Temperature compensated high efficiency inductor current sensor

Inductor current sensing is very important in the control and monitoring of switching power converters. Traditional low cost implementation using a sensing resistor in series with the inductor will reduce the overall efficiency of the power converter. Conventional Hall effect current sensor could also be used to detect the inductor current. However, it will significantly increase the production cost of power converters. One simple and low cost implementation is to add a resistor-capacitor (RC) network in parallel with the inductor so that the inductor current can be derived from the added circuitry. The problem with RC sensing network is that the sensed variable is very sensitive to temperature variations. In this paper, a novel inductor current sensor using low cost negative temperature coefficient (NTC) thermistors to compensate the variation in the parasitic resistance of the inductor due to temperature changes is proposed. The changes in the cutoff frequency and steady state gain are also compensated by the added NTC thermistor circuit. With the compensated network, the sensed inductor current derived from the modified RC network will be independent of temperature variations. The compensated network can be applied to inductors fitted to power converters. Although experimental studies based on a buck converter were carried out to illustrate the correctness of the improved sensing technique, the proposed technique is applicable to other converter topologies. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.