Control circuit for vehicle occupants safety device, such as airbag

摘要

A control circuit for a vehicle passenger/occupants safety device has a device (11) to activate the safety device, a transistor (13) in series with it, a power supply (1,2) and a constant-current circuit which receives energy from the power supply and feeds a constant current into the device mentioned above if the transistor is switched on. The constant-current circuit has a second transistor (15) in series with the device and an N-channel field effect transistor. It has a third transistor (19) connected to the second one to form a current mirror circuit. The third transistor "has" an N-channel field effect transistor (FET). The circuit has a first device (20) to keep a voltage between a gate and a source of a third transistor (19) at a constant level and a second device (21 to 23) to control the gate voltages of the second and third transistors in response to their source voltages in order to make their source voltages equal.