Constant current source for sensor (LM317)

[JoKKeR]

Hi !


How can i design constant current source (1mA) for a resistance based temperature sensor. Sensor resistance is 2Komh. (LM317)

Because i do not understand this topic fully im not sure about correct description of my problem, I hope you can help me out.

Basically... I need to to integrate a thermistor to a PIC MCU. 1mA cont source current seems good because i can get 2 V as voltage drop, out of 2Kohm resistor in series .

 

[garg29]

This source provides a constant current supply to a circuit load. Note that the transistor current source is inside the feedback loop. Here, R1 and R3 make a voltage divider to set Vref, but Vref could be set by some other voltage signal, instead. The current is determined by the formula:

Current Out = (V+ - Vref) / R2

 

[Audioguru]

An LM317 has an operating current as high as 10mA so its minimum regulated current is more than 10mA. Most have an operating current of 3.5mA.

 

[JoKKeR]

Thank you !

Id appropriate a hint to solution of my problem:
How to measure correct resistance from 2Kohm thermistor as voltage on PIC ADC channel.

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I v got NOT LM317 but a LMx34 (adjustable current source) :S