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

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

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.

Schematic Diagram for Half-Bridge Flyback Converter

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

Schematic Diagram Voltage and Current waveforms (using Simplorer Software)

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.

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

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

Circuit Diagram of non-isolated flyback converter

Base drive current waveform of self-oscillating converter

Schematic and waveforms using Simplorer software

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

Non-isolated self oscillating circuit

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

Simulation result

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.

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