Modeling EMI Problems Associated with DC-DC Converters

Abstract —This work presents the analysis of radiated EMI problems associated with DC-DC buck converters and the solutions for minimize the reverse recovery of the Drain-Bulk diode of the synchronous switching MOSFET. The DC-DC buck converter topology is used in computers and telecom applications because of its high power efficiency and multiple DC levels. For reducing the reverse recovery and its related EMI radiation is used a technique with monolithically integrated Schottky diodes. I. I NTRODUCTION With the increase of switching frequency of electronic switches, power converters have raised more and more electromagnetic energy pollution to the local environment. Electromagnetic compatibility (EMC) and electromagnetic interference (EMI) norms applied to power converters have objective to reduce conducted and radiated perturbances. Radiated EMI appears in the form of electromagnetic waves directly from the circuitry. The circuitry and its interface can influence themselves or the transmitting antenna for this radiated EMI emission. This emission is generally measured at much higher frequencies than their conducted counterparts, namely beyond 30 MHz up to several GHz [2]. The new generations of microprocessors are powered by local low voltages but high currents power supplies. Due to connector and power loss issues, power cannot be delivered by a remote power supply at the desired DC voltage. In addition, the fast transient current demand requires the power source being located close to the microprocessors. The most commonly used voltage regulator design is based on the synchronous buck topology. The input power supply voltage is stepped down to the operating voltage needed by the microprocessor. DC-DC converters operate at switching frequencies up to a few MHz. The potential EMI problem has been well covered in the literatures [3], [4]. By operating a DC-DC converter with the soft switching scheme without disturbing its averaged duty cycle, it is possible to eliminate predominant harmonics present in the input current to reduce overall peak amplitude of the frequency spectrum. The spreading spectrum concept has been applied successfully for the mitigation of conducted harmonic interference of the DC-DC buck converters [5]. Using of high switching frequencies in DC-DC converters allows magnetic components to be minimized but also enhanced the spectrum of EMI caused by interaction of the active components. II. P