Ignition control device and reference voltage adjustment method of ignition control device
To provide an ignition control device of an internal combustion engine capable of reducing the number of adjustment steps required for adjustment such as matching of a MOS gate voltage or the like without being affected by device variation. A detection voltage is generated on the basis of a primary current flowing through a current detection resistor having a positive temperature dependent characteristic. A reference voltage is generated by a potential difference between a base and an emitter of a first bipolar transistor circuit and a multiple type second bipolar transistor circuit in which a plurality of bipolar transistors are connected in parallel, and a resistance value of a first resistor connected to the emitter side of the plurality of the bipolar transistor circuit, on the basis of a current having a positive temperature dependent characteristic similar to the current detection resistor.
1. An ignition controller that drives a switch for controlling a current flowing through a primary side coil of an ignition coil, the ignition controller comprising a current limiter configured to control the switch to limit the current flowing through the primary side coil when a detection voltage exceeds a reference voltage, the current limiter including:
a detection voltage generator that generates the detection voltage corresponding to a primary current flowing through the primary side coil,
a reference voltage generator that generates the reference voltage corresponding to a reference current, the reference voltage generator comprising:
a current mirror circuit;
a first bipolar transistor circuit having a collector side connected to a current source;
a multiple type second bipolar transistor circuit including:
a larger number of bipolar transistors than the first bipolar transistor circuit,
a collector side connected to one side of the current mirror circuit, and
a base side connected to a base side of the first bipolar transistor circuit;
a Widlar constant current circuit consisting of a first resistor connected to an emitter side of the multiple type second bipolar transistor circuit; and
a second resistor connected to another side of the current mirror circuit,
wherein the first bipolar transistor circuit includes at least one bipolar transistor that is the same as a bipolar transistor of the multiple type second bipolar transistor circuit,
wherein the ignition controller is configured to adjust a plurality of characteristics to be set for the reference voltage generator to output the reference voltage, the plurality of characteristics including:
a number of bipolar transistors including the first bipolar transistor circuit and the multiple type second bipolar transistor circuit,
a mirror ratio of the current mirror circuit, and
a resistance ratio between the first resistor and the second resistor,
wherein the reference voltage has a temperature dependent characteristic falling within a predetermined error range with respect to a temperature dependent characteristic of the current detection resistor,
a comparator configured to compare a magnitude relationship between the detection voltage and the reference voltage,
wherein the detection voltage is generated in the detection voltage generation unit on the basis of the primary current flowing through a current detection resistor having a positive temperature dependent characteristic formed of a metal material,
wherein the reference voltage is generated by all of:
a potential difference proportional to a thermal voltage VT, the potential difference being between a base and an emitter of a first bipolar transistor circuit;
the potential difference between a base and an emitter of a multiple type second bipolar transistor circuit, wherein a plurality of bipolar transistors are connected in parallel in the multiple type second bipolar transistor circuit; and
a resistance value of a first resistor connected to the emitter side of the multiple type second bipolar transistor circuit,
wherein the reference voltage is generated in the reference voltage generator on the basis of a current having a positive temperature dependent characteristic similar to the current detection resistor; and
wherein a positive temperature coefficient of the detection voltage by the current detection resistor is about 4×10 −3 /° C., and a positive temperature coefficient of the reference voltage of the reference voltage generator is about 3.3×10 −3 /° C.
2. The ignition controller according to claim 1 , further comprising:
a level shifter configured to adjust the level of the reference voltage from the reference voltage generator, the level shifter provided between the reference voltage generator and the comparator.
3. A reference voltage adjustment method of an ignition controller that drives a switch for controlling a current flowing through a primary side coil of an ignition coil, the ignition controller comprising a current limiter configured to control the switch to limit a current flowing through the primary side coil when a detection voltage exceeds a reference voltage, the current limiter including:
a detection voltage generator that generates the detection voltage corresponding to a primary current flowing through the primary side coil detected by a current detection resistor made of a metal,
a reference voltage generator that generates the reference voltage corresponding to a reference current, and
a comparator configured to compare a magnitude relationship between the detection voltage and the reference voltage,
wherein the reference voltage generator includes:
a current mirror circuit,
a first bipolar transistor circuit having a collector side connected to a current source,
a multiple type second bipolar transistor circuit including:
a larger number of bipolar transistors than the first bipolar transistor circuit,
a collector side connected to one side of the current mirror circuit, and
a base side connected to a base side of the first bipolar transistor circuit,
a Widlar constant current circuit consisting of a first resistor connected to the emitter side of the multiple type second bipolar transistor circuit, and
a second resistor connected to another side of the current mirror circuit,
wherein the first bipolar transistor circuit includes at least one bipolar transistor that is the same as a bipolar transistor of the multiple type second bipolar transistor circuit,
wherein the ignition controller is configured to adjust at least one of a plurality of characteristics for the reference voltage generator to output the reference voltage, the plurality of characteristics being at least one of:
the number of the bipolar transistors composing the first bipolar transistor circuit and the multiple type second bipolar transistor circuit,
a mirror ratio of the current mirror circuit, and
a resistance ratio between the first resistor and the second resistor,
wherein the reference voltage has a temperature dependent characteristic falling within a predetermined error range with respect to a positive temperature dependent characteristic of the current detection resistor,
wherein the current detection resistor is made of a metal, and
wherein a positive temperature coefficient of the detection voltage by the current detection resistor is about 4×10 −3 /° C., and a positive temperature coefficient of the reference voltage of the reference voltage generator is about 3.3×10 −3 /° C.