Circuit and method for coil current control
AssigneeSemiconductor Components Industries, LLC
InventorMikio Yamagishi
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Abstract
Circuits and methods to control a current in a coil are disclosed. The circuit and methods provide over-dwell protection and soft shut-down functionality to safely discharge the coil. The safe discharge of the coil is facilitated by a soft-start ramp signal that reduces the coil current gradually by controlling a switching device according. A profile of the soft-start ramp signal over time determines the gradual reduction. The profile of the soft-start ramp signal can be adjusted to set (i) an over-dwell period of the coil current, after which the coil current is shut down, and (ii) a soft shut-down period, over which the coil current is gradually reduced.
Claims20
A circuit for controlling a current in a coil, the circuit comprising:
- a capacitor connected between a voltage source (VS) and an output node;
- a first switching device connected between the voltage source and the output node such that when the first switching device is in an ON state the output node is coupled to the voltage source, and when the first switching device is in an OFF state the output node is coupled to the voltage source through the capacitor;
- and
- a voltage-controlled current-source (VCCS) connected between the output node and a ground, the VCCS outputting a current that charges the capacitor such that when the first switching device is moved from the ON state to the OFF state, a voltage is generated at the output node that decreases over a period from VS to a ground voltage according to a soft-start-profile.
A method for controlling a current in a coil, the method comprising:
- receiving a charge coil trigger signal
- generating a soft-start ramp signal that has a voltage profile that decreases with time;
- and
- applying the soft-start ramp signal to a gate of a switching device to gradually shut down the current in the coil over a soft shut-down period after an over-dwell period, wherein the soft shut-down period and the over-dwell period correspond to the voltage profile of the soft-start ramp signal.
A soft-start ramp generator, comprising:
- a voltage source terminal;
- a ground terminal;
- an output node;
- a capacitor coupled between the voltage source terminal and the output node;
- and
- a voltage controlled current source (VCCS) coupled between the output node and the ground terminal, the VCCS configured to control a current through the capacitor based on a voltage across the capacitor so that a voltage at the output node decreases from a voltage at the voltage source terminal to a voltage at the ground terminal according to a soft-start profile.
Dependencies are inferred from the claim text.