Switch control apparatus for eliminating intermittent on/off condition on a power supply switch

Claim 1

In a power system including a solenoid switch connecting a power supply to a load, an apparatus for controlling the on/off of the solenoid switch, comprising: voltage magnitude detection means, coupled to the power supply, for defining three voltage levels V1, V2, and V3, and a corresponding four voltage ranges, a first range below V1, a second range between V1 and V2, a third range between V2 and V3, and a fourth range above V3, and for detecting a voltage magnitude of the power supply; logic means, coupled to said voltage magnitude detection means, for responding to a change in said power supply voltage magnitude, and for registering a change in said power supply voltage magnitude from one of said voltage ranges to another; and switch control means, coupled to said voltage magnitude detection means and said logic means, for controlling the on/off of the solenoid switch, wherein, (a) the solenoid switch is off when said power supply voltage magnitude is within said first range, (b) the solenoid switch is off when said power supply voltage magnitude changes from said first to said second range and remains off in said second range, (c) the solenoid switch turns on when said power supply voltage magnitude changes from said second range to said third range, and remains on in said third range; and (d) the solenoid switch is on when said power supply voltage magnitude changes from said third range to said second range, and remains on in said second range.