Over-voltage protected solid-state ignition system

Claim 1

Over-voltage protected ignition system for an internal combustion engine, for connection to a source of power (1) and to a source of ignition signals (20-23) having an ignition coil (9); a power transistor (10) serially connected to the source of power and the ignition coil; and a control circuit including a control transistor (16) which, in turn, controls the switching state of the power transistor, the control circuit being connected to cause the control transistor to be in conductive state when the power transistor is blocked, and vice-versa, and a base circuit (17-19) connected to said control transistor (16) and controlled by said source of ignition signals; and comprising a power source over-voltage monitoring circuit (24) sensing when the voltage of the source reaches a value which would cause excessive current flow through the power transistor (10) and connected to the control transistor (16) to apply a voltage to the control transistor which causes the control transistor to assume non-conductive state, including a breakdown circuit element (25) abruptly changing its state of current conduction upon occurrence of a threshold voltage condition, the breakdown element (25) being serially connected to the base-emitter path of the control transistor (16) and providing an over-voltage conduction signal thereto; a dropping protective resistor (7) having one terminal connected to the power source; a parallel circuit network formed by the control circuit for the power transistor (10) and the over-voltage monitoring circuit (24) one end point of the parallel circuit network being connected to the control electrode of the power transistor (13), the other end point of the parallel circuit network being connected to the terminal of said dropping protective resistor (7) remote from the power source, so that the dropping protector resistor will form a common dropping resistor for the branches of said parallel circuit network; and a capacitor (28) which provides, upon occurrence of an over-voltage condition, for gradual application of the over-voltage signal to the control transistor to control said control transistor (16) to become conductive gradually, thus causing disconnection of the power transistor (10) and inhibiting generation of a spurious ignition event and spurious response upon presence of noise pulses, while providing for reliably decreased reduction of the power transistor upon excessive over-voltage of the source.