Low cost inductor current sensing for power converters using feedback compensation

One of the key components in the Current mode control of power converters is the sensing of inductor current. Traditional low cost implementation is to add a sensing resistor in series with the inductor to sense the inductor current. This will reduce the overall efficiency of the power converter. An alternative is to apply a current transformer to the inductor to sense its current. This however will significantly increase the cost of power converters. One low cost implementation is to add a resistor-capacitor network in parallel with the inductor so that the inductor current can be derived from the capacitor voltage. The problem of this implementation is that the capacitor voltage is very sensitive to temperature variations. In this paper, a simple feedback loop is applied to the sensed capacitor voltage based on the steady state duty ratio of power converters such that the sensed inductor current will be independent of temperature variations. The sensing element with feedback compensation can be applied to inductors fitted to power converters Such as buck converters and boost converters. Although experimental studies based on a buck converter were carried Out to illustrate the correctness of the new sensing technique, the proposed technique is applicable to other converter topologies. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.