An improved trigger circuit for a magneto-type ignition system is described. The trigger circuit includes a first generating coil for supplying current flow to a primary winding of the ignition coil, a transistor for controlling the current flow through the primary winding, a capacitor, a thyristor for cooperating with the capacitor to render the transistor non-conductive, and a second generating coil for supplying the power required to charge the capacitor and to control the conduction of both the transistor and thyristor, such that the capacitor is charged and the transistor is rendered conductive by one half wave output from the second generating coil and the thyristor is rendered conductive by the other half wave output from the second generating coil. The conduction of the thyristor is operative to discharge the capacitor and render the transistor non-conductive, whereby the current flow from the first generating coil is directed through the primary winding of the ignition coil to induce a sparking potential in the secondary winding of the ignition coil.