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Download Switched - Mode DC Power Supplies
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Transcript
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
