MOSFET current source / current limiter request for review
The aim is to both keep component count and price low


Given your other limitations, it's hard to beat just a depletion mode MOSFET and a resistor. (I see where you are coming from, setting aside the JFETs.) I gather you are thinking of this:







simulate this circuit &ndash; Schematic created using CircuitLab

I can't tell from your writing just how repeatable you need to make this, though. The value of \$V_{GS\left(off\right)}\$ isn't all that precise. So you may need a potentiometer in there. Which ups the price, physical size, etc. Or you could just select parts, I suppose, and work it that way.

For example, the Supertex DN3525 specs \$V_{GS\left(off\right)}\$ anywhere from \$-1.5\:\textrm{V}\$ to \$-3.5\:\textrm{V}\$, with \$V_{DS} = 15\:\textrm{V}\$ and \$I_D = 1.0\:\textrm{mA}\$. Will that be repeatable enough without either selecting parts or selecting the resistor value?




  I am aware that a similar solution exists for JFET's, but I could not
  find a JFET type that can handle the voltage requirement.


You could use this topology to cover that concern:







simulate this circuit

However, with the devices shown you may need more headroom than just \$3\:\textrm{V}\$.



I know the load line approach would seem to get you there. But isn't the variability pretty significant? Or do you think it's good enough?