Simplified Inductor Design

3.4 Designing Inductors and Transformers

3.4.1 Simplified Inductor Design

Once the desired inductance value L and peak current IpK are found using the equations of Section 3.2, the first step in simplified inductor design is to calculate the Lj² product in millijoules (mH x A² = mJ). This is actually twice the maximum

O Table 3-5. Typical low-cost inductors (Maxim Seminar Applications Book, 1989, p. 91)

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• SMPS AVERAGING FILTER '*> • CHARACTERIZED FOR GENERAL PURPOSE USE, AND RIPPLE FILTERS • SINGLE LAYER DESIGNS • CAN BE USED AS DIFFERENTIAL MODE INDUCTORS IN EMI FILTERS 3 • MOUNTING PACKAGE AVAILABLE ON REQUEST • DESIGNER KIT AVAILABLE Reference Operating Values Part Number 1 51591 92100 92101 92102 92103 92104 | 92105 _

Klip iMÉMCtaWCI Mount Typical 1« Option (μ Hy)<» (AMPS) 20 2.0 K 25 2.5 K 50 2.5 K 100 2.5 K 35 2.5 K 70 3.0 K 145 3.0

ET., (V^Stc) 52 30 50 90 55 85 140

Design Control Values (2) No O.C ^M (μ Hy) . im 32.8 20.7 45.7 94.1 28.4 61.0 141.8

1000 Hz Tost Volts NoD.C. 0034 0023 .0047 .0094 .0037 .0076 .015

OCR Coil Klip (OHMS) Size Mount Max Code Package .06 H .04 A KM1 .07 B KM2 .10 C KM3 .04 B KM2 .05 C KM3 .08 D KM4

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K> Table 3-6. Miniature high-current chokes (Maxim Seminar Applications Book, 1989, p. 92) QUALITY COILS SINCE 1946 258 East Second Street Mineota, New York 11501-350

(WCAEmL-gjRNS )

Area Code 516 746-2310

MINIATUR E HIG H CURREN T CHOKE S

1.0μΗ - 100mH. 10% Tolerance. Recommended Mounting Pitch — .80" TYPE 7070 TYPE 7060 (EPOXY ENCAPSULATED VERSION) #22 AITOeeje Tinned Copper #22 AWQ Bart TWvMd Copper

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£» Table 3-7. High-current chokes (Maxim Seminar Applications Book, 1989, p. 93) QUALITY COILS SINCE 1946

C« B CADDELL-BURNS) )

258 East Second Street Mineola. New York 11501-3508 Area Code 516 746-2310

HIG H CURREN T CHOKE S

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NOTES: (FOR BOTH TYPES) 4. Dielectric Withstanding Voltage — 1000 VRMS. 1. Inductance (Ls) measured on General Radio 1650B Impedance 5. Operating temperature range — 55° to + 105°C. Bridge at 1 KHz. 6. Materials 2. Current rating (Rated IDC) is based on 0.5 watt power dissipation for approximately 20°C temperature rise. Depending on the appli­ cation, these units may be operated at up to twice the rated current. 3w Incremental current (INCR I) is the minimum current at which the inductance will be decreased by 5% from its initial (zero-DC) value. Coil Form: Ferrite. Cover: TYPE 6860 - Polyester alpha-cellulose. Coating: Polyurethane per MIL-1-46056. TYPE 6870- Cover & Coating: Epoxy encapsulated. Magnet Wire: Per FED SPEC J-W-001177/9 (MIL-W-583 Type B

STANDARD VALUES: (Eloctrlcal characteristic· ara Identical for both type·. Other vateiee are available on epeelal order. Dit* M«. —01 —02 —03 —04 -45 —06 —07 —0· -09 —10 —11 —12 —13 —14 —15 —16 —17 —18 —19 —20 —21 —22 -23 —24 —25 —26 —27 -21 —29 —30 -31 NtMlaäT" laëactaaca 10 MH

