Process and a circuit arrangement for the control of the primary current in coil ignition systems of motor vehicles

A circuit arrangement for controlling the current through the primary winding of an ignition coil of a motor vehicle in response to the open and closed time intervals of a cyclically operating points circuit and substantially independent of engine speed, supply voltage and the internal resistance of the ignition coil, comprising:

• a capacitor;
• a first constant current source connected to said capacitor and for connection to the points circuit and operable to charge said capacitor in response to the open time interval condition of the points circuit;
• a second constant current source connected to said capacitor and for connection to the points circuit and operable to discharge said capacitor in response to the closed time interval condition of the points circuit;
• a capacitor connected to said capacitor and operable to produce a first signal in response to the voltage across said capacitor falling below a predetermined value;
• an AND gate connected to said comparator and for connection to the points circuit and operable to produce a second signal in response to said first signal in conjunction with the closed time interval condition of the points circuit;
• transistor means including an emitter circuit connected to a reference potential by way of said resistor, a collector circuit for connection to the supply voltage by way of the primary winding, and a base circuit connected to said AND gate, said transistor activated in response to said second signal to cause current to flow in series through said resistor and the primary winding;
• a current limiting circuit connected to said resistor and said base circuit to hold said second signal constant in response to the voltage across said resistor reaching a predetermined value;
• voltage divider means including a plurality of taps for providing predetermined voltage values,
• and wherein each of said first and second constant current sources comprises
• an operational amplifier having an inverting input, a non-inverting input and an output, said non-inverting input connected to a respective tap,
• a first transistor having a base-emitter circuit connected between said output and said inverting input and a collector circuit connected to said capacitor, and
• a second transistor including an emitter circuit connected to an operating voltage, a collector circuit connected to said input, and a base circuit for connection to a points circuit for controlling activation and deactivation of the constant current source.