Hi all,
I am currently studying this constant current source with opamp and P channel MOSFET. there is something I do not understand and that I would like to ask. The way I see it, the opamp will alwas drive the gate of the MOSFET so as to keep the negative input to the same voltage as the positive input. I would therefore expect that if I increase the reference voltage to 5V, the gate voltage will rise high enough to completely turn OFF the mosfet and to ensure the negative input also reaches 5V. I do not see this behaviour in simulation, though. If I rise the VREF voltage, the VGAT only increase so much, and the Vin voltage is clamped somewhere at 4.15V. So I guess the question is: why doesn't the opamp block the MOSFET when VREF=5V?