Abstract: A safety circuit to disrupt power to a heating element of an appliance to be powered through a solid state switch (Tri-ac, Q1), typically a triac, from an AC power source (V1) having a positive half cycle and a negative half cycle 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.

Abstract: A dual heater wire circuit for use with a heating pad or electric blanket includes two independent heater wire circuits. Each heater wire circuit includes a heater wire and a temperature sensor conductor. The temperature sensor conductor of each heater wire circuit is connected to a capacitor, or to a resistor, to define with the capacitor or resistor a voltage divider circuit. The juncture between the sensor conductors and either the capacitor or the resistor is provided to the input of a microprocessor. The electrical resistance of the temperature sensor conductors varies with temperature. The signal provided to the microprocessor from the voltage dividers formed between the sensor conductors of the heater wires and either the capacitor or resistor will vary in phase or voltage relative to the temperature of the heater wires. The microprocessor controls the duty cycle of the power signal provided to the heater wires.

Abstract: A safety circuit to disrupt power to a heating element of an appliance to be powered through a solid state switch (Tri-ac Q1), typically a triac, from an AC power source (V1) having a positive half cycle and a negative half cycle 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.

Abstract: A safety overheat protection circuit for flexible heater wire used in heating pads and electric blankets. The heater wire includes a low melt temperature fuse-able layer and a conductive core. A polymetric positive temperature coefficient (PPTC) device is used in series with the heater wire in a configuration so that a hot spot anywhere along the length of the wire will cause the fuse-able layer to melt and the heater wire to short to the conductive core, increasing the current and causing the PPTC device to change to a high impedance state significantly removing power to the heater wire. In addition, dual circuits having the same operating target temperature are presented as a safe method of temperature control.

Abstract: Methods and system for controlling a heater conductor in a heating element including a sensor conductor separated from the heater conductor by an NTC layer. The heating element is coupled to a control circuit and the flow of electricity from a direct current source through the circuit is controlled such that a change of the resistance of the NTC layer is indicative of the temperature of the heater conductor. This resistance is detected based on a time or amplitude analysis and based thereon, a heating mode of the heater conductor is controlled. In a variation, the circuit is operated in a two-period measurement mode wherein the energy transferred through the NTC layer in one period is equal and opposite to the energy transferred through the NTC layer in the other period.

Abstract: Methods and system for controlling a heater conductor in a heating element including a sensor conductor separated from the heater conductor by an NTC layer. The heating element is coupled to a control circuit and the flow of electricity from a direct current source through the circuit is controlled such that a change of the resistance of the NTC layer is indicative of the temperature of the heater conductor. This resistance is detected based on a time or amplitude analysis and based thereon, a heating mode of the heater conductor is controlled. In a variation, the circuit is operated in a two-period measurement mode wherein the energy transferred through the NTC layer in one period is equal and opposite to the energy transferred through the NTC layer in the other period.

Abstract: An improved control device and method is usable with flexible heating wire having a conductive core with a Negative Temperature Coefficient (NTC) layer and a helically wound heater conductor within an insulative outer sheath. The conductive core is coupled to a control circuit, a phase shift relative to the AC power supply being indicative of the temperature of the wire. The nonlinear nature of the NTC layer enhances the detection of local hot spots anywhere along the length of the wire. Precise temperature measurement is achieved by measuring the time differences between two zero crossings and the power to the heater compensates for abnormal use such as bunching of the heater wire. The control of the heater wire is particularly suitable for use with appliances such as heating pads and electric blankets.