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Heavy Load Simulation Model of Flyback Switching DC-DC Converters and its Application for Reliability Improvement

This paper presents the simulation model of flyback switching DC-DC converters operating in heavy load modes, and the application of the model in the converter design for improving the system reliability. To derive the simulation model, different operational modes and atomic circuit blocks (ACB) are established first. Then, the state-machine of the system is studied. Finally, the transfer function of each ACB is determined, and according to the relationship among the ACBs, the complete simulation model is built, which can be used for transient analysis during starting, the operation in the under-voltage mode or over-current mode. Furthermore, the heavy load simulation model is applied to calculate the maximum steady-state power loss of the output diode, one of the key factors for thermal analysis which is crucial for the system reliability. The effect of time delay is also considered. By modifying the parameters of a physical flyback converter according to the simulation results, the converter reliability is significantly improved. The theoretical analysis is verified by experimental results.