I've been looking at various ways to measure current for a while now, and am stumped on how to read high-side AC Current Measurements ohmically (no Hall Effect sensors). My initial thought was to use PNP and NPN BJTs in parallel (one of each), connecting them across a 0.1 Ohm current sense resistor (basically making a differential amplifier). I can't seem to make a circuit that works in this configuration, however, and differential amplifier ICs can't handle the high voltages I'm looking to measure (up to 600VAC). I've seen a op-amp from Analog Devices that can handle common mode voltages up to 600V, but am trying to make a circuit just from discrete circuit elements to start.
My question is mainly this: is it possible to measure high-side AC current with just a few BJTs and/or MOSFETs? My ideal circuit would do the following:
Vin=600VAC, 0.1Ohm current shunt resistor on the high side, Current=1 Amp AC. --so-- V1=600VAC V2=600VAC-(0.1 Ohm) * (1 A) = 599.9VAC
BJT circuit takes V1 and V2 as inputs, and gives 0.1VAC (V1-V2).
Thanks for all your help! The replies don't have to be an answer to the question, more trying to understand how something like this could be possible.