Abstract: A device for driving a rotary solenoid in which the two transistors on one side of an H-bridge circuit that drives the rotary solenoid are not simultaneously rendered conductive in order to prevent the burning. An instruction signal from the CPU is made up of a first instruction signal which instructs the rotation in either the forward direction or the reverse direction and a second instruction signal which instructs either the rotation or the holding. Depending upon the combinations of the first and second instruction signals, the output of the logic circuit renders the first to fourth transistors of the H-bridge circuit conductive or non-conductive.

Abstract: The present invention relates to an apparatus for diagnosing the presence or absence of a wire disconnection in a fuel injector drive circuit.When driving the solenoid of a fuel injector via a transistor by a drive pulse signal, the counter electromotive voltage used to turn off the transistor during a fall of a drive pulse signal is taken out and is charged to a capacitor included in the charge/discharge circuit. Also, the terminal voltage of the capacitor is determined during the rise of the drive pulse signal, and a wire disconnection is detected when the voltage is lower than a predetermined value. Further, a discharge of capacitor is started immediately after this determination, and a discharge of the capacitor is ended upon the fall of the drive pulse signal.