Diagnostic system for measurement of 'back-up' capacitor in test of 'hold up' circuitry in vehicle airbag control system

摘要

The diagnostic system for measuring the capacitance of a 'back-up' capacitor (12) includes a test circuit (10) with a clamp circuit incorporating a zener diode (13) and transistor (14) in parallel with the capacitor. By means of a load resistor (11) in addition to the zener diode and transistor, a current flows during a time interval, in which the transistor is switched by a microprocessor (4), and the clamping voltage of the capacitor is limited to a predetermined voltage.