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Power Semiconductor Devices

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Title: Power Semiconductor Devices Author: jackywang Last modified by: T42 Created Date: 10/12/2002 7:32:00 AM Document presentation format: – PowerPoint PPT presentation

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Title: Power Semiconductor Devices


1
Power Electronics
Chapter 5 DC to DC Converters
(Choppers)
2
Outline
  • 5.1 Basic DC to DC converters
  • 5.2 Composite DC/DC converters and
  • connection of multiple DC/DC converters
  • 5.3 Isolated DC to DC converters (Indirect DC
    to DC converters )

3
5.1 Basic DC to DC converters
  • 5.1.1 Buck converter (Step-down converter)
  • 5.1.2 Boost converter (Step-up converter)
  • 5.1.3 Buck-Boost converter (Step-down/step- up
    converter) and Cuk converter
  • 5.1.4 Sepic converter and Zeta converter

4
5.1 Basic DC to DC converters
IntroductionBuck converter
SPDT switch changes dc component
Switch output voltage waveform
Duty cycle D 0 D 1
complement DD 1 - D
5
Dc component of switch output voltage
Fourier analysis Dc component average value
6
Insertion of low-pass filter to remove switching
harmonics and pass only dc component
7
Basic operation principle of buck converter
Buck converter with ideal switch
Realization using power MOSFET and diode
8
Thought process in analyzing basic DC/DC
converters
  • Basic operation principle (qualitative analysis)
  • How does current flow during different switching
    states
  • How is energy transferred during different
    switching states
  • Verification of small ripple approximation
  • Derivation of inductor voltage waveform during
    different switching states
  • Quantitative analysis according to inductor
    volt-second balance or capacitor charge balance

9
Actual output voltage waveform of buck converter
Buck convertercontaining practicallow-pass
filter
Actual output voltagewaveform
v(t) V vripple(t)
10
The small ripple approximation
v(t) V vripple(t)
In a well-designed converter, the output voltage
ripple is small. Hence, the waveforms can be
easily determined by ignoring the ripple
11
Buck converter analysisinductor current waveform

12
Inductor voltage and currentsubinterval 1
switch in position 1
13
Inductor voltage and currentsubinterval 2
switch in position 2
14
Inductor voltage and current waveforms
15
Determination of inductor current ripple magnitude
16
Inductor current waveform during start-up
transient
17
The principle of inductor volt-second balance
Derivation
18
Inductor volt-second balanceBuck converter
example
19
The principle of capacitor charge balance
Derivation
20
Boost converter example
21
Boost converter analysis
22
Subinterval 1 switch in position 1
23
Subinterval 2 switch in position 2
24
Inductor voltage and capacitor current waveforms
25
Inductor volt-second balance
26
Conversion ratio M(D) ofthe boost converter
27
Determination of inductor current dc component
28
Continuous-Conduction-Mode (CCM) and
Discontinuous-Conduction-Mode (DCM) of buck
Electronics
Power
28
29
Continuous-Conduction-Mode (CCM) and
Discontinuous-Conduction-Mode (DCM) of boost
Electronics
Power
29
30
5.2 Composite DC/DC converters and connection of
multiple DC/DC converters
  • 5.2.1 A current-reversible chopper
  • 5.2.2 Bridge chopper (H-bridge DC/DC
    converter)
  • 5.2.3 Multi-phase multi-channel DC/DC
    converters

31
5.2.1 A current reversible chopper
Electronics
  • Can be considered as a combination of a Buck
    and a Boost
  • Can realize two-quadrant ( I II) operation
    of DC motor forward motoring, forward
    braking

Power
31
32
Bridge chopper (H-bridge chopper)
  • Can be considered as the combination of two
    current-reversible choppers.
  • Can realize 4-quadrant operation of DC motor.

33
Multi-phase multi-channel DC/DC converter
  • Current output capability is increased due
    to multi-channel paralleling.
  • Ripple in the output voltage and current is
    reduced due to multi- channel paralleling.
  • Ripple in the input current is reduced due
    to multi-phase paralleling.

34
5.3 Isolated DC to DC converters (Indirect DC to
DC converters )
  • Reasons to use indirect DC to DC structure
  • Necessary isolation between input and output
  • In some cases isolated multiple outputs are
    needed
  • The ratio of input and output voltage is far away
    from 1
  • Power semiconductor devices usually used
  • Inverter part Power MOSFETs, IGBTs
  • Rectifier part Fast recovery diodes, Schottky
    diodes, Synchronous rectifiers

35
Classification of isolated DC to DC converters
According to whether transformer current is
uni-direction or bi-directional
  • Single-ended converters
  • Forward converter
  • Flyback converter

Isolated DC to DC converters
  • Double-ended converters
  • Half bridge
  • Push-pull
  • Full bridge

36
5.3.1 Forward converter
  • Simple, low cost
  • Uni-polar transformer current, low power
    applications

37
5.3.2 Flyback converter
  • Simple, low cost
  • Uni-polar transformer current, low power
    applications

38
5.3.3 Half bridge converter
  • Cost higher than forward and flyback converter
  • Bi-polar transformer current, up to several
    kilowatts

39
5.3.4 Push-pull converter
  • Cost higher than forward and flyback converter
  • Center-tapped transformer

40
5.3.5 Full-bridge converter
  • Cost is even higher
  • Bi-polar transformer current, up to several
    hundreds of kilowatts

41
5.3.6 Rectifier circuits in the isolated DC to
DC converters
Full-wave rectifier
Full-bridge rectifier
Synchronous rectifier
42
5.3.7 Configuration of switching power supply
  • Linear power supply
  • Switching power supply

High frequencyAC
High frequency
Line frequencyAC input
Regulated DC output
AC
Inverter
Filter
Transformer
Rectifier
Rectifier
Filter
DC
Isolation
Indirect DC to DC converter
42
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