Transient responses of switching mode power supplies under a lightning surge

This paper discusses the transient responses of switching mode power supplies (SMPS) under a lightning surge. These devices are normally used in fluorescent lighting, personal computers and other appliances. In this paper the circuit models of switching mode power supplies are developed by taking into account both the nonlinearity and the parasitic effect of SMPS components. These models are verified experimentally by comparing the surge current in the devices under a voltage surge. It is found that the surge current primarily arises from capacitor charging caused by the surge voltage. These devices can be then represented simply by capacitor-charging circuits in the analysis of lightning surges, particularly for the discussion of load effect. It is noted that the currents under common-mode and differential-mode surges are significantly different in magnitude and waveform. It is also noted that the supply circuit could have a significant effect on the surge current if the circuit impedance is comparable to the choke impedance.