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Fig. 1 shows two example circuits for the IC temperature sensor. Notice that the symbol for this device is two interlocking circles with a + and - used to indicate polarity. This type of sensor changes the amount of voltage across its PN junction as the temperature of the junction changes. In the first circuit, a bias voltage is applied to the circuit and a variable resistance is used to provide a setpoint. As the temperature changes, the amount of current will change proportionally because the voltage across the PN junction of the IC will change. This can provide very accurate temperature readings between -55°C - 150°C. The IC sensor can be used on printed circuit boards to monitor the temperature of the heat sink or it can be integrated into a cold-junction compensation circuit for a thermocouple.
The second circuit shows two IC temperature sensors used with an op amp. The first IC is used as a temperature sensor and the second is used to provide temperature compensation for the circuit. One may troubleshoot the IC temperature sensor while it's in circuit. The amount of voltage through the PN junction should change as the IC temperature is changed. If the IC is used in a circuit where this voltage change provides a voltage drop, the current in the circuit will also change so one can use a voltmeter or ammeter to test the circuit. Realize that the change in temperature for the IC can come from external sources in much the same way as other temperature sensors are used, or the temperature change can come from a change in the amount of current flowing through the junction. An increase in current will cause an increase in temperature.
Above: Fig. 1 (a) Electrical diagram of an IC temperature
sensor used in a circuit with a variable resistor to provide a setpoint
setting. (b) Electrical diagram of two IC temperature sensors used with
an op amp.
