Need Schematic for Constant Current DC Supply

[0x00x0]

Hi,

I want to build a very simple circuit to allow me to input DC voltage from two to three 9 volt batteries, and get a constant current output of 0.5 mA.

Do you know of a handy schematic I can reference?

Thanks in advance.

 

[Willbe]

input DC voltage from two to three 9 volt batteries, and get a constant current output of 0.5 mA.

Doesn't get much simpler than this two terminal current source/sink \/

"A JFET can be made to act as a current source by tying its gate to its source. The current then flowing is the IDSS of the FET. These can be purchased with this connection already made and in this case the devices are called current regulator diodes or constant current diodes or current limiting diodes (CLD)."

 

[0x00x0]

Hi,

I looked into current limiting diodes, the lowest current value I could find was 22mA, I need it to be 0.5mA..

If you know of a 0.5 mA one I would love to hear of it, as it would be the simplest way...

 

[Willbe]

I looked into current limiting diodes, the lowest current value I could find was 22mA, I need it to be 0.5mA.

If you can find a 22.00 mA and 22.50 mA source you could wire them to subtract.

Never built one of these \/
https://en.wikipedia.org/wiki/Widlar_current_source
but you might work through the equations to see if it will work for your application. I know some manufacturers make matched transistors in one package.

Op amps are another way, but more complex.

 

[0x00x0]

I found one! **broken link removed**

It looks like this is just what I need.. But I do not understand the term "peak voltage" in the datasheet linked to above.

Here in the catalog it says:

Peak
Operating
Voltage (Min)(V)
40

So is that the minimum voltage or the max, or what?
see the catalog for more info:
https://www.mouser.com/catalog/635/498.pdf

Thanks again ..

 

[Willbe]

Good job!

the term "peak voltage" in the datasheet linked to above.

Check out footnote b and footnote e.
You have to stay between these limits [to prevent burnout?] and get the performance it was designed to provide.

 

[0x00x0]

Awesome, it looks like this will do just what I want, and it is only a buck! Thanks again!

 

[Willbe]

Awesome, it looks like this will do just what I want, and it is only a buck! Thanks again!

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[Roff]

Can you tolerate the fact that the tolerance is ±20 percent?