Title: Power Semiconductor Devices
1Power Electronics
Chapter 5 DC to DC Converters
(Choppers)
2Outline
- 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 )
35.1 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
45.1 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
5Dc component of switch output voltage
Fourier analysis Dc component average value
6Insertion of low-pass filter to remove switching
harmonics and pass only dc component
7Basic operation principle of buck converter
Buck converter with ideal switch
Realization using power MOSFET and diode
8Thought 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
9Actual output voltage waveform of buck converter
Buck convertercontaining practicallow-pass
filter
Actual output voltagewaveform
v(t) V vripple(t)
10The 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
11Buck converter analysisinductor current waveform
12Inductor voltage and currentsubinterval 1
switch in position 1
13Inductor voltage and currentsubinterval 2
switch in position 2
14Inductor voltage and current waveforms
15Determination of inductor current ripple magnitude
16Inductor current waveform during start-up
transient
17The principle of inductor volt-second balance
Derivation
18Inductor volt-second balanceBuck converter
example
19The principle of capacitor charge balance
Derivation
20Boost converter example
21Boost converter analysis
22Subinterval 1 switch in position 1
23Subinterval 2 switch in position 2
24Inductor voltage and capacitor current waveforms
25Inductor volt-second balance
26Conversion ratio M(D) ofthe boost converter
27Determination of inductor current dc component
28Continuous-Conduction-Mode (CCM) and
Discontinuous-Conduction-Mode (DCM) of buck
Electronics
Power
28
29Continuous-Conduction-Mode (CCM) and
Discontinuous-Conduction-Mode (DCM) of boost
Electronics
Power
29
305.2 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
315.2.1 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
32Bridge chopper (H-bridge chopper)
- Can be considered as the combination of two
current-reversible choppers. - Can realize 4-quadrant operation of DC motor.
33Multi-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.
345.3 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
35Classification 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
365.3.1 Forward converter
- Simple, low cost
- Uni-polar transformer current, low power
applications
375.3.2 Flyback converter
- Simple, low cost
- Uni-polar transformer current, low power
applications
385.3.3 Half bridge converter
- Cost higher than forward and flyback converter
- Bi-polar transformer current, up to several
kilowatts
395.3.4 Push-pull converter
- Cost higher than forward and flyback converter
- Center-tapped transformer
405.3.5 Full-bridge converter
- Cost is even higher
- Bi-polar transformer current, up to several
hundreds of kilowatts
415.3.6 Rectifier circuits in the isolated DC to
DC converters
Full-wave rectifier
Full-bridge rectifier
Synchronous rectifier
425.3.7 Configuration of 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
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