Use of low-pass filters to protect equipment from transient overvoltages on the mains

The design of commercial low-pass filter modules for equipment connected to the low-voltage supply mains is reviewed. Problems of using these filters to protect electronic equipment from damage or upset by high-voltage transients on the mains are discussed. The design and performance of circuits that incorporate both overvoltage protection and a low-pass filter are discussed. One circuit is designed for commercial environments, the other of medical equipment in patient care areas. Filters for medical equipment in patient care areas must have very small line-to-ground leakage currents, which make it difficult to provide either overvoltage protection or low-pass filtering. Using an overvoltage-protection low-pass filter is less expensive than using a line conditioner to protect equipment, and, in many instances, the filter may give satisfactory protection