarity, it is a pulsating dc voltage output as shown in above figure.

Average Value of the Half-Wave Output Voltage

The average value of the half-waveÂ rectified output voltage is the value you would measure on a dc voltmeter. Mathematically, it isÂ determined by finding the area under the curve over a full cycle, as illustrated in Below Figure,Â and then dividing by 2p, the number of radians in a full cycle. The result of this is expressedÂ in below Equation , where Vp is the peak value of the voltage. This equation shows that VAVG is

Effect of the Barrier Potential on the Half-Wave Rectifier Output

When the practical diode modelÂ is used with the barrier potential of 0.7 V taken into account, this is what happens. DuringÂ the positive half-cycle, the input voltage must overcome the barrier potential before theÂ diode becomes forward-biased. This results in a half-wave output with a peak value that isÂ 0.7 V less than the peak value of the input. The expression for theÂ peak output voltage is

Peak Inverse Voltage (PIV)

The peak inverse voltage (PIV) equals the peak value of the input voltage, and the diodeÂ must be capable of withstanding this amount of repetitive reverse voltage. For the diode,Â the maximum value of reverse voltage, designated as PIV, occurs at the peakÂ of each negative alternation of the input voltage when the diode is reverse-biased. A diodeÂ should be rated at least 20% higher than the PIV.