®
VERSA-PAC
®
Inductors and Transformers
(Surface Mount)
HOW TO USE MULTIPLE WINDINGS
Discrete inductors combine like resistors, when connected in series or parallel. For example, inductors in series add and
inductors in parallel reduce in a way similar to Ohm’s Law.
L
Series
= L1 + L2 + L3...Ln
L
Parallel
= 1/
[
1/L1 + 1/ L2 + 1/ L3....1/Ln
]
Windings on the same magnetic core behave differently. Two windings in series result in four times the inductance of a
single winding. This is because the inductance varies proportionately to the square of the turns.
Paralleled
VERSA-PAC
windings result in no change to the net inductance because the total number of turns remains
unchanged; only the effective wire size becomes larger. Two parallel windings result in approximately twice the current
carrying capability of a single winding. The net inductance of a given
PCM
configuration is based on the number of
windings in series squared multiplied by the inductance of a single winding (L ). The current rating of a
PCM
configuration
is derived by multiplying the maximum current rating of one winding (I ) by the number of windings in parallel. Examples
of simple two-winding devices are shown below:
BASE
BASE
Series Connected
(2 Windings)
Parallel Connected
(2 Windings)
10µH
1 Amp
10µH
1 Amp
10µH
1 Amp
10µH
1 Amp
L
TOTAL
= L
BASE
x S I
MAX
= I
BASE
x P
= 1 Amp x 1
= 10 µH x 2
= 1 Amp
= 40 µH
2
2
L
TOTAL
= L
BASE
x S
I
MAX
=
I
BASE
x P
= 10 µH x 1
= 1 Amp x 2
= 10 µH
= 2 Amps
2
2
Where:
L
BASE
=
Inductance of a single winding
P = Number of windings in parallel (use 1 with all windings in series)
S = Number of windings in series
I
BASE
=
Maximum current rating of one winding
COOPER [ COOPER BUSSMANN, INC. ]
