I want to design a current source that can provide 2 different currents, 100mA and 1A using just a single power amplifier APEX MP38 which has a current limiting feature which is set by a resistor according to the following formula:
The maximum load that current should drive is an almost-pure resistive load around 50 Ohms.
I will supply the opamp +Vs by 60V and -Vs will be connected to GND.
Almost all opamp based current sources that I see, except Howland Current Pump which is too complex for my case (because I only need positive currents) use a PFET at the output of the opamp. Since the opamp that I have is already been purchased I kind of have to use it for this case.
Lets say I choose R3 and R4 in such a way that in parallel they make a sense resistor to limit the current to 1A, and when only R3 is conducting the current will be limited to 100mA.
So the questions are:
- Overall, do you think this is going to work?
- Is using a switch (e.g. cold-switching a relay) to switch between 2 different sense resistors a wise idea? is it a misuse of the current limiting feature which I beleive is only should be used to define a SOA?
- Having the -Vs connected to ground is OK or I need to provide the negative rail of the opamp with some voltage to get out of common mode voltage range?
- I want to use a 0-3V3 digital signal to turn on/off the output of the opamp. What sort of gain will I need? Do I need to use another opamp in buffer mode at an earlier stage before the main opamp?
- Do I need any capacitors in feedback or other paths (Of course the supply bypass caps are going to be there!)
UPDATE The load that I am talking about is a series of PCB traces that I want to see how do they perform under high-current stress. So it should be theoretically a resistive load with some small/negligible parasitic inductance/capacitance.