Programmable Constant Current Source

[mrpicing]

I need a 10-Bit programmable constant current source 0~1mA range(Single or Multiple Output).
I want to interface it with PIC16F877A. But i faild to find any current source completing my requirment . Can any body tell me any part number
or any hint about it? Thnaks.

[jma_1]

Greetings,

A 10 bit 0-1 mA current source is an interesting animal. Why only 0 - 1 mA? I cannot think of anything which would require the resolution you are talking about (1 uA). You might be better off purchasing a programmable power supply with the necessary resolution and controlling it with a PIC.

How are you going to measure the current to verify the accuracy? Does the application need a linear response?


A link to an example of a programmable current source (0-20 mA) is listed below. The programmable 'feature' is using a digital potentiometer.

http://www.elecdesign.com/Articles/ArticleID/10115/10115.html

Another implementation using a digital pot

http://www.maxim-ic.com/appnotes.cfm/an_pk/3464

You might try playing with a 'Howland' constant current source. This is simple enough to build, but your requirement of 0-1mA makes the circuit very interesting.

[asmallri]

[jma_1]

Thank you asmallri. I have not had the pleasure of using an RTD sensor in a design yet.

Cheers,
JMA

P.S. Is it almost time for the 'Royal Show' in Perth? :-)

[Charlie U]

Do a google search for the "Howland Circuit". It is a simple voltage to current converter. There are several variants available, so just pick one that you like and experiment a bit with it. Once you have the current converter working, you could drive it from the micro with either a filtered PWM output or a DAC.

[mrpicing]

aoa.
Thanks every body for ur kind responce . Basiclly i need a 8-channel programmable current source. Its resulotion may be greater than 10bits.
Its range is 0 to 1mA or nearest.

I need it to simulate 8 temperature sensors (each 1uA/Kalvin). I need very precise current source. i want to avoid to build complex circuit .

now i'll try ur suggessions & links. Thanks.
Hav a nice day.

[Kenny]

Sounds like you are using a temperature sensor like the AD592. The output current depends on the temperature, but is independent of the supply voltage (as long as there is enough 'overhead').

At some stage you must be converting the current to a voltage with a resistor, so your project then would be to simulate this voltage. For example use the pic to set a dac output to a precise resistive divider, then a low output-offset buffer op. amp.

The slope of 1uA/deg K is very accurate on the AD592, but the initial error without trimming can be a couple of degrees.

[mrpicing]

aoa. Yes u r right. a resistor is being used as current to voltage converter but if resistor get faulty then the system will work ok. and i can't under stand that any thing is wrong. that's why i decided to use current source to avoid this.
Thanks