A Simple Large Signal Model for Isolated DC-DC Converters

In this paper, a large signal model for isolated DC-DC converters is proposed. The model is applicable to both current and voltage mode control. The model has the principle advantage that it is simple to derive-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 active switch and its corresponding synchronous rectifier are replaced by dependent average current sources. In multiple switch topologies, the additional switches are replaced by dependent average voltage sources. Implementation of the model is very simple since no mathematical derivations are required. The only change to the circuit is the replacement of the switches by their dependent sources. The model is simple to implement in circuit simulation software packages such as SPICE. Once implemented, small signal and large signal behaviour can be obtained through simulation. The model is verified experimentally for the small signal and large signal cases using a prototype of the asymmetrical half-bridge topology operating at 48 V input, and 5 V at 6 A load and a 400 kHz switching frequency. Good agreement is obtained between the simulation and experimental results validating the model