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This paper investigates the static and dynamic performance of current sense methods, which exploit the resistive voltage drop across the current carrying copper trace. This approach promises very low cost since no dedicated shunt resistor is required, no additional power losses occur and no extra space on the printed-circuit-board (PCB) is necessary. A microcontroller can be used to calibrate the copper trace resistance and implement a temperature drift compensation by means of a temperature sensor. Given that today almost every electronic device has at least one microcontroller that can provide the small computation power required for this current sensing technique, the additional cost of such a technique is small.While the proposed technique appears straightforward, theoretical modeling and hardware experiments revealed two unexpected obstacles. First, the thermal resistance between the busbar and the temperature sensor notably alters correction for the temperature drift. We found that it is possible to rectify this behavior by implementing a more sophisticated temperature compensation method inside the microcontroller. Second, it is demonstrated that the self-inductance of the busbar arrangement is not important for the dynamic behavior (frequency response) of this measurement method, and the response is determined by the mutual inductance between main loop and sense loop. Based on simulation and measurements, we demonstrated that a simple RC-compensation network can significantly improve the frequency response.
Date of Publication: July 2009