DC-DC_Converters. pptx power electronics

Electronic communication

1. DC-DC CONVERTERS Dc-dc switch-mode converters Chapter 7 in ( Power Electronics by Mohan, Undeland , Robbins)

2. Learning Objectives: Describe the switching techniques for dc-dc conversion The types of dc-dc converters Operation of dc-dc converters Their performance parameters

3. Introduction DC-DC converter (chopper ) are needed, as many industrial applications are depended on DC voltage source. Application performance improves if DC source is variable. Control and variation of a constant dc voltage source is achieved with the help of a chopper. Chopper is basically a static power electronic device which converts fixed dc voltage to a variable DC voltage.

4. Chopper Block diagram Chopper can increase or decrease the DC voltage level at its output.

5. Response of L and C

6. Inductor Voltage and Current in Steady State

7. Capacitor Voltage and Current in Steady State

8. Typical dc-dc converter

9. Typical dc-dc converter

10. Control of DC-DC Converter

11. DC-DC Switch-mode conversion

12. Pulse-width modulation

13. Step-Down (Buck) Converters

14. Step-Down DC-DC Converter In practise electrical loads are inductive. Due to inductor effects it is important to add FWD. A low pass filter ( Cap & inductor) to diminish the output voltage fluctuation.

15. Step-Down DC-DC Converter

16. Operation:

17. Waveforms:

18. Operation:

19. Operation:

20. Output voltage ripple

21. Example: A step down chopper fed from a 12VDC source is used to drive a 5V load. The power delivered to the load is 250W with 5% p-p ripple in the output voltage. If the chopper operates at 25kHz. Sketch a neatly labelled diagram of the converter. Calculate the duty cycle. Calculate input current to the converter. Calculate Filter inductance required in the converter Calculate Average diode current Calculate the value of the capacitor. Plot fully labelled waveforms for {switch voltage, Inductor voltage, diode voltage, the capacitor voltage, inductor current}

22. Example solution

23. Example Continued:

24. Example Continued:

25. Example Continued:

26. Step-Up (Boost) Converter

27. Boost: Output voltage must be greater than the input Its main application is in regulated dc power supplies and the regenerative braking of dc motors.

28. Operation:

29. Continuous current conduction mode The output voltage tends to ∞ as D approaches 1

30. Boundary between Cont and Discont conduction

31. Inductor Waveforms:

32. Output voltage ripple:

33. Waveforms

34. Example Design a boost converter for 48VDC to 156VDC and supplies a 100W load at 75kHz. The ripple current in the inductor is equal to 5% p-p and the voltage ripple equal to 1% p-p. Assuming converter efficiency of 100%. Sketch a neatly labelled diagram of the boost converter assuming MOSFETs were used. Calculate duty cycle. Calculate Average input current. Calculate the value of the inductor. Average current of the diode. Value of the capacitor

35. Example solution:

36. Example solution:

37. Example solution:

38. Example solution:

39. Buck-Boost Converters

40. Step-Down/Up DC-DC Converter The output voltage can be higher or lower than the input voltage. Applications are where a negative polarity output is desired wrt to the common terminal of the input

41. Step-Down/Up DC-DC Converter:

42. Step-Down/Up DC-DC Converter: