Circuit and method for controlling a coil current during a soft shut down
AssigneeSemiconductor Components Industries, LLC
InventorYasuhiro Nodake
Life of this patent
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Abstract
A current control circuit for an ignition system (i.e., igniter current limiter) is disclosed. The current control circuit can reduce a coil current over a soft shut down (SSD) period using an insulated gate bipolar transistor (IGBT) that is controlled by a negative feedback loop, which controls the current limit of the IGBT according to a SSD profile. In order to prevent an unwanted current rise during the soft shut down period, the current control circuit compares a gate voltage of the IGBT to a reference signal and based on the comparison can enable the SSD profile to include a fast ramp. The fast ramp quickly lowers the current limit of the IGBT so that the coil current equals the current limit and can be controlled by the negative feedback loop.
Claims20
A system for controlling a current in a coil, the system comprising:
- a coil;
- a transistor coupled to the coil, the transistor configured to conduct a coil current of the coil that is at or below a current limit of the transistor;
- and
- a control circuit coupled to the transistor, the control circuit configured to discharge the coil by controlling the transistor to reduce the coil current by reducing the current limit of the transistor according to a fast ramp profile when the coil current is not equal to the current limit of the transistor and according to a slow ramp profile when the coil current is equal to the current limit of the transistor.
A method for controlling a current in a coil, the method comprising:
- controlling a transistor coupled to a coil to conduct a coil current that is at or below a current limit of the transistor;
- and
- discharging the coil, wherein the discharging includes:
- determining that the coil current is not equal to the current limit of the transistor;
- reducing the current limit of the transistor according to a fast ramp profile to reduce the coil current;
- determining that the coil current is equal to the current limit of the transistor;
- and
- reducing the current limit of the transistor according to a slow ramp profile to reduce the coil current.
Dependencies are inferred from the claim text.