Design, analysis, simulation and modeling of a soft-switching unbalanced asymmetrical half-bridge DC-DC converter

This thesis discusses a soft-switching unbalanced asymmetrical half-bridge pulse width modulated (PWM) DC-DC converter that can be used in telecommunications and network power applications. In addition, a new modeling method for isolated PWM DCDC converters is proposed.; A detailed review of the operation of the asymmetrical half-bridge is presented. The relative advantages and disadvantages of the asymmetrical half-bridge are presented with respected to the active clamp forward converter. In addition, the converter steady-state equations and waveforms are presented. Details of the switching transitions and their relevance to soft-switching are given along with a quantitative analysis of the energy requirements to achieve soft-switching. Design details are included for the converter transformer, blocking capacitance, output filter and control loop. Simulation and experimental results are presented for a 30W, 5V output prototype of the asymmetrical half-bridge built on a printed circuit board using surface mount technology. The results presented include steady-state waveforms and small-signal dynamic Bode diagrams. The efficiency of the prototype was measured across the entire input voltage range of 35V to 75V at load currents between 2A and 6A. A peak efficiency of 89.8% was achieved.; A large-signal averaged circuit model for isolated PWM DC-DC converters is presented. The model can be used for converters under current, or voltage mode control. The current mode control model is a general model applicable to all isolated PWM DC-DC converters which use the current signal from the active switch for the control. The model is very simple to implement in order to analyze PWM converter topologies because the model circuit topology takes the same form as the switching converter that it is derived from. Models are presented for the asymmetrical half-bridge and the active clamp forward topologies. Simulation and experimental results are presented for the asymmetrical half-bridge to verify the small-signal and large-signal versions of the model.