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I am developing a redesign of a current PCB which uses the attached circuit in order to evaluate the temperature using a PTC thermistor (which is R3 in the given image). The circuit is connected to three ADC/GPIO pins of a microcontroller.

I have looked through a few application notes, but I haven't found this type of PTC evaluation circuit. Can anyone tell me how this circuit would work and what the advantage of this circuit would be? What alternative PTC circuits would you recommend for a temperature sensing application? I would like to keep the PTC as the sensing element, however I am unsure how I would get a temperture-compensated, high-accuracy PTC circuit.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Somehow this doesnt look correct. There is no DC path for PTC (1K). Also, could you tell me what is the difference between sense and temp? seems similar meaning. Also why 3 pins? I feel voltage across PTC is more than sufficient to sense the temperature difference. I am visualising a circuit more like this : m.eet.com/media/1074719/0202feat1fig2.gif \$\endgroup\$
    – rsg1710
    Commented Nov 8, 2017 at 10:27
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    \$\begingroup\$ The problem with the circuit as you've drawn it is that whatever is connected to TEMP, SENSE, REF and VDD pins makes or breaks the functionality of the circuit. Only if SENSE would be pulled low (or high) and REF would be connected to a reference voltage then at TEMP we could measure a temperature dependent voltage. Having a SENSE line like that has the advantage that (most of the) current only flows when SENSE is low and a measurement is being done (which saves power). \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 8, 2017 at 10:28
  • \$\begingroup\$ I tend to think that the intention was to be able to disconnect the PTC circuit (by pulling the pins to GND/HIGH appropriately) and therefore to keep self-heating at a minimum. Would you agree? However, would it not be more practical to use a transistor-based current source in order to drive the thermistor? What circuit would you prefer over the described one? \$\endgroup\$
    – Havefun
    Commented Nov 8, 2017 at 11:38

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