A Study on Common-Mode Noise Generation in Switching Circuit due to Unbalanced Characteristic

General switching converter such as the simple high-side switching circuit inherently has unbalanced characteristics of impedance of transmission path, voltage at dc source and load terminals with respect to the frame ground. These unbalanced characteristic effects are the cause of unbalanced voltages at both dc source and load terminals. These unbalanced voltages will produce common-mode noise flowing through frame ground to the LISN during the active switch turn-off and on. This paper presents the analytical and experimental consideration of common-mode noise generation due to the unbalanced effect. The mechanism of common-mode noise generation due to unbalanced effect can be explained by equivalent circuit in both turn-off and turn-on time of the active switch. For common-mode noise reduction, the method for balancing the switching converter is also presented. Common-mode noise generated due to the effect of circuit imbalance is clarified by the experimental results. The balanced switching converter can greatly reduce the common-mode noise is also confirmed by the experimental results.