Ignition coil driver device with slew-rate limited dwell turn-on
View Patent ↗A device to control the charging rate of an ignition coil for an internal combustion spark ignition engine. The device controls the turn-on rate of the primary coil by slew-rate limiting using switching devices and a Miller-effect capacitor in order to reduce secondary oscillation magnitudes originated by a sharp transition of the controlling switch.
1. A circuit for driving an ignition coil, the circuit comprising:
a switching portion in electrical communication with the ignition coil for providing a current path; and
a rate limiting portion in electrical communication with the switching circuit, the rate limiting portion being configured to control a voltage transition time as the switching portion transitions from a non-conducting mode to a fully conducting mode, wherein the switching portion includes:
a first transistor connected in electrical series with the ignition coil;
a second transistor connected to the control input of the first transistor;
a capacitor connected in electrical series between the switched side of the ignition coil and the control input of the second transistor; and
a diode connected in series between the control input of the second transistor and the capacitor to isolate the control input of the second transistor from the capacitor as the first transistor transitions from a fully conducting to a non-conducting mode.
2. The circuit according to claim 1 , further comprising, a second diode and a resistor, the second diode being connected between a control input of the first transistor and the ignition coil, and the resistor is connected between the control input of the first transistor and a voltage reference.
3. The circuit according to claim 1 , wherein a resistor and a second diode are in electrical communication with the capacitor to provide a discharge path for the capacitor after first transistor transitions to a non-conducting mode.
4. A circuit for driving an ignition coil, the circuit comprising:
a first transistor connected in electrical series with the ignition coil;
a second transistor connected to a controlled input of the first transistor; a capacitor connected between an output of the first transistor and a control input of the second transistor, wherein the first transistor is connected to the ignition coil and a first side of the capacitor; and
a diode connected in series between a second side of the capacitor and the control input of the second transistor.
5. The circuit according to claim 4 , wherein the second transistor is configured to amplify the capacitive effect of the capacitor while the first transistor operates in a linear region.
6. The circuit according to claim 4 , further comprising a second diode and a resistor, the second diode and the resistor being connected between the capacitor and a reference voltage to discharge the capacitor.
7. The circuit according to claim 4 , wherein the diode is connected between the ignition coil and a control input of the first transistor.
8. The circuit according to claim 7 ,wherein a resistor is connected between the control input of the first transistor and a voltage reference.
9. The circuit according to claim 4 , wherein the first transistor is configured to create a voltage at the ignition coil based on a time constant τ where τ=R*Cm, while the first transistor operates in a cutoff region, where R is the resistance of the resistor, and Cm is the capacitance of the capacitor.
10. The circuit according to claim 4 , wherein the first transistor is configured to provide a voltage to the ignition coil based on a time constant τ where τ=R*Cm*[1+K], while the first transistor operates in a linear region, where R is the resistance of the resistor, Cm is the capacitance of the capacitor, and K is the inverting gain provided by the first and second transistor.
11. The circuit according to claim 4 , wherein the first transistor is configured to provide a voltage to the ignition coil based on a time constant τ where τ=R*Cm, while the first transistor operates in a saturation region where R is the resistance of the resistor, and Cm is the capacitance of the capacitor.