Noise immune power switch for automotive accessories

Claim 2

A noise immune electronic switch for powering a utilization device from the cigarette lighter socket of an automotive vehicle having a storage battery, a starter motor and an engine driven alternator system that, during operation, develops an AC ripple voltage having a frequency within a limited frequency range at said lighter socket, comprising: an input connector adapted to mechanically and electrically engage said lighter socket; an output connector adapted for electrical connection to an accessory device; filter means coupled to said input connector for passing signals within said limited frequency range; amplifying means coupled to said filter means for amplifying said signals; switch means connected between said input connector and said output connector; integration means for driving said switch means conductive responsive to a predetermined output from said amplifying means; defeat means for nullifying said integration means when an accessory is connected to said output connector; and turn-on means responsive to a particular signal at said lighter socket for overriding said defeat means to enable said switch means.

Claim 3

The apparatus of claim 1 wherein said integration means is supplied with energy on negative half cycles of said AC ripple voltage only.

Claim 4

The apparatus of claim 2, further including a source of reference voltage and wherein said integration means includes a comparator having one input supplied with said reference voltage.

Claim 5

The apparatus of claim 3, further including a large storage capacitor and wherein said turn-on means includes a transistor having its conduction circuit connected between said storage capacitor and said integration means.

Claim 6

The apparatus of claim 4 wherein said defeating means comprises a diode coupled between said integration means and said output connector.

Claim 7

A noise immune electronic switch for powering an accessory device from the cigarette lighter socket of an automotive vehicle having a storage battery, a starter motor and an engine driven alternator that develops an AC ripple voltage having a frequency within a limited frequency range at said lighter socket comprising: an input connector for making electrical contact with said lighter socket; an output connector for electrically connecting said accessory device; filter means coupled to said input connector for passing said AC ripple voltage; amplifier means coupled to said filter means for amplifying and inverting said AC ripple voltage; normally non-conductive transistor switch means connected between said input connector and said output connector; integration means including an integrating capacitor for developing a voltage responsive to the negative half cycles of said AC ripple voltage from said amplifying means; means for developing a reference potential; comparator means in said integration means having one input supplied with said reference voltage and another input coupled to said integrating capacitor; means connecting the output of said comparator means to said transistor switch means for operating said transistor switch means; diode means for preventing charging of said integrating capacitor by said AC ripple voltage when said transistor switch means is non-conductive and an accessory device is connected to said output socket; a storage capacitor for storing energy; and a turn-on transistor coupled between said storage capacitor and said comparator means for rapidly charging said integrating capacitor and activating said comparator means to operate said transistor switch means in response to a rapid drop in voltage at said input connector upon energization of said starter motor.

Claim 8

A noise immune electronic switch for powering an accessory device from the cigarette lighter socket of an automotive vehicle having a storage battery, a starter motor and an engine driven alternator that develops an AC ripple voltage having a frequency within a limited frequency range at said lighter socket comprising: an input connector for making electrical contact with said lighter socket; an output connector for electrically connecting said accessory device; filter means coupled to said input connector for passing said AC ripple voltage; amplifier means coupled to said filter means for amplifying and inverting said AC ripple voltage; normally non-conductive transistor switch means connected between said input connector and said output connector; integration means including an integrating capacitor for developing a voltage responsive to the negative half cycles of said AC ripple voltage from said amplifying means; means for developing a reference potential; comparator means in said integration means having one input supplied with said reference voltage and another input coupled to said integrating capacitor; means connecting the output of said comparator means to said transistor switch means for operating said transistor switch means; diode means for preventing charging of said integrating capacitor by said AC ripple voltage when said transistor switch means is non-conductive and an accessory device is connected to said output socket; a storage capacitor for storing energy; and a turn-on transistor coupled between said storage capacitor and said comparator means for rapidly charging said integrating capacitor and activating said comparator means to operate said transistor switch means in response to a rapid drop in voltage at said input connector upon energization of said starter motor.