Digital Slew Rate and S-Shape Control for Smart Power Switches to Reduce EMI Generation

Smart power switches are power switches with integrated control and protection functions for the switching of middle- and high-current loads. In particular in automotive applications, smart power switches have to be operated without additional stabilization networks, EMI filters, and heat sinks to keep the weight, required space and costs of the circuit boards as low as possible. Therefore, the generated electromagnetic emissions must be reduced by another measure without significantly increasing the switching losses. This can be achieved by the active control of the first and/or second derivative of the output voltage. This paper presents a digital slew rate control and its extension to an S-shape control strategy, which in addition to the slew rate, also controls the second derivative of the output voltage. Both strategies are based on feedforward gate current profiles, which are iteratively adapted by an iterative learning control strategy to compensate for load variations and temperature dependences. A rapid prototyping test bench is presented, and the performance and robustness of the control strategies are demonstrated by a series of measurement results. An EMC compliance test according to the CSIPR 25 standard shows that the generation of conducted electromagnetic emissions can be reduced in a power efficient way by the proposed approach.