US Patent 10536991 Bi-polar triac short detection and safety circuit

Disclosed is a safety circuit for disrupting power to a heating element of an appliance to be powered through a solid state switch (Q1), typically a triac, from an AC power source (V1) having a positive half cycle and a negative half cycle for delivering power. A low resistance condition is sensed by detecting either the current through, or voltage across, the solid state switch during the positive half cycle and the negative half cycle of the AC power line, when the solid state AC switch is not actuated. A fault signal is generated to interrupt power to the heating element, preferably by a crowbar circuit opening a fuse, whenever the low resistance condition is detected.