Circuit for monitoring the ignition system for a safety device in an automobile

A circuit for triggering a safety device in a motor vehicle and for monitoring a triggering of the safety device, comprising:

• a triggering circuit including:
• a transistor bridge circuit including transistors and a shunt arm,
• a triggering arrangement corresponding to an ohmic resistance, and
• a capacitor connected in series with the triggering arrangement, the triggering arrangement and the capacitor being arranged in the shunt arm, and the capacitor being charged and discharged through the transistor bridge circuit;
• a measured current source connected to the transistor bridge circuit;
• a controller for controlling the measured current source and the transistors of the transistor bridge circuit during a monitoring cycle so that the capacitor is initially charged by a measured current and subsequently discharged;
• and
• a sample-and-hold circuit controlled by the controller, wherein:
• the sample-and-hold circuit measures a first voltage drop across the triggering circuit after the capacitor has been charged and a second voltage drop across the triggering circuit after the measured current source has been turned off, so that the controller is capable of determining the resistance of the triggering arrangement and a capacitance of the capacitor from the first voltage drop and the second voltage drop.