Switched-Mode DC Power Supplies Five configurations –Flyback –Forward –Push-pull –Half...
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Transcript of Switched-Mode DC Power Supplies Five configurations –Flyback –Forward –Push-pull –Half...
Switched-Mode DC Power Supplies
• Five configurations– Flyback– Forward– Push-pull– Half Bridge– Full-Bridge
• Operate at high frequencies– Easy to filter out harmonics
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
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
Push-Pull Operation• Q1 ON, Vs across the lower primary winding
• Q2 ON, Vs across the upper primary winding