The current source iRF3205 in the picture is not turned on, please help you guys, how to modify the circuit without modifying vcc to make the current source work normally (its load resistance range is 0-10 ohms). My idea is to add a voltage amplifier circuit to the u2a power supply voltage, but I just learned these without hands-on experience, I do not know whether the operation is feasible in reality?
Jameson Posted on July 15, 2020
If the power supply voltage is 7V, the current source can work normally, and when it is 5V, it cannot work normally, indicating that the driving voltage provided by the LM358 fails to drive the IRF3205. The threshold voltage of IRF3205 is 2V minimum and 4V maximum, and 358 is not a rail-to-rail op amp, so it is normal that its high level does not reach the threshold voltage of IRF3205. You can use MOS tube with lower Vgs(th).
Jakob Posted on July 15, 2020
Q1 is replaced with a triode.
Dallas Posted on July 15, 2020
Modify the VRF voltage of iRF3205 from 20 to 2..
