4mA current regulator

[panfilero]

can anyone offer any suggestions on how to make a simple 4mA current regulator... I started looking at LM317 voltage regulators, but found that they're gonna output a minimum of 10mA... I'm now looking at JFETs with a resistor between the source and gate... most the JFETs I'm finding can only provide currents less than 3mA...

thanks

 

[Reloadron]

Go and read this thread and note the posted circuits with a focus on what Eric posted. That should get you going as to a 4 mA current source.

Ron

 

[edeca]

Just out of interest, what do you need one for?

 

[panfilero]

On Jun 24, 12:57*pm, panfilero <panfil...@gmail.com> wrote:
Thanks for the responses... what I'm trying to do is power an
accelerometer.... *I'm trying to re-create the "Constant Current
Signal Conditioner" side of the circuit shown in Fig. 7 of this link

**broken link removed**

but in that circuit they use a "Current Regulating Diode" I don't have
one of these, but I do have an electronics store down the street, so
basically that's what I'm trying to re-create, and for the
accelerometer I have, the current would have to be regulated to 4mA...
thanks

 

[MikeMl]

So you are trying to supply ~4ma to the open drain of the built-in FET, where the drain voltage is near 10V.

What is your supply voltage? They show about 20V.

 

[panfilero]

yes, I'm trying to supply 4mA to the top leg of the fet (I'm not very clear on how these things work or why). I called the people who make this accelerometer and they said 4mA constant current, and the VDC power at about 24V would be good... one thing I don't understand about this circuit is... if they have 18-30V in series with a diode on one leg, and there's another parallel leg with a Volt-meter on it, how is that meter reading 10V ? I thought the idea in parallel things was that the voltage across two parallel legs would be the same...

thanks

 

[RCinFLA]

Current mirror - Wikipedia, the free encyclopedia

 

[MikeMl]

Current mirror - Wikipedia, the free encyclopedia

Using RC's suggestion:

You will likely need additional amplification, and some filtering. Note that a variation of 10uA produces about 0.5V out.