Design and Development of R-load Monitoring and Control Interface for Optimization of Pre-EMC Compliance Test Laboratory

During electromagnetic interference (EMI) noise immunity tests of Switched-Mode Power Supply (SMPS), Test Engineers (TE) need to be physically present to manually monitor and control the resistive load (r-load) and fan parameters. This practice is prone to human error and, thus, results in accuracy and safety concerns impacting time-to-market and product development costs. To solve this, an EMI-noise immune interface that supports the existing test automation software to remotely monitor and control r-load and fan parameters was designed and developed. The interface has five blocks: the internal supply circuit, the monitoring circuit, the power control circuit, the microcontroller circuit, and the EMI noise protection and filter circuits. For supplies of internal circuitries, a flyback converter is used to provide isolated biases needed to maintain separation between power and communication circuits. For voltage and current monitoring, sense resistors and differential amplifiers are used taking into consideration the component variations’ impact on accuracy. For power control, MOSFET driven by a transistor switch is used taking into consideration the components’ electrical stresses. For EMI noise mitigation, filters and protective devices are placed on the power lines and shielded I2C lines where the interface and test computer communicate. Test results showed that the interface has > 95% monitoring precision and accuracy and has 100% control reliability at operating temperatures from -40˚C to 75˚C. Furthermore, it is compliant to class B EMI noise emission and level 3 EMI noise immunity test standards. Therefore, the interface, together with the existing test automation software, may be used for EMI noise immunity tests improving the accuracy of the test while reducing safety risks which optimizes the pre-EMC compliance test laboratory.