Alternating current capacitor discharge ignition system

Claim 1

In a capacitor discharge ignition system for an internal combustion engine having an ignition capacitor, trigger means for discharging said ignition capacitor in synchronism with the engine to produce ignition pulses, a semiconductor controlled rectifier having a gate, an anode and a cathode, a power transistor for charging said ignition capacitor, said power transistor having control and output electrodes, a transformer having first, second and third inductively coupled windings with the output electrode of said power transistor being coupled to said first winding, circuit means for connecting said second winding to said control electrode of said power transistor with increasing current in said first winding increasing current in said second winding and driving said power transistor into saturation with said ignition capacitor being charged, a first diode and said third winding connected in series and coupled across said ignition capacitor with pulses of one polarity induced in said third winding charging said ignition capacitor, an enabling transistor having control and output electrodes with said control electrode being coupled to said anode of said semiconductor controlled rectifier for activating said transistor, a high voltage transformer having primary and secondary windings and being connected to said cathode of said semiconductor controlled rectifier, a capacitor coupled between said output of said enabling transistor and said control electrode of said power transistor for initiating said power transistor with said enabling transistor being activated, a supply potential coupled to said power and enabling transistors, a zener diode connected between said output electrode of said enabling transistor and a reference potential and poled to prevent changes in magnitude of said supply potential from initiating said power transistor, first diode means coupled between said ignition capacitor and said anode of said semiconductor controlled rectifier for preventing said ignition capacitor from delaying the activation of said power transistor, a capacitor connected between said input of said semiconductor controlled rectifier and said reference potential to filter out turnoff spikes resulting from said power transistor becoming saturated, said filter preventing damage to said semiconductor controlled rectifier, the combination including second diode means coupled between said output of said semiconductor controlled rectifier and said ignition capacitor and poled to create a ringout oscillation between said ignition capacitor and said high voltage transformer thereby causing an alternating current to appear across the spark gap.