Overvoltage and electronic relay circuit for capacitor discharge ignition systems

Claim 2

An ignition system for generating a spark discharge between spaced-apart electrodes in synchronization with an external pulse signal, comprising in combination, an ignition coil having primary and secondary windings, said secondary winding being coupled to the spaced apart electrodes, energy storage means for receiving and storing electrical energy to be discharged into the primary winding of said ignition coil, current control switch means connected to said energy storage means to form a substantially instantaneous low-resistance current path from said energy storage means to the primary winding of said ignition coil to produce a spark discharge between the spaced-apart electrodes in response to the external pulse signal, an energy supply circuit coupled to said energy-storing means to apply electrical energy thereto after each discharge thereof by conduction of said current control switch means, a semiconductor power-switching device having load electrodes and a control electrode, one of said load electrodes connected in circuit with said energy supply circuit to apply power thereto and the other of said load electrodes arranged for connection to an external power source, trigger circuit means connected to the control electrode of said semiconductor power-switching device periodically to render said power-switching device conductive to effect a direct current connection of the external power source to the energy supply circuit after each transfer of energy from said energy storage means into the primary winding of the ignition coil, and a reference voltage device connected in circuit with said trigger circuit means to disable said trigger circuit means and maintain said semiconductor power switching device nonconductive to completely disconnect the external power source from said energy supply circuit when the voltage value of the external power source exceeds a predetermined level.

Claim 3

The ignition system of claim 1 including means coupling the external pulse signal to said trigger circuit means to operate said trigger circuit means in synchronism with said pulse signal information thereby controlling said semiconductor power switching device in a manner to effect direct current connection of an external power source to the energy supply circuit in response to said pulse signal information.

Claim 4

The ignition system of claim 1 wherein said trigger circuit means include first and second current paths, said first current path applying operating potential to said trigger circuit means and said second current path providing a control potential to said trigger circuit means, and said first current path arranged for direct connection to the external power source and said second current path arranged for connection to said external power source through switch means, and a reduction of voltage applied to said second current path substantially instantaneously disabling said trigger circuit means to terminate operation of the ignition system.

Claim 5

The ignition system of claim 1 wherein said semiconductor power switching device is a silicon-controlled rectifier having its load electrodes connected between the external power source and said energy supply circuit, and its control electrode coupled to said trigger circuit means for receiving output signals therefrom to render the silicon-controlled rectifier conductive in response thereto.

Claim 6

The ignition system of claim 4 further including a diode connected in series between said trigger circuit means and the gate electrode of said silicon-controlled rectifier, said diode being biased to allow control signals to flow from said oscillator means to said gate electrode and to block current flow in the opposite direction.

Claim 7

The oscillator circuit of claim 1 wherein said trigger circuit means includes a unijunction transistor having its base electrode forming a first current path to produce control signals therethrough and an emitter electrode connected to a second current path for applying a control potential thereto, and a capacitor connected between said emitter electrode and ground potential for receiving a charge from said external power source, and means coupling a synchronizing pulse from the external pulse signal to said capacitor to add with the charge thereon to rapidly raise the potential thereacross sufficiently to render said unijunction transistor operative to produce an output pulse therefrom in synchronization with said external pulse signal information.

Claim 8

The ignition system of claim 6 wherein said reference voltage device is a zener diode having a zener voltage value greater than the voltage value of the external power source, said zener diode being connected in circuit with said capacitor so that application of an increased voltage above its zener voltage value wilL render the zener diode conductive to disable said unijunction transistor, thereby preventing said power-switching means from connecting the external power source to said energy supply circuit.

Claim 9

The ignition system of claim 6 wherein said first current path to said unijunction transistor is delivered from a direct connection to the external power source, and said second current path for the control potential is delivered through an external switch means, and opening of said switch means causing a reduction in voltage applied to said second current path below said external power source but above zero volts, and the difference of potential between said external power source and the reduced voltage at said second current path acting substantially instantaneously to render said unijunction transistor inoperative to prevent further trigger pulses from being applied to said semiconductor power-switching device.

Claim 10

The ignition system of claim 1 wherein said semiconductor power-switching device is a silicon-controlled rectifier having its load electrodes connected between the external power source and said energy supply circuit, and its control electrode coupled to said trigger circuit means for receiving output signals therefrom to render the silicon-controlled rectifier conductive in response thereto, said trigger circuit means including a unijunction transistor having its base electrodes forming a first current path to produce trigger signals therethrough and an emitter electrode connected to a second current path for applying a control potential thereto, and a capacitor connected between said emitter electrode and ground potential for receiving a charge from said external power source, and means coupling a synchronizing pulse from the external pulse signal information to said capacitor to add with the charge thereon to rapidly raise the potential thereacross sufficient to render said unijunction transistor operative to produce an output trigger pulse therefrom in synchronization with said external pulse signal information: and said reference voltage device having a reference voltage value greater than the voltage value of the external power source, said reference voltage device being connected in circuit with said capacitor so that application of an increased voltage above its reference voltage value will render the reference voltage device conductive to disable said unijunction transistor thereby preventing said semiconductor power-switching means from connecting the external power source to said energy supply circuit when an overvoltage occurs; and said current path to said unijunction transistor is delivered from a direct connection to the external power source, and said second current path for the control potential is delivered through an external switch means, and opening of said switch means will cause a reduction in voltage applied to said second current path below said external power source but above zero volts, and the difference of potential between said external power source and the reduced voltage at said second current path acting substantially instantaneously to render said unijunction transistor inoperative to prevent further trigger pulses from being applied to said semiconductor power-switching device.