Help with LM334Z

[silverviper]

Hi

I'm having some difficulty tuning this circuit.

http://www.datasheetcatalog.org/datasheet/stmicroelectronics/2157.pdf

My power source is 23.9VDC 300mA.
I need the current output be limited @ 0,9 mA.

I've set my resistors as following.

R1 = 0,134V / 0,009A ~ 150 ohm
R2 = R1 * 10 = 1,5kohm

I will use this circuit to limit the current between two .9999 pure silver electrodes
in a container/jahr with distilled water. (making Colloidal Silver)

When I start it up the conductivity in the water is low and i'm reading 0,35mA and 22,8 Volts over the electrodes.
As silver ions are released from the anode (positive electrode) in to the water, the conductivity goes up, as does the amp.


The circuit does not limit the current to 0,9mA, after an hour or so i'm reading 3.35mA and 21,5V over the electrodes.

I'm going nuts over this "simple" circuit, so any help is much apprechiated.

Thx


Chris

 

[MikeMl]

Read the **broken link removed**, starting on page 6. It has a much better explanation of how to ratio the two resistors.

 

[silverviper]

thx Mike,

Has anyone built this circuit?

 

[ericgibbs]

thx Mike,

Has anyone built this circuit?

hi SV,
Whats the constant current with the two probes shorted together,,, out of the liquid.???

It should be 0.9mA.

 

[silverviper]

thx

my current reading is 139,6 - 140,2 mA during a sustained short.

Chris

 

[ericgibbs]

thx

my current reading is 139,6 - 140,2 mA during a sustained short.

Chris

hi,
As you have already guessed the constant current circuit is not working as it should.

Are you using a 1N457 diode, also check that you have used/read the correct resistor values.

I assume that you have the constant current circuit is series with one of the tank leads.??

 

[silverviper]

hi

I'm using a 1N4148 signal diode, and i'm reading 0,8V over it.

+ 23,9V -------[Lm334Z]-------------[Anode]>

------------------------------------[Cathod]>

Resistors show correct values, and i've tested with two other LM334Z's

Chris

 

[ericgibbs]

hi,
Ive downloaded the LTspice LM334/335 models, I will try to simulate your circuit, let you know.

 

[ericgibbs]

hi Chris,
This what I get from the LTS simulation for the LM334.

I have stepped the probe path from 1000R to 1R and the current is close to 0.9mA for these loads.
Can you post a sketch showing how you have the components connected.?

 

[silverviper]

thx

Chris

 

[ericgibbs]

thx


Chris

hi Chris,
Is it now working OK.?

 

[silverviper]

Thanks again

no its not working. My circuit is as the schematic shows,
i've traced every lead to make sure its corretly assembled.

 

[atferrari]

Have checked the voltage?

I have checked the maximum oltage myself and it seems that you are on the safe side.

Realized that I forgot how to calculate the whole thing.

 

[silverviper]

Thanks

I'll assemble a new circuit. Please check
this thread tomorrow.

Chris

 

[atferrari]

hi Chris,
This what I get from the LTS simulation for the LM334.

I have stepped the probe path from 1000R to 1R and the current is close to 0.9mA for these loads.
Can you post a sketch showing how you have the components connected.?

View attachment 38218

Not to bring this thread off track, Eric, but how did you manage to test R from 1 to 1000?

Not obvious to me, at least.

 

[ericgibbs]

Not to bring this thread off track, Eric, but how did you manage to test R from 1 to 1000?

Not obvious to me, at least.

hi,
I defined Rx the 'load' as a {Rx} variable in LTS and then the LTS directive .step param Rx 1000 1 100.

This runs the runs a plot of Rx from 1000R to 1R in 100R steps.

OK.?

 

[ericgibbs]

Thanks again

no its not working. My circuit is as the schematic shows,
i've traced every lead to make sure its corretly assembled.

hi Chris,
The only conclusion is that either the LM344 is 'the wrong way around' in your project or they are 'blown'.

By wrong way around , you may have read the LM344 pins 1,2,3 in reverse.

As the LM344 is quoted a 40Vmax working voltage, I don't believe that the 28Vdc is the problem.

 

[silverviper]

Hi

I built a new circuit as you suggested, the current still rises to well above
3mA.

I don't think the LM334's are blown, i've got a dosen of brand new ones,
i'ts odd that all are blown, i'll try to reverse the pinout when i get home from work.

Thanks again for your assistance.


Chris

 

[ericgibbs]

Hi

I built a new circuit as you suggested, the current still rises to well above
3mA.

I don't think the LM334's are blown, i've got a dosen of brand new ones,
i'ts odd that all are blown, i'll try to reverse the pinout when i get home from work.

Thanks again for your assistance.


Chris

Chris,
For ref I have run the sim for temperatures from 5C thru 35C, looks OK.

 

[silverviper]

Hi again

After a closer look on the spec, it seems i got it wrong the first build.
I just tried with the reversed/correct pinout on a fresh LM334, but its still not working.


A dead short between the probes, shows 60mA on my DMM, the last build showed a 140mA

I've installed this LTSpice and replicated my circuit there,
and my simulation is nearly identical to yours.

Chris