lm334 constant current generator

[bmandl]

Hello everyone,
I designed constant current generator with LM334 IC but it doesn't work as I expected. I need a current that must not exceed 0.95mA. My load is getting smaller with time and current is increasing, but must not exceed 0.95mA. I am using circuit from page 8 in this datasheet and I calculated resistors as 150Ω for R1 and 1.5kΩ for R2 in E24 scale. That should give about 0.92mA of current if I am correct. I use 1n4148 for diode. My voltage source is 24V DC.
The problem is, that when conductivity of a load is increasing, current exceeds my limit and goes up above 1.2mA and more. This is too much tolerance for my application. And even then if I reduce voltage, current is changing back down, but it should be constant at 0.92mA. Did I missed something in my design?



PS.: My application is colloidal silver generator. In the begining, the load is distilled water but with time its conductivity is increasing because of electrolysis. The current must be constant through the process.

 

[crutschow]

What's the purpose of the diode?
The circuit in the data sheet that uses a diode for temperature compensation, also uses two resistors.

 

[D.A.(Tony)Stewart]

Normally Colloidal silver is generated with high V transformer and variac and big 50W power large value R to limit current.

 

[red_alert]

You have to switch V- and R (ADJ) pins.

 

[bmandl]

You have to switch V- and R (ADJ) pins.

Sure, I made a mistake. Now, I have to make whole pcb again:evil:
Thank you.

- - - Updated - - -

Ok, I corrected the PCB and now I get 905uA at 24V. It is still quite a difference, but at least now it is responding as current source. And besides, smaller current is better for colloidal silver. It is perfect now. Thank you again red_alert, for noticing my error.