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# Fundamentals of DC Power Supplies

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Learn the fundamentals of DC power supplies. How they work and learn the basics of HWR, FWR and BR using simple concepts.
This slideshow is based on the textbook 'APPLIED ELECTRONICS' written by Vidyasagar Sir.

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### Fundamentals of DC Power Supplies

1. 1. Rectifiers (HWR, FWR & BR) Filter Circuits (Series & Shunt) Regulators (Zener & Transistor) 3-Terminal Voltage Regulators Switch Mode Power Supply
2. 2. Vp  Rectifier Circuits (HWR) It is a low quality rectifier circuit. It rectifies only one half cycle of AC. Its output voltage is equal to Vp/. The PIV of the diode is greater than Vp. Its ripple frequency is equal to frequency of AC voltage. The current through the diode is equal to load current. 27.02.2009 Designed by: D.S.Vidyasagar
3. 3. Rectifier Circuits (FWR) It is a good quality rectifier circuit. It rectifies both half cycles of AC. Its output voltage is equal to 2Vp/. The PIV of diode is greater than 2Vp. Its ripple frequency is double than the frequency of AC voltage. The current through each diode is half of the total load current. 27.02.2009 Designed by: D.S.Vidyasagar
4. 4. Rectifier Circuits (BR) It is a best quality rectifier circuit. It rectifies both half cycles of AC. Its output voltage is equal to 2Vp/. The PIV of the diode is greater than Vp. Its ripple frequency is double than the frequency of AC voltage. The current through each diode is equal to the total load current. 27.02.2009 Designed by: D.S.Vidyasagar
5. 5. Filter Circuits (Basics) The ripple means variations in impure DC voltage. Due to ripples the quality of DC voltage is reduced. Thus, the ripple factor is defined as the ratio of r.m.s. value of AC voltage to DC voltage. The ripple factor is independent of RL. 27.02.2009 Designed by: D.S.Vidyasagar
6. 6. Filter Circuits (Basics-2) The inductor can also store electricity in The capacitor can store electricity in the form of of across it. the form PDPD across it, for a short time. InIn capacitor currentlags voltage by 90. inductor current leads voltage by 90 . It charges upallows DCand discharges up to 63.28% current and The inductor to 36.72% in time T=RxC. produces high opposition (XL) to AC. It allows AC current with opposition (Xc) Thus,blocks DC.steady current but but it allows opposes changing current. 27.02.2009 Designed by: D.S.Vidyasagar
7. 7. Capacitor Filter Circuit When filter circuit is used load must be connected across the output. When first half cycle arrives, the capacitor charges up to Vp. When rectifier voltage drops, it gives out its stored energy to the load. Thus, it maintains constant voltage. Its filtration decreases as RL decreases. 27.02.2009 Designed by: D.S.Vidyasagar
8. 8. Inductor Filter Circuit When filter circuit is used load must be connected across the output. When first half cycle arrives, the current through inductor increases. When voltage of first half cycle drops counter current opposes this change. Thus, inductor produces opposition to changing current and allows pure DC only. Its filtration increases as RL decreases. 27.02.2009 Designed by: D.S.Vidyasagar
9. 9. Voltage Regulators A load means anything which we connect across the output of a circuit. When load is connected, loading effect is produced. Due to loading effect, the output voltage drops. This loaded voltage is called apparent voltage. The apparent voltage is always less than true voltage. 27.02.2009 Designed by: D.S.Vidyasagar
10. 10. Voltage Regulators Load regulation is defined as the change in output voltage when load current changes from minimum to maximum. Line regulation is defined as change in output voltage for a specified range of line voltage. 27.02.2009 Designed by: D.S.Vidyasagar
11. 11. Voltage Regulators Voltage regulator has two important facilities – It has over voltage protection i.e. when line voltage is abnormal it is switched off. It has over load protection i.e. when load current exceeds the limit, it is switched off. 27.02.2009 Designed by: D.S.Vidyasagar
12. 12. Zener Regulators The zener diode is a special PN junction diode. Its doping concentration decides the zener voltage. When a  +ve, k  –ve, its forward voltage is 0.7V. It cannot be used in rectification, since it conducts in both directions. When load resistor is disconnected from the circuit, total current flows through it. 27.02.2009 Designed by: D.S.Vidyasagar
13. 13. Shunt Zener Regulator The circuit stabilizes the output voltage, when RL = constant, as follows – When Vin  Is  Iz  but IL= constant So (Vin – Vz) and Vz = Vo = constant When Vin  Is  Iz  but IL= constant So (Vin – Vz)  and Vz = Vo = constant 27.02.2009 Designed by: D.S.Vidyasagar
14. 14. IS = IZ + IL constant
15. 15. IS = IZ + IL constant
16. 16. Shunt Zener Regulator The circuit stabilizes the output voltage when Vin = constant, as follows – When RL IL but Is = constant So Iz  and keeps Vo = constant When RL IL  but Is = constant So Iz  and keeps Vo = constant 27.02.2009 Designed by: D.S.Vidyasagar
17. 17. constant IS = IZ + IL constant
18. 18. constant IS = IZ + IL constant
19. 19. +ve +ve In any other Forward biased condition it is reversed biased –ve
20. 20. Ic Ie = Ic + Ib Ib Ic =  x Ib Ie
21. 21. Ic Ie = Ic + Ib Ib Ic =  x Ib Ie
22. 22. Ie = Ic + Ib Ib Ic =  x Ib
23. 23. Vb Vc
24. 24. Vb Vc
25. 25. constant
26. 26. constant
27. 27. 0.6V FB Vo = 0
28. 28. Pin-1 unregulated input Pin-2 regulated output Pin-3 ground pin
29. 29. Vo = Vin – Vce constant
30. 30. Vo = Vin – Vce constant
31. 31. 175
32. 32. LM 340–12 15V 12V
33. 33. 15V 12V LM 340–05
34. 34. Switch Mode Power Supply It is a sophisticated power supply. It produces very pure DC voltage. It has a square wave generator circuit. Its operating frequency is 20kHz. During +ve half cycle of square wave, the transistor conducts. During –ve half cycle, it is cut-off. 27.02.2009 Designed by: D.S.Vidyasagar
35. 35. Switch Mode Power Supply Its operating frequency is very high, generally 20kHz. So the valleys at output have small width. This width can be easily filled up using small filter capacitor. Its output voltage Vo = D x Vin 27.02.2009 Designed by: D.S.Vidyasagar
36. 36. Advantages of SMPS The transistor dissipates very little power in it. So output is proportional to input. It has high efficiency output. It has high current output. Hence, loading effects are negligible. Due to high frequency, ripples are less. 27.02.2009 Designed by: D.S.Vidyasagar
37. 37. 22.12.2013 Designed by: Prof. D.S.Vidyasagar