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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