Evaluation of Failure Threshold of Digital Control Circuit Under Mixed Electromagnetic Interference of Electrical Fast Transient and Surge

Digital control circuits failure problem usually occurs in electronic equipment working in a mixed electromagnetic environment. Therefore, it is necessary to study the failure mechanism of digital control circuits under mixed electromagnetic interference (EMI) and electromagnetic compatibility (EMC) design method to the failure problem. The digital circuit failure behaviors under mixed EMI of electrical fast transient (EFT) and surge are tested and analyzed. This article innovatively proposes an evaluation method of failure threshold of digital control circuits, that can be applied to the case where both voltage and current may change under mixed EMI of EFT and surge. The proposed evaluation method is dependent on the instantaneous product of amplitude and slope of the power supply port voltage of the regulator chip. The port voltage transfer characteristic of the regulator chip expressed using transfer function under mixed EMI is obtained. Then, the coupling model of mixed EMI of EFT and surge on the digital circuit board is built. The coupling model is validated by comparing the simulated results and measured results in 1000 V EFT and 20 V surge test. Based on the coupling model and the failure threshold, an evaluation method of circuit failure state under mixed EMI of EFT and surge is introduced and verified. Furthermore, an anti-interference filter design method is presented. Through a prototype experiment, the anti-interference filter design method is validated.