| 摘要 |
<p>This invention relates to electromagnetic interference emission suppression systems and, more particularly, to such a system for suppressing such interference in small, electrical equipment such as portable hand tools. Differential mode conducted interference is conventionally suppressed by connecting a capacitor between the A.C. power leads. One prior art technique for suppressing common mode interference is connecting a capacitor between each of the two A.C. power leads and the ground lead to short out or by-pass the interference. The required capacitance value are empirically determined by the type of equipment and the suppression standard to be met. If the ground connection is partly or wholly defective, the case becomes electrically energized and an equipment user experiences a low energy shock. If one of the common mode suppression capacitors shorts, the appliance is then electively connected to the A.C. power leads and if the ground connection should be defective, an equipment user may experience a very serious, and occasionally fatal, shock According to the present invention, differential mode interference is suppressed by connecting a capacitor across the power lines and common mode interference is suppressed by an inductor inserted in the ground lead, preferably within the equipment housing. The capacitor and inductor have substantially fixed values regardless of the type of equipment. In the preferred embodiment, inductor is constructed by winding a few turns of the ground lead itself through a high permeability, ferrite toroid positioned within the housing.</p> |
