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Compensated dual injector driver

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TLDR
In this paper, a compensated dual injector driver circuit for controlling the current to either of a pair of electromagnetic solenoid fuel injectors is described, where the driver amplifier in response to the leading edge of a control pulse regulates the conductance of the selected transistor with the current control signal to initially draw current through the injector coil until it reaches a peak value.
Abstract
A compensated dual injector driver circuit for controlling the current to either of a pair of electromagnetic solenoid fuel injectors is disclosed. The driver circuit includes a pair of analog bilateral switches operably connected to the control terminals of two driver transistors whose power terminals are coupled serially with the coils of the injector solenoids. A driver amplifier generating a current control signal for the driver transistors is connected to a common input of the two switches. Either of the switches is selected for closure by a logical input from a select line thereby choosing the individual injector to be energized. The driver amplifier in response to the leading edge of a control pulse regulates the conductance of the selected transistor with the current control signal to initially draw current through the injector coil until it reaches a peak value. At the time the peak current is attained, the driver amplifier then switches the control current to a holding value. The peak and the holding current levels are measured by a negative feedback loop from a sense resistor commonly connected in series with each set of coils and driver transistors to indicate the magnitude of current therethrough. The circuit further includes a means for controllably collapsing the magnetic field stored in the injector coils when the injector driver transistors are turned off in response to the trailing edge of the control pulse. Compensation is provided to the driver amplifier for altering the hold level current in accordance with variations in the battery voltage. The differing levels of hold current with changing battery voltage will modify the closing time of the injector oppositely to those changes produced in the opening times by the battery voltage.

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Citations
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References
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Apparatus for controlling the operating current of electromagnetic devices

TL;DR: In this article, the valve actuating current is sensed by a suitable transducer, for example a resistor, and the resulting signal is fed to a two-point controller which suitably alters the input to the driver circuit to change the valve actuating current.
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Regulating arrangement for solenoid valves and the like

TL;DR: In this paper, the authors propose an arrangement for regulating the current flow in the solenoid of an electromagnetically actuated mechanism, particularly a high-speed valve, of the type requiring a higher activating current to effect movement of the armature from a first to a second position and a lower holding current to maintain the armatures in such second position.
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Fuel injector driver circuit

TL;DR: In this paper, a circuit is described for energizing an electromagnetically operated fuel injector from an unregulated voltage source in response to an injection command pulse, which is provided by directly coupling the unregulated voltage across the injector upon the initiation of the injection command pulses.
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An apparatus for controlling an electromagnetic valve

TL;DR: In this article, an apparatus for controlling an electromagnetic valve which is adapted for use with the fuel injection systems of internal combustion engines is described, and after the expiration of a predetermined time the control of the energization of the electromagnetic coil of the valve is changed from constant-voltage control to constant-current control, and any surge voltage caused during the control change is selectively absorbed, thereby ensuring stable energization despite variations in the supply voltage or the like.
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Driver circuit for printer electromagnet

TL;DR: In this paper, a circuit for energizing the electromagnet of the print head of a high speed impact printer was proposed, which operates effectively with an unregulated supply voltage by providing energization current pulses whose level and duration are dependent on the present level of such supply voltage.