Dc Current And Inductor Saturation - Stanford Research Systems SIM954 Operation And Service Manual

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3.3.1 DC Current and Inductor Saturation

TDS 3034 29 Jul 2008 10:38:24
Figure 3.5: Voltage on fluxgate magnetome-
ter coil driven with 10 kHz sine wave
Since inductors are essentially DC shorts, driving even a small DC
voltage on an inductor will lead to large DC currents. It is important
to verify that the amplifier's current and thermal power dissipation
limits are not violated by such a condition, and that the inductor
is actually able to handle the output current. Core saturation in
inductors wound on iron or ferrite cores should be avoided because
of the rapid rise in losses for AC currents in the saturated core.
Figures 3.5 and 3.6 show an example of inductor saturation. The
SIM954 is driving an ultra-high permeability core with almost rect-
angular magnetization curve, used in a fluxgate magnetometer, with
a 10 kHz sine wave. The core saturates shortly after the voltage on
the coil passes the extremal values. Because of the rapid loss of the
core's ability to store any further magnetic energy, the voltage on
the coil breaks down, while at the same time the current increases
rapidly.
Since the voltage at the output of the module goes to zero at the
same time the output current rises, a saturated inductor presents
a very heavy load to the amplifier. In general it is better to avoid
saturating inductors. However, if the SIM954 is used to deliberately
drive inductors into saturation, as in the example of the flux gate
magnetometer coil, care should be taken to avoid the amplifier's
current and thermal limits.
SIM954 300 MHz Dual Inverting Driver Amplifier
TDS 3034 29 Jul 2008 10:54:59
Figure 3.6: Current through fluxgate mag-
netometer driven with 10 kHz sine wave
Application notes