Power conditioning circuits have long been used to protect sensitive load equipment from transients caused by lightning strikes, noise and other power line disturbances. Traditionally, filter elements are used in the line and neutral conductors which trap and/or shunt unwanted power frequencies away from the load. See, for example, Speet et al. U.S. Pat. No. 4,814,941 and Taylor et al. U.S. Pat. No. 5,490,030.
Muelleman U.S. Pat. No. 5,448,443 discloses a power conditioning device and method including an isolation transformer having primary and secondary sides and a ground impedance connected between the secondary side of the isolation transformer at a safety ground and an earth ground. The Muelleman device prevents ground current loops by redirecting transient ground currents to neutral, but does not provide current limiting or noise suppression.
USPTO Backgrounds
USPTO Backgrounds