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[FAQ] Remote Temperature Sensors — What remote BJT/Thermal diode should I use?

Remote Temperature Sensors — What remote BJT/Thermal diode should I use?

  • There are certain criteria that should be met when choosing a transistor to use for remote temperature sensing.

    1. Base-emitter voltage (VBE) is > 0.25 V at 6 μA, at the highest-sensed temperature.

    2. Base-emitter voltage is < 0.95 V at 120 μA, at the lowest-sensed temperature.

    3. Base resistance is < 100 Ω.

    4. Tight control of VBE characteristics indicated by small variations in hFE (that is, 50 to 150)

    5. Small transistor variation

    6. Consistent η-factor across temperatures

    Based on this criteria, the industry standard 3904 (NPN) or 3906 (PNP) are good choices for a remote temperature sensor.  However, any transistor should be evaluated for η-factor and consistency.