Bob Blick has a circuit on an SX forum, I happened across it the other day.

7 resistors and one op-amp (rail to rail) high side sensing.

V+in -    sense_R ---------- V+out

R_div_1a           R_div_2a   =20
R_div_1b           R_div_2b

0v-------------------------------

Op-amp V+ connects to R_div_1 centre tap
Op-amp V- connects to R_div_2 centre tap=20

Op-amp feedback resistor from op_v_out to op_V-
Resistor from op_V+ to 0v

Nominal values:
R1a,R2a 1M
R1b,R2b 100K (input voltage dived by 11)
Feedback R and R to 0v  10M
Sense resistor 5v/current to be sensed.

I notice that TI and Linear use either FET's or BJT's in the feedback loop,=
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byt they have converted from V to I and back to V.

Colin
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cdb, colin@btech-online.co.uk on 30/05/2011
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