Mastering Power Supplies: Diode Applications in Rectifier Circuit

Are you ready to build your first power supply? 🛠️This lecture, presented by Dr. G. S. Virdi (Ex. Chief Scientist at CSIR-CEERI), dives deep into the Application of Diodes—the most fundamental analog device—in modern power electronics.You will gain a solid, quantitative understanding of how the p-n junction diode acts as the heart of a Rectifier Circuit, which is essential for converting AC mains voltage into usable DC voltage for all electronic devices.What You Will Learn:The Power Supply Block Diagram: Understand the function of each stage: Transformer, Rectifier, Filter, and Regulator.Half-Wave Rectifier (HWR): Master the operation, circuit analysis, and performance limitations (low $\eta$, high $r$).Full-Wave Rectifiers (FWR): Compare and contrast the two major types:Center-Tap Rectifier: Learn its high efficiency and cost implications.Bridge Rectifier: Discover why it is the most popular choice for modern design, its PIV advantage, and its trade-offs.Performance Metrics: Critically analyze and calculate key parameters like:Rectifier Efficiency ($\eta$): Up to $40.6\%$ (HWR) vs. $81.2\%$ (FWR).Ripple Factor ($r$): The measure of AC contamination in the DC output.Peak Inverse Voltage (PIV): The critical diode breakdown voltage consideration.This presentation is a must-view for all Electrical, Electronics, and Instrumentation Engineering students looking to build a strong foundation in Analog Circuit Design and Power Electronics.

1. Application of Diodes Dr.G.S.Virdi Ex.Chief Scientist CSIR -Central Electronics Engineering Research Institute Pilani -333031,India 1

2. Contents Design of Rectifier Circuits. Half Wave Rectification Full Wave Rectifier Filter Ripple Voltage and Diode Current Dr.G.S.Virdi 2

3. Rectifiers 3

4. Block diagram of Power Supply Dr.G.S.Virdi 4

5. Rectifier A circuit that converts ac voltage of main supply into pulsating dc voltage using one or more pn junction diodes. Half Wave Rectifier Full Wave Rectifier Center Tap Rectifier Bridge Rectifier Dr.G.S.Virdi 5

6. Half Wave Rectifier Circuit Diagram Dr.G.S.Virdi 6

7. Operation of Half Wave Rectifier Dr.G.S.Virdi 7

8. Waveform of Half Wave Rectifier Dr.G.S.Virdi 8

9. Average DC load Current (I DC ) Dr.G.S.Virdi 9

10. Average DC voltage (Edc) Dr.G.S.Virdi 10

11. RMS Load Current (Irms) RMS Load Voltage (Erms) Dr.G.S.Virdi 11

12. DC Power Delivered to the load Dr.G.S.Virdi 12

13. AC input power from transformer secondary Dr.G.S.Virdi 13

14. How effectively a rectifier converts ac into dc: Rectifier Efficiency (η) Ripple Factor (r) Dr.G.S.Virdi 14

15. Rectifier Efficiency (η) Tells us the percentage of total input ac power that is converted into useful dc output power. η = 40.6 % Under best conditions (no diode loss) only 40.6% of the ac input power is converted into dc power. The rest remains as the ac power in the load Dr.G.S.Virdi 15

16. Ripple Factor Measure of purity of the dc output of a rectifier Defined as the ratio of ac component of the output wave to the dc component in the wave Dr.G.S.Virdi 16

17. Ripple Factor This indicates that the ripple content in the output are 1.211 times the dc component. i.e. 121.1 % of dc component. The ripple factor is very high. Therefore a half wave rectifier is a poor converter of ac to dc. The ripple factor is minimized using filter circuits along with the rectifier. Dr.G.S.Virdi 17

18. Peak Inverse Voltage (PIV) PIV = Em Diode must be selected based on the PIV rating and the circuit specification. Dr.G.S.Virdi 18

19. Disadvantage of HWR The ripple factor of half wave rectifier is 1.21, which is quite high. The output contains lot of ripples The maximum theoretical efficiency is 40%. The practical value will be quite less than this. This indicates that HWR is quite inefficient. Dr.G.S.Virdi 19

20. Half WaveRectifier Center Tap Rectifier Dr.G.S.Virdi 20

21. Working of Center Tap Rectifier Current Flow during the positive half of the input cycle Current Flow during the negative half of the input cycle Dr.G.S.Virdi 21

22. Waveforms Dr.G.S.Virdi 22

23. Average DC current Average (DC) Voltage Dr.G.S.Virdi 23

24. RMS Load Current (Irms) RMS Load Voltage Dr.G.S.Virdi 24

25. DC Output Power AC input power (Pac) Dr.G.S.Virdi 25

26. Rectifier Efficiency (η) Dr.G.S.Virdi 26

27. Ripple Factor This indicates that the ripple contents in the output are 48% of the dc component which is much less than that for the half wave rectifier. Dr.G.S.Virdi 27

28. Peak Inverse Voltage Dr.G.S.Virdi 28

29. Advantages of Full Wave Rectifier Efficiency is higher. The large dc power output The ripple factor is less Disadvantages of Full Wave Rectifier PIV rating of diode is higher. Higher PIV diodes are larger in size and costlier. The cost of center tap transformer is high. Dr.G.S.Virdi 29

30. Bridge Rectifier Dr.G.S.Virdi 30

31. Working of Bridge Rectifier Dr.G.S.Virdi 31

32. Waveforms of Bridge Rectifier Dr.G.S.Virdi 32

33. Parameters : Dr.G.S.Virdi 33

34. Advantages of Bridge Rectifier It does not need center tap transformer secondary. The transformer secondary voltage of CT rectifier is 2Vm, where as in Bridge the transformer secondary must have a peak voltage of Vm. That is the transformer secondary of CT rectifier must have double the number of turns. Such transformers are costlier. If stepping up or stepping down of voltage is not needed, we may even do away without transformer. Each diode in center tap has a PIV rating of 2Vm, whereas diodes in bridge rectifier needs a PIV rating of Vm. Hence the diodes for use in center tap rectifier are costlier than meant for bridge rectifier. Dr.G.S.Virdi 34

35. Disadvantages of Bridge Rectifier It requires four diodes, two of which conduct in alternate half cycles. This creates a total voltage drop of 1.4V (if Si diodes are used). Therefore this creates a problem if low dc voltage is required. The secondary voltage is low and two diode voltage drop of 1.4V becomes significant. Dr.G.S.Virdi 35

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