applications

Switch Mode Power
Supply(SMPS)



Prepared by
Dhrumil H. Sheth

Switched-Mode DC Power
Supplies




Five configurations


Flyback



Forward



Push-pull



Half Bridge



Full-Bridge

Operate at high frequencies


Easy to filter out harmonics

Flyback Converter

Mode 1 Operation -- Q1 ON
 Current

builds up in the primary winding
 Secondary winding has the opposite polarity D1
OFF
 C maintains the output voltage, supplies load
current

Mode 2 Operation -- Q1 turned OFF
 Polarity

of the windings reverses
 Diode D1 conducts, charging C and providing
current to the load RL
 Secondary current falls to 0 before the next
cycle begins

Waveform Summary

Double-ended Flyback
Converter

Forward Converter

Features
 Includes

a “reset” winding to return energy

 Secondary

“dot” so that D2 forward biased when
Q1 is ON – no energy stored in the primary

 Operates

in continuous mode

Mode 1 Operation -- Q1 ON
 Current

builds up in the primary

winding
 Energy

transferred to the load

Mode 2 Operation -- Q1
turned OFF
 Polarity

of transformer voltages

reverses
 D2

turns OFF, D1 and D3 turn ON

Waveform Summary

Vo

D3

Current Components in the
Primary

Double-ended Forward
Converter

Push-Pull Converter

Push-Pull Operation
 Q1

ON, Vs across the lower primary winding

 Q2

ON, Vs across the upper primary winding

Half-Bridge Converter

Mode 1 Operation
 Q1

ON, D1 conducting

 Energy

transferred to the load

Mode 2 Operation
 Both
 D1

transistors are OFF

continues to conduct due to current in L1

Mode 3 Operation
 Q2

ON, D2 conducting

 Energy

transferred to the load

Mode 4 Operation
 Both
 D2

transistors OFF

continues to conduct due to current in L1

Waveform Summary – k<0.5

Full-Bridge Converter

Mode 1 Operation
 Q1,Q4

ON, Q2,Q3 OFF
 D1 conducting, energy transferred to the load

Mode 2 Operation
 All

transistors are OFF
 D1 continues to conduct due to current in L1

Mode 3 Operation
 Q2,Q3
 D2

are ON, Q1,Q4 OFF

conducting, energy transferred to the load

Mode 4 Operation
 All
 D2

transistors are OFF
continues to conduct due to current in L1

Waveform Summary – k<0.5

Half-Bridge Resonant Inverter

Full-Bridge Resonant Inverter

Bidirectional Power Supply