Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Constant current source for sensor (LM317)

Status
Not open for further replies.
J

JoKKeR

Full Member level 2
Full Member level 2
Joined
Feb 14, 2008
Messages
130
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,298
Location
Estonia
Activity points
2,281
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 .
 

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
16_1265738802.jpg
 

    J

    JoKKeR

    Points: 2
    Helpful Answer Positive Rating
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.
 

    J

    JoKKeR

    Points: 2
    Helpful Answer Positive Rating
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.

-------

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

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top