Control circuit for fast heating of a positive-temperature-coefficient heating component

A heating control circuit comprising:

• a circuit power supply input for receiving a direct current;
• a heater power supply input for receiving an alternating current;
• comparator means for comparing a sensing voltage on a first input to a reference voltage on a second input to generate a compare output;
• voltage generator means, coupled to the circuit power supply input, for generating a first reference voltage and a second reference voltage;
• sensing switch means for connecting the first reference voltage to the second input of the comparator means in response to a heat-up signal being in a first state, and for connecting the second reference voltage to the second input of the comparator means in response to the heat-up signal being in a second state;
• temperature setting selector means for detecting power through a heating element, for generating the heat-up signal in the first state when power detected is above a threshold power, and for generating the heat-up signal in the second state when power detected is below the threshold power;
• temperature-sampling switch means, coupled between the heating element and the comparator means, for disconnecting the heating element from the first input of the comparator means when the heating element is being heated, and for connecting the heating element to the first input of the comparator means when the heating element is being sensed for temperature measurement;
• silicon-controlled rectifier (SCR) means, coupled between the heater power supply input and the heating element, for disconnecting the heater power supply input from the heating element when the heating element is being sensed for temperature measurement, the SCR means having a trigger input for controlling activation of the SCR means;
• and
• trigger circuit means, receiving the compare output from the comparator means, for generating a trigger signal applied to the trigger input of the SCR means.

A temperature-control product comprising:

• a heating body having a positive temperature coefficient;
• a heater power supply for powering the heating body;
• a silicon-controlled rectifier (SCR) coupled between the heater power supply and the heating body, the SCR disconnecting the heater power supply from the heating body during a temperature-sensing time period, the SCR having a trigger input;
• a comparator for comparing a sensing voltage on a first input to a reference voltage on a second input to generate an output signal indicating a temperature of the heating body;
• a sensing power supply;
• an isolation device coupled between the first input of the comparator and the heating body to supply a sensing current into the heating body during the temperature-sensing time period;
• a voltage generator coupled to the sensing power supply, the voltage generator generating a first reference voltage and a second reference voltage;
• a sensing switch that selects the first reference voltage or the second reference voltage to apply to the second input of the comparator in response to a heating-up signal;
• and
• a temperature setting selector, coupled to the trigger input of the SCR, for generating the heating-up signal in an activated state when power through the SCR to the heating body is above a threshold power,
• whereby temperature settings that correspond to reference voltages are selected in response to power above the threshold power.