Fault tolerant air bag bus system without transformer

The invention relates to air bag systems for cars. shows a conventional air bag system consisting of a number of firing stages , , a microcontroller and a crash sensor . The firing stages , switch ignition currents through squibs , to fire the air bag at the appropriate time during a crash of the car. A high number of squibs requires a large number of wires, since two wires per squib are needed. Short circuits of these wires to ground or the battery voltage may cause unwanted firing of the airbags. A fault tolerant air bag system needs a floating supply, which supply conventionally is made by means of a DC-DC converter with a transformer. By splitting the main energy reserve capacitor () into two capacitors (), and coupling one of the capacitors () to the other () by means of switches () which open during a crash, no transformer is needed any more.