METHODS AND APPARATUS FOR AN IGNITION SYSTEM
Various embodiments of the present technology comprise a method and apparatus for an ignition system. In various embodiments, the ignition system activates a soft shutdown of an ignition coil in the event of an over dwell condition. The apparatus comprises first and second voltage-to-current converters and utilizes a difference of the converter outputs to control the current through the ignition coil. During the soft shutdown, the current decreases non-linearly during a first period and decreases linearly during an immediately following second period.
1 . An igniter capable of controlling an ignition coil, comprising:
a ramp generator configured to generate a ramp voltage; and
a protection circuit coupled to the ramp generator and comprising:
a first voltage-to-current converter coupled to an output terminal of the ramp generator; and
a second voltage-to-current converter coupled to the output terminal of the ramp generator;
wherein an output of each of the first and second voltage-to-current converters are coupled to each other at a reference node.
2 . The igniter according to claim 1 , wherein:
the first voltage-to-current converter is configured to control a first current that decreases a reference voltage at the reference node as the ramp voltage increases; and
the second voltage-to-current converter is configured to control a second current that increases the reference voltage at the reference node as the ramp voltage increases.
3 . The igniter according to claim 2 , wherein the protection circuit is configured to produce a difference signal of the first and second currents at the reference node.
4 . The igniter according to claim 1 , wherein:
the first voltage-to-current converter comprises an inverting input terminal coupled to the output terminal of the ramp generator; and
the second voltage-to-current converter comprises an inverting input terminal coupled to:
the non-inverting input terminal of the first voltage-to-current converter; and
a non-inverting input terminal coupled to the output terminal of the ramp generator.
5 . The igniter according to claim 1 , further comprising a switch element coupled to an output of the protection circuit.
6 . The igniter according to claim 5 , wherein the switch element comprises an insulated-gate bipolar transistor (IGBT), comprising:
a gate terminal coupled to the output of the protection circuit; and
a collector terminal coupled to the ignition coil; and
an emitter terminal coupled to a sense resistor.
7 . The igniter according to claim 6 , wherein the protection circuit is configured to limit a current through the ignition coil according to a voltage at the reference node to produce a soft shut down period, wherein the soft shut down period comprises:
a first period of non-linearly decreasing current; and
a second period, immediately following the first period, of linearly decreasing current.
8 . The igniter according to claim 6 , wherein the protection circuit further comprises a current limiter circuit configured to limit a gate voltage of the IGBT according to a current of the ignition coil.
9 . A method for forming an ignition system having an ignition coil, comprising:
forming an igniter circuit adapted to couple to the ignition coil and capable of:
generating a ramp voltage;
generating a difference signal;
controlling a reference voltage with the difference signal; and
limiting a current through the ignition coil according to the reference voltage to produce a soft shut down period, wherein:
the soft shut down period comprises:
a first period of non-linearly decreasing current; and
a second period, immediately following the first period, of linearly decreasing current.
10 . The method according to claim 9 , wherein limiting the current through the ignition coil comprises reducing a gate voltage to an insulated-gate bipolar transistor (IGBT).
11 . The method according to claim 9 , further comprising limiting a secondary voltage of the ignition coil to a value less than 1000 volts.
12 . The method according to claim 9 , wherein generating the difference signal comprises:
generating a first current output according to the ramp voltage;
generating a second current output according to the ramp voltage; and
subtracting the second current from the first current.
13 . The method according to claim 9 , wherein:
the first current output decreases a reference voltage at a reference node as the ramp voltage increases; and
the second current output increase the reference voltage at the reference node as the ramp voltage increases.
14 . An ignition system, comprising:
an ignition coil; and
an igniter coupled to the ignition coil and comprising:
a ramp generator configured to generate a ramp voltage;
a protection circuit, comprising:
a first voltage-to-current converter coupled to an output terminal of the ramp generator;
a second voltage-to-current converter coupled to the output terminal of the ramp generator; wherein an output of each of the first and second voltage-to-current converters are coupled to each other at a reference node; and
a current limiter circuit coupled to the reference node; and
a switch element coupled to:
an output terminal of the protection circuit; and
the ignition coil.
15 . The ignition system according to claim 14 , wherein:
the first voltage-to-current converter is configured to control a first current that decreases a reference voltage at the reference node as the ramp voltage increases; and
the second voltage-to-current converter is configured to control a second current that increases the reference voltage at the reference node as the ramp voltage increases.
16 . The ignition system according to claim 14 , wherein the switching element comprises an insulated-gate bipolar transistor (IGBT), comprising:
a gate terminal coupled to the output terminal of the current limiter circuit; and
a collector terminal coupled to the ignition coil.
17 . The ignition system according to claim 16 , wherein the protection circuit is configured to limit a secondary voltage of the ignition coil to a value less than 1000 volts.
18 . The ignition system according to claim 14 , wherein the protection circuit is configured to produce a difference signal of the first and second currents at the reference node.
19 . The ignition system according to claim 14 , wherein the switch element is responsive to a feedback loop configured to indicate a magnitude of current though the ignition coil.
20 . The ignition system according to claim 14 , wherein:
the first voltage-to-current converter comprises: an inverting input terminal coupled to the output terminal of the ramp generator; and
the second voltage-to-current converter comprises:
an inverting input terminal coupled to the non-inverting input terminal of the first voltage-to-current converter; and
a non-inverting input terminal coupled to the output terminal of the ramp generator.