WINDING CONSIDERATIONS

The type and size of the wire used in the winding is also frequency sensitive. This is due to the losses that result in the electronic and magnetic fields emitted from the wire in the winding. As frequency is increased from 100 Khz to 1 Mhz, the resistive eddie-current losses increase and the "skin effect" becomes significant. It is possible to minimize the "skin effect" by dividing the conductor into a bundle of interwoven insulated strands called Litzendraht or Litz wire. The strand diameter is chosen so that the skin effect in the individual strands is negligible.

Litz wire is described as 7/41 (7 strands of 41 AWG), or 15/44 (15 strands of 44 AWG.) and will tend towards larger bundles of smaller strands as frequency is increased. Above 1 Mhz, the advantages of reduced resistance using Litz wire are nullified by the disadvantages of increased capacitive losses created by the stranding.

As the capacitance of adjacent turns as well as the capacitance from the winding to the core becomes significant, stranded wire should be abandoned in favor of heavier solid wire. Thus higher frequency windings will tend towards fewer well spaced turns of larger diameter enamel coated magnetic wire.

The positive influence of Litz wire is demonstrated in the L43 series Q curves With the same number of turns and inductance, the L43-7CT-F-5 with Litz wire has superior Q to the L43-7-CT-F-5 wound with solid wire at approximately 4 Mhz. It is also evident that 50 turns of 15/44 is a more efficient Litz winding than 50 turns of 7/41 on the L57-2-PCT-B-4 tuned to 30 µh at 1.5 Mhz. As the capacitive effects begin to dominate the Litz wire becomes a liability. The exact frequency is dependent on the application but the practical transition is from 1 to 10 Mhz.

The winding table below shows the number of turns of Litz and magnetic wire of different gauges that will fit in each of the Shielded Coil Form's winding area. These turns estimates are for indication only. The actual maximum number of turns will depend on insulation thickness and the winding technique.

TEMPERATURE STABILITY

An important characteristic of iron powder core materials is the outstanding temperature stability. The temperature stability information for each material is listed in parts-per-million-per degree Celsius (ppm/ºC). As an example, the inductance of a 100ppm/ºC material will change by 1% over a temperature change of 100ºC. Figures 4 and 5 plot the temperature stability for iron powder materials as a percentage change in inductance and Q.

The iron powder core materials have excellent temperature stability from -65ºC (-150ºF) up to 125ºC (257). Ferrite materials are more sensitive to temperature and will exhibit changes in inductance and Q from 5 to 10 times greater than iron powder over the same temperature range.

In an iron powder core, inductance will increase gradually as the core materials move from 25ºC to over 100ºC. With continuous operation above 100ºC, inductance and Q will begin to degrade with time. The extent of these changes are dependent on time, temperature, and frequency. Iron powder cores tolerate temperatures down to -65ºC with no permanent effects.

Extended periods of elevated temperature will result in a permanent shift in inductance and Q when the assembly is returned to ambient. For temperature sensitive applications up to 100ºC, this shift can be stabilized by "aging" the core material at 100ºC for a minimum of 48 hours.

 

 

 

WIRE SIZE AWG

20
22
24
26
28
30

WIRE SIZE LITZ

100/43
60/43
40/43
10/40
10/42
15/45

SINGLE LAYER /FULL WINDING

S
F
S
F
S
F
S
F
S
F
S
F

L20











4
4

L30







5
5
5
10
5
10

L32







8
15
10
19
13
25

L33







5
5
5
10
5
10

L333/L335







8
15
10
19
13
25

L337







8
15
10
19
13
25

L39

4
8
6
12
14
27
17
33
22
43
28
106

L3901

4
7
5
9
6
11
8
17
11
38
14
69

L40











4
24

L41







4
8
4
8
4
16

L42

4
4
5
9
7
22
9
30
12
57
15
75

L43

4
8
6
12
8
16
10
20
13
52
17
102

L45

5
8
6
12
8
15
10
19
13
25
17
62

L57

5
10
6
24
8
32
10
60
13
104


WIRE SIZE AWG

32
34
36
38
40
42

WIRE SIZE LITZ

9/45
6/45
5/57
4/48



SINGLE LAYER /FULL WINDING

S
F
S
F
S
F
S
F
S
F
S
F

L20

4
8
4
8
4
32
4
32
4
40
4
112

L30

5
20
5
40
5
60
5
120
5
200
5
300

L32

16
58
21
78
27
147
34
244
43
385
55
594

L33

5
20
5
40
5
60
5
120
5
200
5
300

L333/335

17
62
22
82
27
147
34
244
45
400
55
606

L337

16
58
21
78
27
147
34
244
43
385
55
594

L39

35
134
44
247
55
321
70
655
90
1014
113
1491

L3901

17
87
22
148
28
270
35
399
46
675
58
1045

L40

4
28
4
36
4
48
4
55
4
72
4
96

L41

4
16
4
24
4
32
4
40
4
55
4
64

L42

19
124
24
222
30
345
38
531
50
924
62
1425

L43

21
126
27
216
34
204
42
588
55
990
69
1656

L45

21
78
27
147
34
244
43
385
55
679
70
1107

L57














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