At first, a review of known magnetic-coupled current-sensing techniques is
presented. Subsequently, a novel technique is introduced, based on a config
uration discussed in a previous paper. The previous technique made use of a
galvanomagnetic device (Hall-effect sensor) to sense the magnetization of
a current transformer core, so that the sum of the Hall voltage and the vol
tage across the secondary shunt resistor would yield a faithful copy of the
input current. The technique described in this paper makes use of the same
principle to obtain a high bandwidth (from de to 1 MHz) and very high comm
on-mode rejection current transformer, without the need for a Hall-effect p
robe. This is achieved by subtracting the high-frequency components, detect
ed across the secondary shunt resistor, from the voltage across a primary s
hunt resistor connected in series with the primary of the current transform
er. The resulting signal is an accurate image of the transformer magnetizin
g current, which is then transferred to the secondary side by means of a lo
w-bandwidth isolation amplifier. The high-frequency components are subseque
ntly added, to the amplified and filtered low-frequency components, by mean
s of a third transformer winding, the number of turns of which is chosen to
be equal to the gain of the low-frequency amplifier.