Application of Y-cap on noise attenuation in low power part of power converter

The high frequency voltage oscillation on the DC/DC gate driver of a H-bridge created during the turn-off intervals of the power switches has critical impact on component reliability and control quality. This noise can propagate freely in the low power plane to other functional circuits of the converter due to the performance degradation of EMI filter in high frequency range above 30MHz. In this paper, the origin of the high frequency voltage oscillation is analyzed and a new way of utilizing Y-cap is proposed to reduce this voltage oscillation before it propagates in the low power plane. The key idea is to provide a current return path with low impedance at the oscillation frequency from the input of DC/DC gate driver to the switches. Therefore, the high frequency voltage drop on DC/DC gate driver is attenuated. The proposed approach is practically effective to improve noise performance of a converter at the final stage design and maintenance phase with minimum efforts of calculation and measurement. To support the analysis, the experiments with a Buck converter with a typical H-bridge driver circuit are performed. Several combinations of Y-caps are used to prove the effectiveness of the proposed method.