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10-1 Chapter 10 Switching DC Power Supplies • One of the most important applications of power electronics
38

10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

Jan 15, 2016

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Page 1: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-1

Chapter 10

Switching DC Power Supplies

• One of the most important applications of power electronics

Page 2: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-2

Linear Power Supplies

• Very poor efficiency and large weight and size

Page 3: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-3

Switching DC Power Supply: Block Diagram

• High efficiency and small weight and size

Page 4: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-4

Switching DC Power Supply: Multiple Outputs

• In most applications, several dc voltages are required, possibly electrically isolated from each other

Page 5: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-5

Transformer Analysis

• Needed to discuss high-frequency isolated supplies

Page 6: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-6

PWM to Regulate Output

• Basic principle is the same as discussed in Chapter 8

Page 7: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-7

Flyback Converter

• Derived from buck-boost; very power at small power (> 50 W ) power levels

Page 8: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-8

Flyback Converter

• Switch on and off states (assuming incomplete core demagnetization)

Page 9: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-9

Flyback Converter

• Switching waveforms (assuming incomplete core demagnetization)

Page 10: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-10

Other Flyback Converter Topologies

• Not commonly used

Page 11: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-11

Forward Converter

• Derived from Buck; idealized to assume that the transformer is ideal (not possible in practice)

Page 12: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-12

Forward Converter: in Practice

• Switching waveforms (assuming incomplete core demagnetization)

Page 13: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-13

Forward Converter: Other Possible Topologies

• Two-switch Forward converter is very commonly used

Page 14: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-14

Push-Pull Inverter

• Leakage inductances become a problem

Page 15: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-15

Half-Bridge Converter

• Derived from Buck

Page 16: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-16

Full-Bridge Converter

• Used at higher power levels (> 0.5 kW )

Page 17: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-17

Current-Source Converter

• More rugged (no shoot-through) but both switches must not be open simultaneously

Page 18: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-18

Ferrite Core Material

• Several materials to choose from based on applications

Page 19: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-19

Core Utilization in Various Converter Topologies

• At high switching frequencies, core losses limit excursion of flux density

Page 20: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-20

Control to Regulate Voltage Output

• Linearized representation of the feedback control system

Page 21: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-21

Forward Converter: An Example

• The switch and the diode are assumed to be ideal

Page 22: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-22

Forward Converter:Transfer Function Plots

• Example considered earlier

Page 23: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-23

Flyback Converter:Transfer Function Plots

• An example

Page 24: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-24

Linearizing the PWM Block

• The transfer function is essentially a constant with zero phase shift

Page 25: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-25

Gain of the PWM IC

• It is slope of the characteristic

Page 26: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-26

Typical Gain and Phase Plots of the Open-Loop Transfer Function

• Definitions of the crossover frequency, phase and gain margins

Page 27: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-27

A General Amplifier for Error Compensation

• Can be implemented using a single op-amp

Page 28: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-28

Type-2 Error Amplifier

• Shows phase boost at the crossover frequency

Page 29: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-29

Voltage Feed-Forward

• Makes converter immune from input voltage variations

Page 30: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-30

Voltage versus Current Mode Control

• Regulating the output voltage is the objective in both modes of control

Page 31: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-31

Various Types of Current Mode Control

• Constant frequency, peak-current mode control is used most frequently

Page 32: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-32

Peak Current Mode Control

• Slope compensation is needed

Page 33: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-33

A Typical PWM Control IC

• Many safety control functions are built in

Page 34: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-34

Current Limiting

• Two options are shown

Page 35: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-35

Implementing Electrical

Isolation in the Feedback Loop

• Two ways are shown

Page 36: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-36

Implementing Electrical Isolation in the Feedback Loop

• A dedicated IC for this application is available

Page 37: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-37

Input Filter

• Needed to comply with the EMI and harmonic limits

Page 38: 10-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 10 Switching DC Power Supplies Chapter 10 Switching DC Power Supplies One of the most important.

10-38

ESR of the Output Capacitor

• ESR often dictates the peak-peak voltage ripple