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EE 136 Project Presentation

EE 136 Project Presentation. The Diagonal Half-Bridge Flyback Converter Non-isolated Self-Oscillating Flyback Converter with Primary Current-Mode Control Isolated Self-Oscillating Flyback Converter with Primary Current-Mode Control Presented By: Latt M. Tee Naw Sandar Shwe.

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EE 136 Project Presentation

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  1. EE 136 Project Presentation • The Diagonal Half-Bridge Flyback Converter • Non-isolated Self-Oscillating Flyback Converter with Primary Current-Mode Control • Isolated Self-Oscillating Flyback Converter with Primary Current-Mode Control • Presented By: Latt M. Tee Naw Sandar Shwe

  2. The Diagonal Half-Bridge Flyback Converter • This converter is suitable for power FETs operation • Same design procedure applies as a single-ended flyback converter

  3. Circuit Analysis for Half-Bridge Flyback Converter • Switches is driven by control circuit, both “on” and “off” together • Flyback action takes place during “off” period • Cross-connected diodes D1 and D2 return excess flyback energy to supply lines • D1 and D2 eliminates the need of an energy recovery winding or large snubbing components.

  4. Schematic Diagram for Half-Bridge Flyback Converter

  5. The Circuit Diagram When Switches ‘On’ & ‘Off’ and Voltage and Current Waveform

  6. Schematic DiagramVoltage and Current waveforms (using Simplorer Software)

  7. Advantages of this converter • Using the diodes D1 and D2 is good for over-voltage stress. • Flyback action returns the stored energy to the supply line. • Do not need bifilar-wound energy recovery winding • Reduce the cost and eliminate unreliable source.

  8. Self-oscillating flyback converter • Low component count without loss of performance • Widely used in low power applications such as computers, video display terminals and so on

  9. Frequency variation as a function of loadNon-isolated self-oscillating flyback converter • Type C operation • Variable ‘on’ time, ‘off’ time, and repetition rate (freq.) • Has a more desirable characteristic

  10. Circuit Diagram of non-isolated flyback converter

  11. Base drive current waveform of self-oscillating converter

  12. Schematic and waveforms using Simplorer software

  13. Isolated self-oscillating flyback converter • The input and output voltage does not depend on each other • Optocoupler is used as a feedback loop • Transistor Q2 and R4 control the current-mode • Input voltage +300 V DC and output voltage +12V is applied to the circuit for self-oscillating

  14. Non-isolated self oscillating circuit

  15. The wave form of Q1 and Q2 • Q1 Ic increase Ie increase • Vbe 0.6V Q2 turn on

  16. Simulation result

  17. Advantages • The system as if the primary is a high-impedance current source. • Results in a first order transfer function. • The control circuit may have high frequency response. • Line ripple rejection and stability improved. • Primary current limiting is provided.

  18. Conclusion • Low cost • Fewer components need • Widely used in low power application

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