Transcript Switched - Mode DC Power Supplies

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 transistors are OFF
• D1 continues to conduct due to current in L1
Mode 3 Operation
• Q2 ON, D2 conducting
• Energy transferred to the load
Mode 4 Operation
• Both transistors OFF
• D2 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 are ON, Q1,Q4 OFF
• D2 conducting, energy transferred to the load
Mode 4 Operation
• All transistors are OFF
• D2 continues to conduct due to current in L1
Waveform Summary – k<0.5
Half-Bridge Resonant Inverter
Full-Bridge Resonant Inverter
Bidirectional Power Supply