A circuit for reducing the exciting current of inductive devices

A negative feedback device is described in which the greater part of the exciting current necessary to energize a magnetic core is supplied by an amplifier, so that windings on the core present a much higher impedance than with the core material alone. An improvement of more than 100 times has been achieved at 50c/s. To the external circuit, the device appears as a composite core which may be wound in any desired manner. An investigation is made of the effect of using such a core on the voltage and current ratios of a 2-winding transformer, and a proposal is made for using a shielding technique to achieve high precision.