Patent ID: 7772714

Claim:
A passive safety device for vehicles comprising: a main power source; a backup power source that supplies voltage in place of the main power source when power supply from the main power source is interrupted; a switching element disposed between the main power source and a firing circuit; a drive circuit driving the switching element so that a predetermined voltage is supplied to the firing circuit; a power source for the drive circuit that is connected to the main power source and that supplies voltage to the drive circuit in place of the main power source when power supply from the main power source is interrupted, wherein the power source for the drive circuit is constructed of a capacitor charged by the main power source, the capacitor configured such that a voltage thereof drops more slowly than the voltage of the backup power source when power supply from the main power source is interrupted, and wherein the drive circuit includes: driver switching elements connected so as to construct a push-pull circuit for controlling the switching element; and means for operating the driver switching elements so as not to ground the output of the power source for the drive circuit through the driver switching elements.