Abstract: Our overrun prevention ignition system of the capacitor discharge type includes an ignition angle retarding circuit for retarding the ignition angle by an overlapping period between an ignition signal and a predetermined conduction period of a switching transistor associated with an ignition controlling thyristor. The ignition angle retarding circuit includes an ignition signal generating coil sharing a common core with a magneto and includes a capacitor which is charged by a portion of an ignition signal from the ignition signal generating coil. The capacitor discharges for a certain period upon commencement of the decay of the ignition signal to produce a supplemental ignition signal thereby to effectively lengthen the width of the ignition signal. A switching transistor connected to the gate of the ignition controlling thyristor is maintained conductive for a predetermined period of time irrespective of the engine speed to bypass the ignition signal during this period.

Abstract: An ignition system of the capacitor discharge type and capable of preventing overrunning of an internal combustion engine includes a control circuit to render a switching transistor connected to a gate-cathode circuit of a main thyristor conductive for a predetermined period of time to interrupt a backward or reverse phase voltage generated by a magneto and serving as an ignition signal for the main thyristor from being applied thereto. The control circuit includes an integrator circuit connected in parallel with a constant voltage source to develop a voltage increasing with time and includes a voltage divider of the constant voltage source to provide a reference voltage. A transistor circuit of the control circuit compares the output voltage of the integrator circuit and the output voltage of the voltage divider and the transistor circuit maintains a control signal to be applied to the transistor circuit until the output of the integrator circuit reaches the reference voltage of the divider.