Current monitor uses Hall sensor

Paul Galluzzi, Dynamics Research Corp, Wilmington, MA; Edited by Paul Rako and Fran Granville - January 5, 2012

Originally published in the March 31, 1987, issue of EDN

The Fig 1 circuit uses a Hall-effect sensor, consisting of an IC that resides in a small gap in a flux-collector toroid, to measure dc current in the range of 0 to 40A. You wrap the current-carrying wire through the toroid; the Hall voltage V_H is then linearly proportional to the current (I). The current drain from V_B is less than 30 mA.

Current monitor uses Hall sensor figure 1

To monitor an automobile alternator’s output current, for example, connect the car’s battery between the circuit’s V_B terminal and ground, and wrap one turn of wire through the toroid. (Or, you could wrap 10 turns—if they’d fit—to measure 1A full scale.) When I=0V, the current sensor’s (CS₁’s) V_H output equals one-half of its 10V bias voltage. Because regulators IC₁ and IC₂ provide a bipolar bias voltage, V_H and V_OUT are zero when I is zero; you can then adjust the output gain and offset to scale V_OUT at 1V per 10A.