Lecture # 12&13 SWITCHING-MODE POWER SUPPLIES

1. Lecture # 12&13SWITCHING-MODE POWER SUPPLIES

2. Switching-Mode Power Supplies

3. Introduction to Switching Regulators Objective of topic is to answer the following questions: What is a switching power supply? What types of switchers are available? Why is a switcher needed? How does a switcher operate in general? How does a buck converter operate? How does a boost converter operate? How does a buck-boost converter operate? How many design topologies of a switching power supplies?

4. Introduction to Switching Regulators Intended Audience: Electrical engineers with limited power supply background A simple, functional understanding of inductors and capacitors is assumed A simple, functional understanding of transistors is assumed Expected Time: Approximately 120 minutes

5. Outline of the presentation Switching Regulator Overview What is a Switching Regulator? Why is a switcher needed? What are the main differences between a switching and linear regulator? Buck, Boost, Buck-Boost (Inverting) Five designing topologies.. Flyback converter. Forward converter. Push-pull converter. Half Bridge converter. Full-Bridge converter. 3. Switching Regulator Operation . How does a Switching Regulator works? Switching Regulators components. • Switching mode DC power supplies

6. What is Switching Power Supply?

7. What is Switching Power Supply? • The advantage of a switching-mode power supply is that the relatively high frequency oscillator allows the use of small, lightweight and low-cost transformers. • This makes them considerably smaller and lighter than linear power supplies. Almost all modern powers supplies, including those in PCs, are switching mode power supplies. Their disadvantages are complexity and RF egress (interference).

8. What is a Switching Regulator? Converts an input voltage into desire output voltage. The power transistor operates as a switch, completely on or off. An energy storage part (inductor) is used in the architecture Switching Regulator

9. Choosing Between Linear and Switching Regulators When possible, most designers would prefer to use a linear voltage regulator rather than a switching voltage regulator Linear regulators are usually lower in price Linear regulators are usually simpler to implement Linear regulators do not have associated noise/ripple problems apparent in switching regulators

10. Choosing Between Linear and Switching Regulators When to use a switching regulator : When the minimum input voltage is at or below the desired output voltage Linear regulators cannot provide an output voltage greater than the input voltage VIN < VOUT

11. Choosing Between Linear and Switching Regulators When to use a switching regulator: The efficiency of a linear regulator cannot maintain the junction temperature below the specified maximum The maximum junction temperature is usually 150C The efficiency of linear regulators often prohibit their use in high voltage, high current applications

12. Why are switching regulators needed? The power dissipation is too high for a linear regulator The efficiency of a linear regulator cannot maintain the junction temperature below maximum (150 °C) The heat sinking of a linear regulator is prohibitive in price or space OutputPower Switching Regulator Linear Regulator Maximum Power Dissipation Linear Regulator

13. Why are switching regulators needed? The desired output voltage is greater than the input voltage Linear regulators cannot provide an output voltage greater than the input voltage The desired output voltage is opposite polarity than the input voltage Linear regulators cannot invert an input voltage Power Supply 1.5 V Battery 5 V Required Power Supply 12 V Battery -12 V Required

14. Types of Switching Regulators AC-DC, AC-AC, DC-AC, and DC-DC Converters DC-DC AC-AC DC-AC AC-DC 110 Vac 110 Vac 12 Vdc 12 Vdc t t t t 220 Vac 110 Vac 12 Vdc 5 Vdc t t t t

15. Types of DC-DC Converters Step Down, Step Up and Inverting V V Vin = 12 V Step Down Buck Vout = 5 V t t V V Vout = 12 V Step Up Boost Vin = 5 V t t V V Inverting Buck-Boost Vin = 5V t Vout = -10 V t

16. Basic Circuit Configuration Buck VIN > VOUT Boost VIN < VOUT Buck-Boost VIN < -VOUT < VIN VIN VIN VIN ISW ISW VGATE VGATE IL IL L VOUT VOUT VOUT VM L VM VM C C VGATE C IL ISW L • All topologies consists of the same basic components but are arranged differently

