Switching properties of a partially set square-loop ferrite core

The switching properties of a partially set square-loop ferrite core depend not only upon the initial flux level, but also upon how that flux level was attained, and are therefore complex. Experimental results that describe some of this history dependence are presented. A thin-ring core (
OD/ID = 1.10
) was partially set by switching it from negative remanence (
-\phi_{r}
) to some flux level (φ
ps
) using a rectangular PARTIAL SET pulse of duration T
ps
. This pulse was followed by a rectangular TEST pulse having a variable amplitude
F
to determine the properties of switching from each partially set state. Three types of data were taken during the TEST pulse: 1) switching voltage waveforms [i.e.,
\phi(t)
] for a given φ
ps
and
F
, with T
ps
as a parameter, 2) peak switching voltage vs.
F
[i.e.,
\phi_{p}(F)
] curves for a given φ
ps
, with T
ps
, as a parameter, and 3)
\dot{\phi}_{p}(F)
curves for a given T
ps
, with φ
ps
as a parameter. The
\dot{\phi}(t)
waveforms changed considerably as T
ps
was varied, even though
F
and φ
ps
were constant (e.g., peaking time was reduced from 0.5 μs to less than 0.1 μs as T
ps
was reduced from 100 μs to 5 ns). The slope and threshold of the
\dot{\phi}_{p}(F)
curves were lowered considerably as φ
ps
was increased from
-\phi_{r}
to
-0.36\phi_{r}
(e.g., the slope was reduced by 40 percent and the threshold was reduced by 14 percent for
T_{ps} = 0.9 \mu
s). Presently used switching models are not able to account for these effects. Related phenomena also occur when the core is switched from
-\phi_{r}
with an MMF which is not constant throughout the entire switching process. The experimental results are discussed relative to the future development of an appropriate switching model.