Occupant protecting device for use in motor vehicles

A drive device for a vehicle occupant protecting device comprising:

• an auxiliary power source which is charged by a DC power source;
• an igniting device;
• a switching element connected between a point connecting the DC power source with said auxiliary power source and said igniting device;
• and
• a control circuit for judging a magnitude of a collision based on an acceleration signal supplied from an acceleration sensor to provide a trigger signal to said switching element thereby electrically connecting said auxiliary power source to said ignition device when it is judged that an accident has occurred, said control circuit detecting an output voltage of said auxiliary power source.
• wherein said control circuit comprising a pulse-width varying circuit for varying a pulse width of the trigger signal in inverse proportion to the output voltage,
• and wherein a predetermined energy necessary to fire said ignition device is determined by said output voltage and said pulse width, and said control circuit varies said pulse width to deliver said predetermined energy to said ignition device.