A chaos-modulated ramp generator IC for flexible EMI reduction in voltage-mode controlled PWM buck converters

It is well known that switching power electronic converters generate electromagnetic interference and consequently, suppression of EMI is a very important issue in SMPS design. Earlier, chaos-based spectral modification was proposed to counter the cost and weight problems of the traditional LC filters and screening methods of suppressing EMI. In this scheme, a voltage-mode controlled converter is designed to operate in the conventional periodic mode, while the ramp is given a chaotic jitter about the mean frequency. This reduces harmonic power level of the inductor current and thus suppresses both conducted and radiated EMI. A ramp-generator IC has been designed in a 0.5 mu BiCMOS technology on this scheme as a product to be used with existing VMC converters. A prototype has been tested on a buck converter operating under voltage mode control and significant reduction in harmonic power level has been observed. Moreover, it has been designed with a tuning feature which enables the user to adjust the same hardware externally to conform to varying EMI reduction requirements. The present paper briefly reviews the existing schemes for chaotic modulation and discusses the experimental results with this IC.