Patent ID: 8461844

Claim:
A self charging ion current sensing circuit for use with a spark control circuit for generating sparking current across a spark gap of a spark plug, comprising: an ion bias capacitor coupled in series with the spark control circuit, the ion bias capacitor including a Zener diode clamp coupled thereto and parallel therewith to limit a voltage build up on the ion bias capacitor during a sparking event; an ion Zener diode having a cathode coupled to the anode of the Zener diode clamp and an anode coupled to ground; an offset circuit having an input coupled between the Zener diode clamp and the ion Zener diode, the offset circuitry generating a positive voltage in response to an ion current flow; and a buffer and amplifier circuit coupled to the offset circuitry to provide a zero to five volt DC output depending on a type of current flow in the spark control circuit, whereby the output from the buffer and amplifier circuit is approximately one volt when there is no current flowing in the spark control circuit, whereby the output is approximately zero volts when there is cathode spark current flowing in the spark control circuitry, and wherein the output of the buffer and amplifier circuit ranges between approximately one and five volts in proportion to a magnitude of ion current flowing through the spark gap, wherein the output from the buffer and amplifier circuit provides an indication of particular modes of spark plug operation.