Hmmm - when configured in a constant current configuration I suppose you could say its a current source, but that's not the MOSFET, that's the circuit configuration. It isn't a current source in the sense that a battery is a current source.A MOSFET does act somewhat like a current source when it is in saturation mode. For any given gate voltage, there is a max current after which the current increases very little with increase in Vds.
Well, the added circuitry controlling the MOSFET does help in establishing and stabilizing the current-limit, but the MOSFET makes a pretty good current-source by itself if operated in the saturation region (below), as can be seen by the near constant current for a change in the drain-source voltage.when configured in a constant current configuration I suppose you could say its a current source, but that's not the MOSFET, that's the circuit configuration.
OK, that might have been a bad choice of example, it was a WIP on another project and I picked the first diagram with a single MOSFET as an example confi. For completeness here are the LTSpice generated curves for that device for Vgs = 4.15 - 4.85V:Is the load actually 0.75milli-ohms which is only 0.00075 of an ohm?
The Mosfet needs a Vgs of 10V to fully turn on and the minimum opamp output voltage will be 11.2V then the output current will be (11.2V - 10V)/0.00075= 1600A (!) and explode it and the battery if the input voltage is at the maximum input for the opamp of 12V - 1.5V= 10.5V.
If the load is actually 0.75 of an ohm then the output current will be 667mA.
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by Jake Hertz
by Jake Hertz