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

ECE 442 Power Electronics 26

Fourier Coefficients of the input current

ECE 442 Power Electronics 27

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