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DC Inductor Design
Examples

EXAMPLE 1

EXAMPLE 2

Requirements:
45 μH at 7.5
amps DC
(< 1% ripple current)

Requirements:
45 μH at 7.5
amps DC
60μH max at 0 amps DC
(25% saturation max)

(<1 % ripple current)

Determine
importance of the following design considerations: component size,
temperature rise and cost.

Example #1: Design
Priorities
cost
temperature rise
component size

Example #2: Design
Priorities
component size
temperature rise

cost

Select
appropriate materials to be considered.

-26, -52 and -40 Materials
should be considered since the inductor requirements do not limit
swing and these materials are the most cost effective.

-8, -18, -28 and -33 Materials
should be considered because of the limited swing
requirements.

Calculate the
required Energy Storage (1/2 LI2)

1/2 LI2 = (1/2) (45)
(7.5)2 = 1266 μJ

1/2 LI2 = (1/2) (45)
(7.5)2 = 1266 μJ

Select core
size and shape

-26 Material will be used in
this example. Refer to the Energy Storage Table in Core
Loss Increase Due to Thermal Aging, (Figure 4). The T106 size
toroid will be selected in order to keep the winding “simple” and
the temperature rise around 25C°. The E137 is an attractive choice
if bobbin winding is preferred.

The -8 Material is the best
choice since component size is the primary concern.
The Energy
Storage Table Core
Loss Increase Due to Thermal Aging, (Figure 1), indicates that
the T94 size toroid is the smallest core able to meet the energy
storage requirements at < 40C° temperature rise. We must also
check the % saturation curves found in theCore
Loss Increase Due to Thermal Aging text to verify that this core
will be operating at less than 25% saturation.

Determine
number of turns

The curve at the top
of page 40 indicates the T106 will require 217 ampere-turns to
produce 1266 μJ.

Therefore,
NI = 162 / 7.5 = 29 turns

In the case of the E137 core, the curves
indicate that 162 ampere-turns will be required to provide 1266 μJ.

Therefore,
NI = 162 / 7.5 = 22 turns

In the case of the T106 toroidal core, the
“simple” winding limits are close estimates of typical single layer
windings, refer to the Single
Layer Winding Table. This table shows that #7 wire will fit in a
single layer and result in a 25C° temperature rise from the wire. In
the case of the E137, referring to the "Full
Winding" Table indicates that up to #13 wire can be
used.

The curves in theCore
Loss Increase Due to Thermal Aging text indicate that the T94
will be operating at 84.5% of initial permeability (15.5%
saturation) to produce 1266 μJ. Use the following formula to
calculate turns:

Since a “full” winding was required to keep
the temperature rise of the T94 below 40C°, refer to the "Full
Winding" Table. This table indicates that #16 wire should be
used. This table also contains the information necessary to
calculate the DC resistance of a winding.

Determine wire
size

Solution:
T106-26 with 29
turns #17
or E137-26 with 22 turns #14

Solution:
Part number
T94-8/90
with 46 turns
#16

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