I'm trying to make (and try to learn something better) about a simple current regulator. I need to make a complete static analisys before starting with the frequency one. But I've some thoughts about how the base current will introduce errors and how a series resistor to the base will make it vary.
The circuit is this (available already made on the web, but with quite silly descriptions..). The values are not quite meaningful, because I'm still at literal calculations.
Here I've some troubles to extrapolate all the Kirchoff equations to analyze all the parameters (static ones) and so how Rb will influence the circuit.
For example, I find this:
Ib = Vbe/(Rb-Rs) - Rs*Id/(Rb-Rs)
where Id is the current flowing through the MOS M1.
But from here I recognize that Id = Vbe/Rs if we neglect the base current.
How can I give some meaning to the Ib equation, if it is correct? Should I fix the drain current then make the analisys? Of course, if I substitute the Id with Vbe/Rs, Ib will be 0, so the equation seems to be correct. But how to consider Id with the base contribution? Any help from where to start?