Many electronic devices, such as voltage converters, motors, etc., include electromagnetic components through which the current flow must be estimated. Such electromagnetic components include transformer windings, motor windings, and other types of inductors. In order to estimate the current through such components with reasonable accuracy and without unnecessary power loss, the inherent resistance of the electromagnetic component is used in conjunction with an auxiliary winding through which effectively no current flows. A first terminal of the auxiliary winding directly connects to a first terminal of the electromagnetic component and runs in parallel to the component. The voltage across a second terminal of the auxiliary winding and a second terminal of the electromagnetic component is measured and closely approximates the voltage across the equivalent series resistance (ESR) of the electromagnetic component. This measured voltage is used to estimate the current through the component.