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EMI Filter Improvement: Cancellation of Winding Capacitance of Filter Inductor

Fig. 1. CM noise reduction after applying the proposed parasitic
capacitance cancellation technique in a boost PFC converter.
Common mode (CM) noise is a major concern in EMI suppression because it is resulted from the high dv/dt, which is a nature of switching mode power converters, in power electronics circuits. The high dv/dt nodes in power circuits can cause CM EMI noise via the parasitic capacitance between the high dv/dt node and the heat-sink or the ground. CPES has developed a method of generating a negative capacitance to cancel the parasitic capacitance between the high dv/dt node and the heat-sink or the ground. Because the parasitic capacitance is canceled, CM noise path is terminated. The CM noise is greatly reduced. There is a 20-30dB CM noise reduction after applying this technique in a boost PFC converter.

Fig. 2. Cancellation of CM parasitic capacitance between the drain of MOSFET and heat-sink.
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