Date of Award
Doctor of Philosophy
Dr. N. Barry
This work presents the analysis and design of an isolated flyback converter, without feedback from the load side. The converter is controlled from the primary side using the switch voltage and innovative control circuit topologies.
A detail study of the flyback circuit is undertaken including all known parasitics. Besides the standard parasitics, for example the capacitor resistive effect, other more subtle effects are included in the model development such as inter coil couplingj source capacitance etc. Development of these models has provided information about circuit simplifications without losing accuracy of the model. As a consequence of this model development, it is possible to accurately calculate the load voltage from the switch voltage and to control the circuit performance.
The output voltage of the isolated flyback converter calculated on the primary side provides the load control information in each switching cycle, without the traditional feedback loop and the use of an opto-coupler to isolate the feedback signal. The information about the input line is also updated in each switching cycle. A novel control mechanism based on the line and the load regulation information provides primary side cycle by cycle voltage mode control of the flyback converter. With the control mechanism continuous, conduction mode and discontinuous conduction mode are possible in the same circuit, this extends the range of the converter load operations.
The control methodology is theoretically and experimentally verified. Variable frequency modulation is used in the power control with both variable on-time and variable off-time. The methodology can also be extended to Electromagnetic Interference (EMI) sensitive applications where a constant switching frequency is desirable.
The circuits proposed and discussed in this work have their own dedicated startup circuits. During the start-up they operate in current mode control to provide the shortest start-up times possible. The start-up circuits use a limited number of components suitable for incorporation into an integrated solution.
Nalepa, Radoslaw, "Analysis and Synthesis of Primary Side Cycle by Cycle Control of Isolated Flyback Converters" (2001). Theses [online].
Available at: https://sword.cit.ie/allthe/623