Half wave rectifier Definition
The half wave rectifier circuit is constructed simply by connecting a diode between the power supply transformer and the load, as shown in Figure (a). When the secondary ac voltage swings positive, as shown in Figure (b), the anode of the diode is made positive, causing the diode to turn ON and connect the positive half-cycle of the secondary ac voltage across the load (RL). When the secondary ac voltage swings negative, as shown in Figure (c), the anode of the diode is made negative, and therefore the diode will turn OFF. This will prevent any circuit current, and no voltage will be developed across the load (RL).Half wave rectifier vutput voltage Formula
Figure (d) illustrates the input and output waveforms for the half wave rectifier circuit. The 120 V ac rms input, or 169.7 V ac peak input, is applied to the 17:1 step-down transformer, which produces an output of:
Because the diode will only connect the positive half-cycle of this ac input across the load (Rl), the output voltage (VRL) is a positive pulsating dc waveform of 10 V peak. In this final waveform in Figure (d), you can see that the circuit is called a half wave rectifier because only half of the input wave is connected across the output.
The average value of two half-cycles is equal to 0.637 V peak. Therefore, the average value of one half-cycle is equal to 0.318 V peak voltage of (0.637/2 = 0.318):
Vavg =0.318 x Vs peak
In the example in Figure , the average voltage of the half-wave output will be:
Vavg = 0.318 X Vs peak
Vavg = 0.318 X 10 V
Vavg = 3.18 V
To be more accurate, there will, of course, be a small voltage drop across the diode due to its barrier voltage of 0.7 V for silicon and 0.3 V for germanium. The output from the circuit in Figure 1 would actually have a peak of 9.3 V (10 V - 0.7 V), and therefore an average of 2.96 V (0.318 X 9.3 V), as shown in Figure (e).
Vout =Vs - Vdiode
Half wave rectifier Graph
Another point to consider is the reverse breakdown voltage of the junction or rectifier diode. When the input swings negative, as illustrated in Figure (c), the entire negative supply voltage will appear across the open or OFF diode. The maximum reverse breakdown voltage, or peak inverse voltage (PIV) rating of the rectifier diode, must therefore be larger than the peak of the ac voltage at the diode’s input.
Output Polarity of Half wave rectifier
Output polarity. The half wave rectifier circuit can be arranged to produce either a positive pulsating dc output, as shown in Figure (a), or a negative pulsating dc output, as shown in Figure (b). Studying the difference between these circuits you can see that in Figure (a) the rectifier diode circuit is connected to conduct the positive half-cycles of the ac input, while in Figure (b) the rectifier diode is reversed so that it will conduct the negative half-cycles of the ac input By changing the direction of the diode in this manner, the rectification can be made to produce either a positive or a negative dc output
Ripple frequency of Half wave Rectifier
Referring to the input/output waveforms of the half wave rectifier circuit shown in Figure 11-20, you can see that one output ripple is produced for every complete cycle of the ac input. Consequently, if a half wave rectifiers is driven by the 120 V ac 60 Hz line voltage, each complete cycle of the ac input and each complete cycle of the output will last for one-sixtieth or 16.67 ms (1/60 = 16.67 ms). The frequency of the pulsating dc output from a rectifier is called the ripple frequency, and for half wave rectifier circuits, the:
output pulsating DC ripple frequency = AC frequency