RC4190
PRODUCT SPECIFICATION
3. Note the approximate air gap at I
for the selected
Compare the waveform you see to those pictured in
Figure 28.
MAX
core, and order the core with the gap. (If the gapping is
done by the user, remember that a washer spacer results
in an air gap of twice the washer thickness, because two
gaps will be created, one at the center post and one at the
rim, like taking two bites from a doughnut.)
Check for saturation at the highest expected ambient
temperature.
7. After the operation in circuit has been checked,
reassemble and pot the core using a potting compound
recommended by the manufacturer.
4. If the required inductance is equal to the indicated value
on the graph, then wind the core with the number of
turns shown in table of sizes. The turns given are the
maximum number for that gauge of wire that can be
easily wound in the cores winding area.
If the core material differs greatly in magnetic character-
istics from the standard power material shown in Figure
22, then the following general equation can be used to
help in winding and gapping. This equation can be used
for any core geometry, such as an E-E core.
5. If the required inductance is less than the value indicated
on the graph, a simple calculation must be done to find
(1.26)(N2)(Ae)(108)
LX = -----------------------------------------------------
g = (le) ⁄ (ue)
the adjusted number of turns. Find A (inductance
L
index) for a specific air gap.
L(indicated)
Where: N = number of turns
--------------------------------- = AL
Turns2
Ae = core area from data sheet (in cm2)
le = magnetic path length from data sheet (in cm)
ue = permeability of core from manufacturer's graph
g = center post air gap (in cm)
in Henrys/turn2
Then divide the required inductance value by A to give
L
the actual turns squared, and take the square root to find
the actual turns needed.
Manufacturers
Below is a list of several pot core manufacturers:
L(required)
ActualTurns = ------------------------------
AL
Ferroxcube Company
5083 Kings Highway
Saugerties, NY 12477
If the actual number of turns is significantly less than the
number from the table then the wire size can be
increased to use up the left-over winding area and
reduce resistive losses.
Indiana General Electronics
Keasley, NJ 08832
6. Wind and gap the core as per calculations, and measure
the value with an inductance meter. Some adjustment of
the number of turns may be
Siemens Company
186 Wood Avenue South
Iselin, NJ 08830
necessary.
The saturation characteristics may be checked with the
inductor wired into the switching regulator application
circuit. To do so, build and power up the circuit. Then
(recommend Tektronix P6042 or equivalent) around the
inductor lead and monitor the current in the inductor.
Draw the maximum load current from the application
circuit so that the regulator is running at close to full
duty cycle.
Stackpole Company
201 Stackpole Street
St. Mary, PA 15857
TDK Electronics
13-1-Chome
Nihonbaski, Chuo-ku, Tokyo
Improper Operation
(Waveform is Nonlinear, Inductor
Is Saturating)
Proper Operation
(Waveform is Fairly Linear)
I
MAX
I
MAX
0
0
65-3464-08
Figure 28. Inductor Current Waveforms
21
RAYTHEON [ RAYTHEON COMPANY ]
