Protector circuit for solenoid operator

Claim 1

Switching apparatus including an interrupter section comprising main contact means for series connection in a load circuit, a spring powered mechanism connected to said main contact means, electrically powered operator means connected to said mechanism for selectively operating the latter to open and close said main contact means, and protector means to prevent burnout of said operator means; said protector means including a solid state unit having power electrode means connected in series with said operator means in an energizing circuit for said operator means, and control electrode means to regulate current flow in said energizing circuit; said protector means also including a control circuit in series with a portion of said energizing circuit and controlling the potential at said electrode means; said control circuit including impedance means for controlling the potential applied to said control electrode means; said impedance having a relatively sharp temperature impedance characteristic coordinated with the energy withstand characteristic of the operator means whereby current flowing in said energizing circuit will raise said element to a switching temperature before said operator means is damaged by overheating; at said switching temperature said impedance means having an impedance level such that the potential applied by said control circuit to said control electrode means drives said solid state unit into a blocking state thereby interrupting said energizing circuit to deenergize said operator means.