APPLICATION NOTE
5
EOUT Z1 10 VALUE={V(GEOM)*V(BIAS)*V(ZREF)}
VSENSE 10 Z2 DC 0
GCOPY 0 ZREF VALUE={I(VSENSE)}
* * Impedance correction for bead size and number of turns * *
EGEOM GEOM 0
+ VALUE={N*N*(0.417+3.41*L*LOG10(OD/ID_Bead)) }
RGEOM GEOM 0 1MEG
* * Impedance correction for DC current bias, turns and diameter * *
EBIAS BIAS 0 TABLE {I(VSENSE) * N / (OD/0.2)} =
+ (-14,0.09)(-10.0,0.14)(-8.0,0.17)(-6.0,0.23)(-4.0,0.37)
+ (-2.0,0.77) (-1.0, 0.9) (0.0,1.0) (1.0,0.9) (2.0,0.77)
+ (4.0,0.37) (6.0,0.23) (8.0,0.17) (10.0,0.14) (14,0.09)
LBEAD ZREF 0 3U
RBEAD ZREF 0 111
CBEAD ZREF 0 {1.4P*N}
.ENDS
The bead is modeled in PSpice by using a basic impedance multiplier. The Circuit Design is shown in the Figure
below. The circuit operates by sensing the AC current flowing through the bead and producing the voltage that
relates to the correct impedance for that AC current and frequency.
The equation for this is Vout = Z x Iin
Figure 5: Circuit Design for bead_73
To make this equation applicable to all circuit configurations of a bead, EOUT takes inputs from the geometry of
the bead, DC bias level, number of turns, and the reference bead impedance to produce the correct equivalent
impedance.
