Drive circuit for vehicle occupant safety apparatus

摘要

A drive circuit for a vehicle occupant safety apparatus includes a device for activating the vehicle occupant safety apparatus. A first transistor is connected in series with the device. A constant-current circuit receives electric energy from a power supply, and feeds a constant current to the device when the first transistor falls into its on state. The constant-current circuit includes a second transistor connected in series with the device. The second transistor includes an N-channel field-effect transistor. A third transistor is connected to the second transistor. The second and third transistors form a current mirror circuit. The third transistor includes an N-channel field-effect transistor. A voltage between a gate and a source of the third transistor is regulated at a constant level. Gate voltages of the second and third transistors are controlled in response to source voltages of the second and third transistors to equalize the source voltages of the second and third transistors.