Ferrites and accessories
Cautions and warnings
Mechanical stress and mounting
Ferrite cores have to meet mechanical requirements during assembling and for a growing number
of applications. Since ferrites are ceramic materials one has to be aware of the special behavior
under mechanical load.
As valid for any ceramic material, ferrite cores are brittle and sensitive to any shock, fast changing
or tensile load. Especially high cooling rates under ultrasonic cleaning and high static or cyclic loads
can cause cracks or failure of the ferrite cores.
For detailed information see chapter
“Definitions”,
section 8.1.
Effects of core combination on A
L
value
Stresses in the core affect not only the mechanical but also the magnetic properties. It is apparent
that the initial permeability is dependent on the stress state of the core. The higher the stresses are
in the core, the lower is the value for the initial permeability. Thus the embedding medium should
have the greatest possible elasticity.
For detailed information see chapter
“Definitions”,
section 8.2.
Heating up
Ferrites can run hot during operation at higher flux densities and higher frequencies.
NiZn-materials
The magnetic properties of NiZn-materials can change irreversible in high magnetic fields.
Processing notes
– The start of the winding process should be soft. Else the flanges may be destroid.
– To strong winding forces may blast the flanges or squeeze the tube that the cores can no more
be mount.
– To long soldering time at high temperature (>300 °C) may effect coplanarity or pin arrangement.
– Not following the processing notes for soldering of the J-leg terminals may cause solderability
problems at the transformer because of pollution with Sn oxyd of the tin bath or burned insulation
of the wire. For detailed information see chapter
“Processing notes”,
section 8.2.
– The dimensions of the hole arrangement have fixed values and should be understood as
a recommendation for drilling the printed circuit board. For dimensioning the pins, the group
of holes can only be seen under certain conditions, as they fit into the given hole arrangement.
To avoid problems when mounting the transformer, the manufacturing tolerances for positioning
the customers’ drilling process must be considered by increasing the hole diameter.
3
07/14
Ferrites and accessories
Symbols and terms
Symbol
A
A
e
A
L
A
L1
A
min
A
N
A
R
B
ΔB
ˆ
B
ˆ
ΔB
B
DC
B
R
B
S
C
0
CDF
DF
d
E
a
f
f
cutoff
f
max
f
min
f
r
f
Cu
g
H
ˆ
H
H
DC
H
c
h
h/μ
i
2
I
I
DC
ˆ
I
J
k
k
3
k
3c
L
Meaning
Cross section of coil
Effective magnetic cross section
Inductance factor; A
L
= L/N
2
Minimum inductance at defined high saturation (
μ
a
)
Minimum core cross section
Winding cross section
Resistance factor; A
R
= R
Cu
/N
2
RMS value of magnetic flux density
Flux density deviation
Peak value of magnetic flux density
Peak value of flux density deviation
DC magnetic flux density
Remanent flux density
Saturation magnetization
Winding capacitance
Core distortion factor
Relative disaccommodation coefficient DF = d/μ
i
Disaccommodation coefficient
Activation energy
Frequency
Cut-off frequency
Upper frequency limit
Lower frequency limit
Resonance frequency
Copper filling factor
Air gap
RMS value of magnetic field strength
Peak value of magnetic field strength
DC field strength
Coercive field strength
Hysteresis coefficient of material
Relative hysteresis coefficient
RMS value of current
Direct current
Peak value of current
Polarization
Boltzmann constant
Third harmonic distortion
Circuit third harmonic distortion
Inductance
4
07/14
Unit
mm
2
mm
2
nH
nH
mm
2
mm
2
μΩ
= 10
–6
Ω
Vs/m
2
, mT
Vs/m
2
, mT
Vs/m
2
, mT
Vs/m
2
, mT
Vs/m
2
, mT
Vs/m
2
, mT
Vs/m
2
, mT
F = As/ V
mm
–4.5
J
s
–1
, Hz
s
–1
, Hz
s
–1
, Hz
s
–1
, Hz
s
–1
, Hz
mm
A/m
A/m
A/m
A/m
10
–6
cm/A
10
–6
cm/A
A
A
A
Vs/m
2
J/K
H = Vs/A
Ferrites and accessories
Symbols and terms
Symbol
ΔL/L
L
0
L
H
L
p
L
rev
L
s
l
e
l
N
N
P
Cu
P
trans
P
V
PF
Q
R
R
Cu
R
h
ΔR
h
R
i
R
p
R
s
R
th
R
V
s
T
ΔT
T
C
t
t
v
tan
δ
tan
δ
L
tan
δ
r
tan
δ
e
tan
δ
h
tan
δ/μ
i
U
Û
V
e
Z
Z
n
Meaning
Relative inductance change
Inductance of coil without core
Main inductance
Parallel inductance
Reversible inductance
Series inductance
Effective magnetic path length
Average length of turn
Number of turns
Copper (winding) losses
Transferrable power
Relative core losses
Performance factor
Quality factor (Q =
ωL/R
s
= 1/tan
δ
L
)
Resistance
Copper (winding) resistance (f = 0)
Hysteresis loss resistance of a core
R
h
change
Internal resistance
Parallel loss resistance of a core
Series loss resistance of a core
Thermal resistance
Effective loss resistance of a core
Total air gap
Temperature
Temperature difference
Curie temperature
Time
Pulse duty factor
Loss factor
Loss factor of coil
(Residual) loss factor at H
→
0
Relative loss factor
Hysteresis loss factor
Relative loss factor of material at H
→
0
RMS value of voltage
Peak value of voltage
Effective magnetic volume
Complex impedance
Normalized impedance |Z|
n
= |Z| /N
2
×
ε
(l
e
/A
e
)
5
07/14
Unit
H
H
H
H
H
H
mm
mm
W
W
mW/g
Ω
Ω
Ω
Ω
Ω
Ω
Ω
K/W
Ω
mm
°C
K
°C
s
V
V
mm
3
Ω
Ω/mm
Embedded System
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