Analysis of effects of MOSFET parasitic capacitance on non-synchronous buck converter electromagnetic emission

Abstract

This paper aims to extract the correlation between parasitic capacitances of the Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and its influence in Electromagnetic (EM) Emission level of non-synchronous buck converter. In order to validate the proposed concept, the non-synchronous buck converter is designed and validated with dissimilar kind of MOSFETs which have different parasitic specifications. The effect of parasitic capacitance in MOSFET switching and transient characteristics are analyzed with time domain waveforms and the resultant electromagnetic emission due to those switching transients are analyzed and correlated with practical electromagnetic radiated and conducted emission results. The analysis and testing results shows the significant role of MOSFET parasitic capacitances in determining MOSFET switching transients, controlling the magnitude of electromagnetic emission and determining the frequency of EM noise propagation. Along with the time domain and frequency domain analysis the near field Electromagnetic scanning also performed to prove the proposed concept and reason for targeting MOSFET parasitic elements alone to control the EM emission level of the converter. The obtained results provide the evidence of controlling Electromagnetic emissions is possible with optimal selection of MOSFET parasitic capacitances without any additional control or filter circuits.

Keywords

• Buck converter
• Electromagnetic emission
• MOSFETs
• Parasitic capacitance
• Radiated emission
• Conducted emission