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

A circuit with which errors in the triggering circuit can be very reliably detected has a transistor bridge circuit in whose shunt arm a triggering arrangement and a capacitor are arranged. A measured current source is connected to the transistor bridge circuit. A controller controls the transistors and the measured current source during a monitoring cycle so that the capacitor is charged by a measured current. A sample-and-hold circuit controlled by the controller measures, after the capacitor has been charged, a first voltage drop across the triggering circuit and, after the measured current has been turned off, a second voltage drop across the triggering circuit so that the controller can determine the resistance of the triggering arrangement and the capacitance from these two voltages.