Abstract: A person-on-board protecting apparatus having ignition timing estimating means for outputting an ignition signal by determining a collision on the basis of an output from an acceleration sensor and estimating timing at which the head of a person on board reaches a predetermined position, expansion rate control means for outputting a control signal for controlling the expansion force of an air bag according to the head position of the person on board from a forward predetermined reference position, and an inflator having a plurality of detonators. The ignition modes of the plurality of detonators provided for the inflator are controlled according to an ignition signal from the ignition timing estimating means and a control signal from expansion force control means, so that the expansion rate and timing of the air bag are controlled.

Abstract: The invention relates to circuits which increase the reliability of a passenger restraint system. In one embodiment, the connection layout with respect to a main power source, such as a vehicle battery, prevents accidental activation in the event certain portions of the wiring become grounded and which enables the activation when required even when some of the wiring is cut. Another embodiment increases the time for a which a diagnostic system can be maintained operative should the connection with the vehicle battery be lost. A third and more complex embodiment features circuits which can estimate the amount of damage which has occurred to the vehicle and predict the displacement of person under the influence of the acceleration (deceleration) caused by a collision.