Averaged Small Signal Model of a Push-Pull Converter with Parasitic Elements in Continuous Mode

This paper presents the small-signal modeling of a modified push-pull converter using averaged circuit method. Parasitic elements are considered to increase the accuracy of the proposed technique. In the design process of converters it is desirable to assess as many critical design parameters and parasitic effects by simulation as possible, since the control is hard to tune after fabrication. The low frequency small-signal model is done using state space averaging technique and two main power-stage transfer functions are derived, which are control-to-output voltage transfer function and input-to-output voltage transfer function. Using the proposed model of the converter we can analyze and simulate the time domain transient behavior of the system accurately and intuitively. The resulting model is a time averaged equivalent circuit model where all branch currents and node voltages correspond to their averaged values of the corresponding original currents and voltages. The model is applicable to both current and voltage mode control. The model has the principle advantage that it is simple to derive and it takes the same form as the switching converter that it is derived from. In the model, the MOSFET switches are replaced by dependent current and voltage sources equal to the average current through the switch, or average voltage across the switch. The validity of the proposed model was verified by simulation and experimental results for a specified design example. The method of modelling presented here helps to design the inverter effectively and better choosing the controller component values. /p