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 coil current control circuit comprising:
- a transistor in series with a coil, the transistor controllable to conduct current at or below a coil current limit;
- a current sensing circuit configured to sense a coil current flowing through the transistor;
- and
- a current limit control circuit configured to compare a voltage from the current sensing circuit to a soft shut down (SSD) signal from a ramp generator circuit, and based on the comparison, control the coil current limit of the transistor to reduce the coil current over a SSD period according to a profile of the SSD signal, the profile of SSD signal being based on a gate voltage of the transistor.
A system comprising:
- a coil;
- an insulated gate bipolar transistor (IGBT) coupled to the coil, the IGBT configured to conduct a coil current of the ignition coil that is at or below a current limit;
- and
- a current limit control circuit coupled in a feedback loop with the IGBT, the current limit control circuit configured to control the IGBT to reduce the current limit according to a fast ramp profile when the coil current is below the current limit and according to a slow ramp profile when the coil current is at the current limit.
(canceled)
A circuit for reducing a coil current of a coil, the the circuit configured to:
- determine that the coil current is below a current limit of a transistor coupled to the coil;
- reduce the current limit of the transistor according to a fast ramp profile to reduce the coil current of the coil;
- determine that the coil current as at the current limit of the transistor;
- and
- reduce the current limit of the transistor according to a slow ramp profile to further reduce the coil current of the coil until the coil is discharged.
Dependencies are inferred from the claim text.