This project is to build a small Precision Constant Current Source Box which will give a 1mA and 10mA switched output which could be used to check the calibration of a digital multimeter. This project uses the LT3092 programmable two terminal constant current I.C.

Hey Louis.

Does this 100 ohms resistor have any influence on the calculatons in realation to current?

As I understand it, on the 1 mA range, you want 0,00099A from the output pin + 0,00001A from the set pin = 1mA.

That would give 0,198 volt on the set pin and the output pin aswell. The resistence on the set pin would be 19,8 K ohm. But I can get it to give any sense with this 100 ohm resistor in realation to calculation.

Regards Rasmus Haun.

Hey Louis.

Does this 100 ohms resistor have any influence on the calculatons in realation to current?

As I understand it, on the 1 mA range, you want 0,00099A from the output pin + 0,00001A from the set pin = 1mA.

That would give 0,198 volt on the set pin and the output pin aswell. The resistence on the set pin would be 19,8 K ohm. But I can’t get it to give any sense with this 100 ohm resistor in realation to calculation.

Regards Rasmus Haun

Hi Rasmus,

Since the 100 ohm is in series with the output current it has no effect on the output current set. This resistor is simply used to provide a reference voltage so you can simply calibrate the output current by monitoring the voltage across it when setting the 1K preset resistors during initial setup.

You are correct about your understanding how the 1mA output current is provided.

The 100 ohm resistor does NOT come in to the output current calculations. The output current does not change due the the 100 ohm.

Regards,

Louis

Hey Louis.

Tanks for your comment. I just took a on the datasheet. I says that the source current can be calculated as 10uA x Rset / Rout. If we then use your basic example in the start of your video, Then it would be 10uA x 20000 ohms / 200 ohms = 1mA. But I your case you got 1mA + 10 uA = 0.00101A

What is up and down in that case?

If I use my my example from before, then it would be 19800 ohms / 200 ohms x 10uA = 0.00099A

Regards Rasmus.

But if we then add 1% of the 1mA to the 0.00099A then we got 1mA.

Thanks Rasmus for your comments.

Regards,

Louis

Hi Louis, Excellent videos really enjoyable and informative.

I have brought all the parts for this project but I am unable to find a template or wiring diagram on this site. Would you by any chance have them available?

Thanks, Mark.

Louis Help… If you have the front fascia for the constant current source box could you please mail it to me and if there’s any wiring diagram?. Built the low current source today.

Excellent project thanks!

Regards

Mark.