US 2009/0015316 A1 · Heating-Control Isolation-Diode Temperature-Compensation

Abstract

A semiconductor integrated circuit (IC) acts as a controller of a heating-controlled device or appliance. A heating body has a positive temperature coefficient and acts as both a heating element and a temperature sensor. A Silicon-Controlled Rectifier (SCR) switches AC current to the heating body to increase its temperature. When the SCR switches off, temperature sensing is performed using a sampling resistor, isolation diode, voltage comparator, and switch for a low-voltage DC supply are formed on an integrated circuit that has a first circuit branch and a second circuit branch. A compensation diode and a compensation resistor can be added in parallel to reference resistors. The compensation diode compensates for the forward voltage drop of the isolation diode that would otherwise create an inaccurate temperature measurement. The diodes have the same temperature response, allowing for a more accurate temperature measurement over a full temperature range of the sensorless appliance.

Claims20

Dependent claims

A temperature-sensing circuit comprising:

a comparator that receives a sensing voltage and a reference voltage and generates a compare output;
a voltage divider between a power supply and a compensation node, the voltage divider generating the reference voltage applied to the comparator;
a sensing branch that senses a sensing current through a heating body to generate the sensing voltage;
an isolation diode in the sensing branch to protect the comparator from damage due to high voltages;
a sampling resistor in the sensing branch, the sampling resistor limiting the sensing current;
a compensation branch between the power supply and a ground;
a compensation diode in the compensation branch, the compensation diode for compensating the sensing voltage applied to the comparator for a voltage drop through the isolation diode;
and
a compensation resistor in the compensation branch to supply current to the compensation diode;
wherein the compensation node of the voltage divider is a terminal of the compensation diode,
whereby the compensation diode adjusts the reference voltage applied to the comparator by the voltage divider to compensate for the voltage drop through the isolation diode.

8 more elements

A heating control circuit comprising:

voltage compare means for comparing a sense voltage to a reference voltage to generate an output signal that indicates a temperature of a heating body that also acts as a temperature sensor;
voltage divider means for generating the reference voltage from a power supply voltage;
sampling resistor means for limiting a sensing current from the power supply voltage;
isolation diode means for preventing back current flow from the heating body to the voltage compare means, the isolation diode means generating a rectifier voltage drop as the sensing current passes through the isolation diode means;
wherein the sampling resistor means and the isolation diode means are connected in series between the power supply voltage and the heating body to generate the sense voltage;
compensation resistor means for limiting a compensation current from the power supply voltage;
and
compensation diode means for generating a compensating voltage drop when the compensation current passes through the compensation diode means;
wherein the compensation resistor means and the compensation diode means are connected in series, with a compensation node in between;
wherein the voltage divider means is connected between the power supply voltage and the compensation node, wherein the reference voltage to the voltage compare means is compensated by the compensation diode means to compensate for the isolation diode means,
whereby the rectifier voltage drop is compensated for.

8 more elements

A sensorless heating appliance comprising:

a heating body having a positive temperature coefficient;
a heater power supply;
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;
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;
a sampling resistor coupled to the sensing power supply and to the first input of the comparator;
an isolation diode 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 compensation diode coupled between a compensation node and a ground;
and
a compensation resistor coupled between the compensation node and the sensing power supply,
whereby the compensation diode compensates for a voltage drop through the isolation diode.

8 more elements

Dependencies are inferred from the claim text.

Heating-Control Isolation-Diode Temperature-Compensation

Life of this patent

Heating-Control Isolation-Diode Temperature-Compensation

Life of this patent

Abstract

Claims20