Class a Commutation: lOAD Commutation

Class a Commutation: lOAD Commutation

BS Regular 18 March, 17 Rectifier Calculations Lecture 5 Electronic Fundamental

Muhammad Zahid Diode Model 2

Diode Model Determine the forward voltage and forward current for the diode in Figure 218(a) for each of the diode models. Also find the voltage across the limiting resistor in each case. Assume at the

determined value of forward current. Value of rd is 10 ohms. (b) Determine the reverse voltage and reverse current for the diode in Figure 218(b) for each of the diode models. Also find the voltage across the limiting 3

Diode Model 4 Solution

5 Solution 6

Solution 7 Half Wave

Rectifiers 8 Average Voltage The average value of the half-wave rectified output voltage is the value you

would measure on a dc voltmeter. Average voltage of half wave rectifier are: 9 Effect of Barrier Potential When the practical diode model is used with the barrier potential of

0.7 V taken into account, this is what happens. 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.

10 Transformer Coupling A transformer is often used to couple the ac input voltage from the source to the rectifier, as shown in Figure 227.

11 Transformer Coupling Transformer coupling provides two advantages. First, it allows the source voltage to be stepped down as needed.

Second, the ac source is electrically isolated from the rectifier, thus preventing a shock hazard in the secondary circuit. The secondary voltage of a transformer equals the turns ratio, n, times the primary voltage. 12

Transformer Coupling 13 Half Wave Rectifiers

14 Example 15

Solution 16 Peak Inverse Voltage

17 Example 18

Solution 19 Full Wave Rectifiers

20 Average Voltage A full-wave rectifier allows unidirectional (one-way) current through the load during the entire of the input cycle, whereas a half-wave rectifier allows current through the load only during one-half of the cycle.

The result of full-wave rectification is an output voltage with a frequency twice the input frequency and that pulsates every half-cycle of the input. Average voltage of full wave rectifier are: 21

Full Wave Rectifiers 22 Effect of Turn Ratio on Output

The output voltage of a center-tapped full-wave rectifier is always one-half of the total secondary voltage less the diode drop, no matter what the turns ratio. 23

Peak Inverse Voltage Each diode in the full-wave rectifier is alternately forward-biased and then reverse-biased. The maximum reverse voltage that each diode must withstand is the peak secondary voltage Vp(sec). The peak inverse voltage across either diode in a full-wave centertapped rectifier is

24 Full Wave Rectifiers 25

Solution 26 Bridge Rectifiers 27

Bridge Output Voltage Two diodes are always in series with the load resistor during both the positive and negative half-cycles. If these diode drops are taken into account, the output voltage is

28 Peak Inverse Voltage Since the output voltage is ideally equal to the secondary voltage If the diode drops of the forward-biased diodes are included, the peak

inverse voltage across each reverse-biased diode in terms of Vp(out) is 29 Relationship Between RMS and Peak Voltage

V p 2 Vrms 1.414Vrms Vrms Vp Vp

1.414 2 30

Full-wave Bridge Rectifiers 31 Solution

32 Assignment# 1 33

Question # 1 & 2 Q1. Determine the average value of the half-wave voltage if its peak amplitude is 12 V. Q2. Determine the peak output voltages for the rectifiers in Figure 224 if the peak input in part (a) is 3 V and the peak input in part (b) is 50 V.

34 Question # 3 35

Question # 4 & 5 Q4. Find the average value of the full-wave rectified voltage if its peak is 155 V. Q5. What diode PIV rating is required to handle a peak input of 160 V in figure below?

36 Question # 6 Q6. Determine the peak output voltage for the bridge rectifier in figure below if the transformer produces an rms secondary voltage of 30 V.

What is the PIV rating for the diodes? 37 Assignment Submission Date:

st 21 March, 2016 Must be submitted in a file / folder. 38

Thank You 39

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