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Created March 19, 2012
Last modified March 19, 2012
Tags current-mirror   current-monitor   current-sense   high-side  


A precision high side current monitor.

Converts a current to ground into a ground referred positive voltage output.


A simple, low cost way to convert the current flowing into a grounded load into a ground referred positive voltage with excellent precision.

The voltage drop due to the Rmon can be made negligible by setting a suitable transconductance (Vout/I_load). The choice of a very low offset opamp such as an AD8551 allows this circuit to be used to monitor currents well below 1uA whilst using very low value resistors to accommodate higher currents.

The voltage output can then be fed into a buffer amplifier or ADC as required. Note that the input impedance of any such buffer or ADC will appear in parallel with Rout and so will affect the transconductance of the circuit.

Note also that the opamp must have an input specification that allows a common mode voltage of up to and including the positive rail.

At present, the opamp models available in CircuitLab are not accurate enough to show the detailed behaviour of the part number chosen so check your nominated opamp datasheet carefully before committing to a design.


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