17. Buck Configuration The input voltage is always greater than the output voltage VIN VOUT VIN ISW 20V 10V VGATE 7.5V 15V IL VOUT 5V 10V L VM 2.5V 5V C 0V 0V time time

18. Boost Configuration The input voltage is always less than the output voltage VIN VOUT VIN 24V 20V 20V IL L 15V 15V VOUT 10V 10V VM C VGATE 5V 5V ISW 0V 0V time time

19. Buck-Boost Configuration The input voltage is always not constrained by the output voltage VIN VOUT VIN time 0V ISW 20V VGATE VOUT 15V -5V VM -10V 10V C IL L -15V 5V -20V 0V time

20. Switched-Mode DC Power Supplies • Five Designing Topologies. • Flyback converter. • Forward converter. • Push-pull converter. • Half Bridge converter. • Full-Bridge converter. • Operate at high frequencies • Easy to filter out harmonics

21. Flyback Converter

22. Mode 1 Operation -- Q1 ON • Current builds up in the primary winding • Secondary winding has the opposite polarity D1 OFF • C maintains the output voltage, supplies load current

23. Mode 2 Operation -- Q1 turned OFF • Polarity of the windings reverses • Diode D1 conducts, charging C and providing current to the load RL • Secondary current falls to 0 before the next cycle begins

24. Waveform Summary

25. Double-ended Flyback Converter

26. Forward Converter

27. Features • Includes a “reset” winding to return energy. • Secondary “dot” so that D2 forward biased when Q1 is ON – no energy stored in the primary. • Operates in continuous mode.

28. Mode 1 Operation -- Q1 ON • Current builds up in the primary winding • Energy transferred to the load

29. Mode 2 Operation -- Q1 turned OFF • Polarity of transformer voltages reverses • D2 turns OFF, D1 and D3 turn ON

30. Waveform Summary Vo D3

31. Double-ended Forward Converter

32. Push-Pull Converter

33. Push-Pull Operation • Q1 ON, Vs across the lower primary winding • Q2 ON, Vs across the upper primary winding

34. Half-Bridge Converter

35. Mode 1 Operation • Q1 ON, D1 conducting • Energy transferred to the load

36. Mode 2 Operation • Both transistors are OFF • D1 continues to conduct due to current in L1

37. Mode 3 Operation • Q2 ON, D2 conducting • Energy transferred to the load

38. Mode 4 Operation • Both transistors OFF • D2 continues to conduct due to current in L1

39. Full-Bridge Converter

40. Mode 1 Operation • Q1,Q4 ON, Q2,Q3 OFF • D1 conducting, energy transferred to the load

41. Mode 2 Operation • All transistors are OFF • D1 continues to conduct due to current in L1

42. Mode 3 Operation • Q2,Q3 are ON, Q1,Q4 OFF • D2 conducting, energy transferred to the load

43. Mode 4 Operation • All transistors are OFF • D2 continues to conduct due to current in L1

44. How a Switching Regulator Works VIN VOUT Switching Regulator 5V Filter Network Voltage OK time 50% Output Monitor VOUT Duty Cycle Controller

45. How a Switching Regulator Works VIN VOUT Voltage Regulator 5V Filter Network Voltage OK time 50% Output Monitor VOUT Duty Cycle Controller

46. How a Switching Regulator Works VIN VOUT Voltage Regulator 5V Filter Network Voltage OK time 50% Output Monitor VOUT Duty Cycle Controller

47. How a Switching Regulator Works VIN – 1V VOUT Voltage Regulator 5V Filter Network Voltage Low time 60% Output Monitor VOUT Duty Cycle Controller

48. How a Switching Regulator Works VIN – 1V VOUT Voltage Regulator 5V Filter Network Voltage Low time 60% Output Monitor VOUT Duty Cycle Controller

49. How a Switching Regulator Works VIN VOUT Switching Regulator 5V Filter Network Voltage Ok time 50% Output Monitor VOUT Duty Cycle Controller

50. Switching Regulator Components