ECE 442 Power Electronics 1
Switching-Mode Regulators
Convert an unregulated DC voltage into a regulated DC voltage
ECE 442 Power Electronics 2
Buck Regulator
BJT Chopper L-C Filter Load
Control Voltage Freewheeling Diode
Output Voltage is Less Than the Input Voltage
ECE 442 Power Electronics 3
Mode 1 Operation – Q1 switched ON
Input current flows through L, C, and the Load – rises linearly
ECE 442 Power Electronics 4
Mode 2 Operation – Q1 switched OFF
Inductor current continues to flow through L, C, the Load, and Dm, falling linearly until Q1 is turned ON again.
ECE 442 Power Electronics 5
Waveforms for the Buck Regulator
ECE 442 Power Electronics 6
Summary for the Buck Regulator
• The peak-to-peak ripple current is
• The peak-to-peak ripple voltage is
(1 )sV k kI
fL
2
(1 )
8s
c
V k kV
LCf
ECE 442 Power Electronics 7
Summary for continuous current case
• The critical value of the inductor is
• The critical value of the capacitor is
(1 )
2c
k RL L
f
2
1
16c
kC C
Lf
ECE 442 Power Electronics 8
Boost RegulatorOutput Voltage is Greater Than the Input Voltage
ECE 442 Power Electronics 9
Mode 1 Operation – M1 switched ON
Input current flows through L and M1 (linearly)
ECE 442 Power Electronics 10
Mode 2 Operation – M1 switched OFF
Current that flowed through the transistor now flows through L, C, the Load, and diode Dm until transistor M1 is turned ON again.
ECE 442 Power Electronics 11
Waveforms for the Boost Regulator
ECE 442 Power Electronics 12
Summary for the Boost Regulator
• The peak-to-peak ripple current is
• The peak-to-peak ripple voltage is
sV kIfL
ac
I kV
fC
ECE 442 Power Electronics 13
Summary for continuous current case
• The critical value of the inductor is
• The critical value of the capacitor is
(1 )
2c
k k RL L
f
2c
kC C
fR
ECE 442 Power Electronics 14
Buck-Boost Regulator
The output voltage could be less than or greater than the input voltage
The polarity of the output voltage is opposite to the polarity of the input voltage Vs – Inverting Regulator
ECE 442 Power Electronics 15
Mode 1 Operation – Q1 turned ON
Input current flows through inductor L and Q1 linearly.
ECE 442 Power Electronics 16
Mode 2 Operation – Q1 switched OFF
Current flowing through L now flows through L, C, Dm and the Load.
ECE 442 Power Electronics 17
Waveforms for the Buck-Boost Regulator
ECE 442 Power Electronics 18
Summary for the Buck-Boost Regulator
• The peak-to-peak ripple current is
• The peak-to-peak ripple voltage is
sV kIfL
ac
I kV
fC
ECE 442 Power Electronics 19
Summary for continuous current case
• The critical value of the inductor is
• The critical value of the capacitor is
2c
kC
fR
(1 )
2c
k RL L
f
ECE 442 Power Electronics 20
Converter with a highly inductive Load
Input Current is “pulse” shaped
ECE 442 Power Electronics 21
Connect an input filter
Filter out the converter-generated harmonics from the supply line.
ECE 442 Power Electronics 22
Equivalent circuit for the converter-generated harmonic currents
ECE 442 Power Electronics 23
Example 5.10
ECE 442 Power Electronics 24
Buck Chopper for PSpice Simulation
ECE 442 Power Electronics 25
Results from PSpice
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Fourier Coefficients of the input current
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Vs110 V
Q1
BJT_NPN_VIRTUAL*
L1681.82uH
L240.91uH
C18.33uF
R12 Ohm
D1DIODE_VIRTUAL
XFG1R2250 Ohm
46
7
8
R31 Ohm
1
5
Vx0 V
3
0
Vy
0 V 11
12
Example 5.10 in MultiSim
ECE 442 Power Electronics 28
ECE 442 Power Electronics 29
Fourier Coefficients of the Input Current
ECE 442 Power Electronics 30
ECE 442 Power Electronics 31
ECE 442 Power Electronics 32