Can I use the same resistors for current shunt AND transistor balancing? Answered
In my pursuit for a LPSU design, to get more HFe gain, higher current capability, decrease Vce dropout, improve thermals, etc. I would use 2 (or more) pass transistors. This requires load balancing resistors, so I thought I'd get clever and use these balancing resistors to also measure current for my current limiting capability! See pictures and explanation below.
IMPORTANT: The second schematic implys the use of 100R resistors, that is a mistake, they are supposed to be 0.1 ohm, or around that figure.
The first picture below is a simplified diagram of how I currently have current feedback implemented. I generate a fixed (user adjustable) voltage across a 500R resistor via a current sink and an error amp (currently LM358) drives output pass transistor(s). Because the op amp drives the output to ensure the inputs are the same, the output current can be precisely regulated. It maintains a precise voltage differential across the shunt by means of the pass transistor.
I don't want to take the naive approach with multiple resistances in the path of the current flow from the unregulated supply to the output, for obvious reasons. I could instead just measure the Vdrop on one of these balancing resistors, but that assumes that the current through those resistors is identical, which is not the case. So instead, what if I expand a bit on the first schematic, leading to the last schematic? Would that work? I want to understand the mathematical analysis behind it to prove it does work.