| 摘要 |
PROBLEM TO BE SOLVED: To prevent the wrong expansion of an air bag by the ignition of a squib by providing a failure detecting means for successively applying a driving power to switching transistors and detecting the failure of a switching transistor from the driving state of each switching transistor. SOLUTION: The ON resistance of each of a plurality of switching transistors HS1, HS2,... and LS1, SL2,... for squib ignition is set to a sufficiently large value such that a squib 1 is never ignited in the ON state of the single switching transistor HS1,.... In the failure check of each switching transistor HS1, HS2,... and LS1, LS2,..., each switching transistor HS1, HS2,... and LS1, LS2,... is successively laid in the ON state. Even if a power source short circuit or ground short circuit of a vehicle occurs in the upstream side and/or downstream side of the squib 1, the wrong expansion of an air bag by the ignition of the squib 1 can be prevented.
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