I would like to build a high side current source that can source 0-5A with a 1mA resolution. The voltage source feeding into this current source is a variable 0-50V that is always ~3V above the required voltage for that current.
My initial thought on doing this was to use a current sense amplifier as the inverting input to an op amp (the non-inverting input is the reference voltage) that controls a p channel MOSFET which controls the current going into the load. Unfortunately, this means that the current sense amplifier is inside the feedback loop of the op amp, which seems to be a problem (I'm getting lots of oscillations).
However, This note from analog shows a low side current sink using a difference amplifier to measure the current through a current sense resistor. It is using (a small amount of) positive feedback, which I don't understand.
This note from linear shows a low voltage, lower current (2A vs the 5A I want), current source. I'm worried about the integrator causing the transient response of the current source to be too slow, and thus too inaccurate.
This note from TI talks about separating the unity gain bandwidths of two amplifiers by a "factor of 5" when using an amplifier inside a feedback loop of another amplifier. (They mention this as a rule of thumb, but don't talk much about how to make it more concrete). However this seems really hand wavy, and it doesn't go into more detail.
What is the positive feedback for in the analog note?
Does this change the unity gain bandwidth of the op amp so the factor of 5 is obeyed? And does the amplifier INSIDE the feedback loop have to have a unity gain bandwidth greater than the one being fed-back?
What are other topologies for accurate current sources that can handle 5A?
: For example, if I have a 1A current into 10Ω, the adjustable power supply will be at 13V, and 2A current into 10Ω will give me a power supply of 23V, etc. The transient response of this response is a problem for another day...