Abstract: A method and apparatus for suppressing electrical transient signals, occurring on power lines, includes a clamping circuit for switching from a high impedance to a low impedance at a certain switching voltage, to suppress the transient signals. A first blocking circuit inhibits the clamping circuit from switching to maintain it at its high impedance during normal line voltage, and permits the clamping circuit to switch to its low impedance for clamping purposes responsive to an initial portion of a transient signal for initial suppression purposes. A second blocking circuit has a second low impedance, which is substantially lower than said first low impedance of the first blocking circuit, for inhibiting substantially the first blocking circuit from continuing to dissipate the transient signal following the initial time period, and for permitting the clamping circuit to suppress the transient signal following the initial time period.

Abstract: Main power (e.g. an alternating voltage) is applied to a data processing system through a switch in a first state of the switch operation. The switch may have an arm movable to a first terminal to obtain the first state of switch operation and to a second terminal to obtain a second state of switch operation. A microprocessor periodically checks to determine if the main power to the data processing system has been interrupted. Upon such an interruption, the microprocessor produces a signal which causes the switch to be transferred to the second state of operation. The microprocessor is also operative to cause an alternating voltage to be produced during the interruption in the application of the main power to the data processing system. This alternating voltage is introduced to the data processing system in the second state of operation of the switch to energize the data processing system.