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Mai. 0CI OtMS .023 .025 .030 .032 .035 .038 .043 .047 .054 .060 .068 .073 .098 .14 .18 20 28 .31 .35 .38 .44 48 63 .87 96 1.3 1.4 1.7 2.3 2.6 3.5

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latte IOC ma 4600 4500 4100 3900 3700 3600 3400 3200 3000 2900 2700 2600 2300 1900 1700 1600 1400 1300 1200 1100 1050 1000 890 760 720 620 600 540 470 440 L 380

INCH I ma 1 3200 2900 2600 2400 2200 2000 1 1800 1700 1500 1400 1200 1100 1000 930 830 760 680 620 560 510 460 430 390 350 320 290 260 240 220 190 180 150 50

Data Na. —32 —33 -34 —35 -36 —37 -38 —39 —40 —41 —42 —43 —44 —45 —46 —47 —48 —49 —50 —51 —52 —53 —54 —55 —56 -57 -58 —59 —60 1 —61

MaaMMf Indactaact 3 9mH 4.7 5.6 6.8 82 10 12 15 18 22 27 33 39 47 56 68 82 100 120 150 180 220 270 330 390 470 560 680 820 1.0 H

Mai. 0C8 OtMS 3.8 4.3 5.6 6.3 8.6 9.7 11 15 20 24 26 35 38 50 55 76 86 99 ua 200 220 300 320 420 480 670 736 870 950 1100

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lattt I0C •a 360 340 300 280 240 220 210 180 160 140 130 120 110 100 95 81 76 71 67 50 48 41 40 35 32 27 26 24 23 21

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Table 3-8. Inductor and transformer suppliers (Maxim Seminar Applications Book, 1989, pp. 88-89)

INDUCTO R AN D TRANSFORME R SUPPLIER S

AIE Magnetics 701 Murfreesboro Rd. Nashville, TN 37210 TEL 615-244-9024

AIE makes a variety of coils and transformers. Their full line catalo lists a variety of inductors. Catalog 5 lists many transformer designed for flyback converters up to 50 watts. Catalog 3 lists man coils types: slugs, toroids, pot cores, etc. BH Electronics 12219 Wood Lake Dr. Burnsville, MN 55337 TEL 612-894-9590 FAX 612-894-9380

Coils and transformers from miniature surface mount up throug 10's of watts. Caddell-Burns 40 East Second Street Mineola, NY 11501 TEL 516-746-2310

Caddell-Burns has many standard coils in their 6860 and 707 series which are suitable for use with Maxim's DC-DC converters 7070 series coils have high current ratings for their size. Efficien cies that match toriods can be acheived. Dale Electronics East Highway 50 Yankton, SD 57078 TEL 605-665-9301

Standard toroidal inductors in moulded PC mount packaging.

Gowanda Electronics Corp. 1 Industrial Place Gowanda, NY 14070 TEL 716-532-2234 J.W. Miller 19070 Reyes Ave. P.O. Box 5825 Rancho Dominguez, CA 90224 TEL 213-537 5200 FAX 213-631-4217 Nytronics Components Group, Inc Orange Street Darlington, SC 29532 TEL 803-393-5421 Pulse Engineering P.O. Box 12235 San Diego, CA 92112 TEL 619-268-2400 FAX 619-268-2515 Prem Magnetics 3521 North Chapel Hill Rd. McHenry, IL 60050 TEL 815-642-3763 TWX 910-642-3763

Gowanda makes coils ranging from surface mount devices u through high power toroids, and also has many inductors woun on cylindrical ferrite bobbins. They make transformers in pot cores E cores, and toroids. Miller has standard coils and toriods at low cost, however, avoi the tiny moulded chokes. The series resistance and current rating of the small moulded parts are generally not adequate for DC-D applications except in extremely low power applications (mA). Small moulded inductors which generally do not have adequat current capability for DC-DC circuits except in very low current ap plications (mA). Pulse Eng. supplies a line of low cost toroids, as well as mounte and moulded toriods. A toroid sampler kit, #845, is useful fo prototyping designs. Custom transformers are also available. Prem supplies low cost, high current toroids.

