1. Chapter 3 DC to DC Converters
Outline
3.1 Basic DC to DC converters
3.1.1 Buck converter (Step- down converter)
3.1.2 Boost converter (Step-up converter)
3.2 Composite DC/DC converters and connection of multiple DC/DC converters
3.2.1 A current-reversible chopper
3.2.2 Bridge chopper (H-bridge DC/DC converter)
3.2.3 Multi-phase multi-channel DC/DC converters

2. 3.1 Basic DC to DC converters
3.1.1Buck converter
SPDT switch changes dc component
Switch output voltage waveform
Duty cycle D: 0 ≤ D ≤ 1
complement D: D´ = 1 - D

3. Dc component of switch output voltage

4. Insertion of low- pass filter to remove switching harmonics and pass only dc component

5. Basic operation principle of buck converter

6. Thought process in analyzing basic DC/DC converters
1) Basic operation principle (qualitative analysis)
–How does current flows during different switching states
–How is energy transferred during different switching states
2) Verification of small ripple approximation
3) Derivation of inductor voltage waveform during different switching states
4) Quantitative analysis according to inductor volt-second balance or capacitor charge balance

7. Actual output voltage waveform of buck converter

8. Buck converter analysis: inductor current waveform

9. Inductor voltage and current subinterval 1: switch in position 1

10. Inductor voltage and current subinterval 2: switch in position 2

11. Inductor voltage and current waveforms

12. Determination of inductor current ripple magnitude

13. Inductor current waveform during start-up transient

14. The principle of inductor volt- second balance: Derivation
Inductor defining relation:
Integrate over one complete switching period:
In periodic steady state, the net changes in inductor current is zero:
Hence, the total area(or volt-seconds)under the inductor voltage waveform is zero whenever the converter operates in steady state.
An equivalent form:
The average inductor voltage is zero in steady state.

15. Inductor volt-second balance:Buck converter example
Integral of voltage waveform is area of rectangles:
average voltage is
Equate to zero and solve for V:

16. 3.1.2Boost converter
Boost converter example

17. Boost converter analysis

18. Subinterval 1: switch in position 1

19. Subinterval 2: switch in position 2

20. Inductor voltage and capacitor current waveforms

21. Inductor volt- second balance

22. Conversion ratio M(D) of the boost converter

23. Determination of inductor current dc component

24. Continuous- Conduction- Mode (CCM) and Discontinuous Conduction-Mode (DCM) of boost

25. 3.2 Composite DC/DC converters and connection of multiple DC/DC converters
3.2.1 A current reversible chopper

26. 3.2.2Bridge chopper (H-bridge chopper)

27. 3.2.3Multi-phase multi-channel DC/DC converter