IC (Integrated circuit) temperature transducers


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The Integrated circuit temperature sensor is commonly known as a local temperature sensor, that measures its own die temperature using the physical properties of bipolar transistors. Some local temperature sensors have analog outputs (either voltage or current), while others include an internal ADC and produce a digital output in one of several formats.

Temperature measuring sensor ICs have tremendous flexibility in implementation.

Working:

The IC temperature (ICT) transducer is a two-terminal monolithic integrated circuit whose output is a current or a voltage that is directly proportional to temperature T/K. The transduction mechanism utilized in this transducer is the dependence of the base-emitter voltage Vbe of a silicon transistor, on the ambient temperature T/K.

If two well-matched IC transistors are connected as shown in above figure, then the difference between the Vbe’s of the transistors Q1 and Q2 is proportional to T, if the ratio of the respective emitter areas O is constant. It is made constant by designing the emitter areas of Q1 and Q2 to be in a fixed ratio and operating them at equal collector currents.

When the temperature being monitored changes, the collector currents of Q1 and Q2 also change. The control circuit as drawn in Figure above forces the collector currents to equalize, and V0 is then proportional to the temperature being measured. The total output current IOUT through Q1 and Q2 is

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I out is then proportional to T/K if R0 is constant. In practice, R0 has a very small temperature coefficient of resistance. The transducer is connected in series with R1 and R2 to produce a voltage drop proportional to T/K. The ICT transducer operates in the range -55 to +150°C with very good linearity.

Uses of IC temperature transducers:

  • Use to sense the temperature of a printed circuit board (PCB) or the ambient air around it.

  • Use to measure the temperature of PCs to temperature control systems, High-performance personal computers and servers use monolithic temperature sensors on their motherboards to monitor system temperatures and alert system failure.

  • Simple Fan Controller: senses the temperature and control the fan speed