1. DC-DC Switch-Mode Converters
Chapter 7
DC-DC Switch-Mode Converters
dc-dc converters for switch-mode dc power supplies and dc-motor drives
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

2. Block Diagram of DC-DC Converters
Functional block diagram
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

3. Stepping Down a DC Voltage
A simple approach that shows the evolution
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

4. Pulse-Width Modulation in DC-DC Converters
Role of PWM
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

5. Chapter 7 DC-DC Switch-Mode
Step-Down DC-DC Converter
Pulsating input to the low-pass filter
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

6. Step-Down DC-DC Converter: Waveforms
Steady state; inductor current flows continuously
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

7. Chapter 7 DC-DC Switch-Mode
Step-Down DC-DC Converter: Waveforms at the boundary of Cont./Discont. Conduction
Critical current below which inductor current becomes discontinuous
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

8. Step-Down DC-DC Converter: Discontinuous Conduction Mode
Steady state; inductor current discontinuous
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

9. Step-Down DC-DC Converter: Limits of Cont./Discont. Conduction
The duty-ratio of 0.5 has the highest value of the critical current
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

10. Step-Down DC-DC Converter: Limits of Cont./Discont. Conduction
Output voltage is kept constant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

11. Step-Down Conv.: Output Voltage Ripple
ESR is assumed to be zero
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

12. Step-Up DC-DC Converter
Output voltage must be greater than the input
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

13. Step-Up DC-DC Converter Waveforms
Continuous current conduction mode
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

14. Step-Up DC-DC Converter: Limits of Cont./Discont. Conduction
The output voltage is held constant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

15. Step-Up DC-DC Converter: Discont. Conduction
Occurs at light loads
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

16. Step-Up DC-DC Converter: Limits of Cont./Discont. Conduction
The output voltage is held constant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

17. Step-Up DC-DC Converter: Effect of Parasitics
The duty-ratio is generally limited before the parasitic effects become significant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

18. Step-Up DC-DC Converter Output Ripple
ESR is assumed to be zero
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

19. Step-Down/Up DC-DC Converter
The output voltage can be higher or lower than the input voltage
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

20. Step-Up DC-DC Converter: Waveforms
Continuation conduction mode
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

21. Step-Up DC-DC Converter: Limits of Cont./Discont. Conduction
The output voltage is held constant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

22. Step-Up DC-DC Converter: Discontinuous Conduction Mode
This occurs at light loads
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

23. Step-Up DC-DC Converter: Limits of Cont./Discont. Conduction
The output voltage is held constant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

24. Step-Up DC-DC Converter: Effect of Parasitics
The duty-ratio is limited to avoid these parasitic effects from becoming significant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

25. Step-Up DC-DC Converter: Output Voltage Ripple
ESR is assumed to be zero
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

26. Chapter 7 DC-DC Switch-Mode
Cuk DC-DC Converter
The output voltage can be higher or lower than the input voltage
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

27. Cuk DC-DC Converter: Waveforms
The capacitor voltage is assumed constant
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

28. Converter for DC-Motor Drives
Four quadrant operation is possible
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by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

29. Chapter 7 DC-DC Switch-Mode
Converter Waveforms
Bi-polar voltage switching
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

30. Chapter 7 DC-DC Switch-Mode
Converter Waveforms
Uni-polar voltage switching
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

31. Output Ripple in Converters for DC-Motor Drives
bi-polar and uni-polar voltage switching
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

32. Switch Utilization in DC-DC Converters
It varies significantly in various converters
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by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

33. Equivalent Circuits in DC-DC Converters
replacing inductors and capacitors by current and voltage sources, respectively
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters

34. Reversing the Power Flow in DC-DC Conv.
For power flow from right to left, the input current direction should also reverse
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 7 DC-DC Switch-Mode
Converters