o 00 Table 3-9. Pot and toroid core suppliers (Maxim Seminar Applications Book, 1989, pp. 89-90)

POT-COR E AN D TOROID-COR E SUPPLIER S

Allen-Bradley Magnetic Products 5900 N. Harrison St. Shawnee, Oklahoma 74801 TEL 405-275-2100/TLX 796208

Publication MPCC contains information on both soft/linear ferrit and permanent magnetics. The key section is the "W5" sectio which provides info on their optimum material for DC-DC con verters, as well as pot cores and toroids made from this material Arnold Engineering Company 300 West Street Marengo, Illinois 60152 TEL 815-568-2000 TWX 910-642-2790

Arnold makes cores in both iron powder and molypermalloy pow der (MPP). Ferroxcube 5083 Kings Highway Saugerties, NY 12477 TEL 914-246-2811 TWX 510-247-5410

Ferroxcube's Linear Ferrite Materials and Components catalog list a wide variety of cores: toroids, pot cores, square cores, EP, EC etc. The catalog has complete data on the cores and material, bu little applications information. Magnetics Div. of Spang and Co. 900 E. Butler Rd. P.O. Box 391 Butler, PA 16003 TEL 412-282-8282 TWX 710-373-3821

Magnetics has a complete line of magnetic materials: The ferrite and MPP cores are the most useful for DC-DC converters. A com plete catalog/binder with both inductor design information and com plete product data is available. All of the standard core shapes ar available: pot cores, EE, El, bobbin, toroids, etc. The catalog con tains useful coil design information.

Micrometals, Inc. 1190 N. Hawk Circle Anaheim, CA 92807 TEL 714-630-7420 TWX 910-591 -1690 Siemens Components Inc. Special Products Division 186 Wood Avenue South Iselin, NJ 08830 TEL 201-321-3400 Permag Inc., Regional offices: Atlanta Boston Chicago Dallas Colorado Los Angeles Minneapolis San Francisco Toledo NY/LI

404-448-4998 617-273-2890 312-956-1140 214-699-1121 303-693-6612 714-952-2091 612-934-4635 408-738-1080 419-385-4621 516-822-3311 Cores Unlimited, Inc. 8311 Westminster Ave. Suite 340F Westminster, CA 92683 TEL 714-894-3062 800-772-CORE FAX 714-895-4502

Low cost iron powder cores in toroids, E cores, and bars. Thes are lower cost than MPP or ferrite, but have lower efficiency. The "Ferrite Cores and Hardware" short form catalog provides in formation on pot cores from 3.3x2.6mm to 41x25mm; toroios fro 2.5mm to 34mm diameter, and a wide variety of other shapes suc as E and RM. Permag is a Distributor of Magnetic Cores for Allen- Bradley, Stack pole, Siemens, and Krystinel. Cores Unlimited is an authorized distributor of magnetic cores fo Hitatchi and Siemens. They also handle cores from several othe manufacturers.

amount that the inductor core must store (E = Lj²/2), but it is the quantity specified in most pot-core and toroid literature.

With Lj² established, select the core size from the pot-core selection guide in Fig. 3-4. Find Lj² on the x axis, and draw a vertical line up from that point to the lowest intersecting diagonal line. Read the inductance factor, AL, from the y axis.

The diagonal line and the corresponding value from the y axis represent the smallest core size and the maximum AL that may be used (AL is the inductance per turns squared for the core). This means that any core of that size, with an AL less than the y-axis value, will not saturate. Also, any other core that intersects the Lj² line is us­

able if its AL is less than the y-axis value. Of course, if a core with too small an AL is selected, then the needed number of turns may not fit on the core.

Typically, in flyback transformers, wire size, resistance, and "fitting" the turns on the core are usually not a problem (because the specified inductances are small, so few turns are needed). This often allows the use of significantly smaller AL val­

ues than provided by the graph of Fig. 3-4. In turn, the smaller AL values reduce core losses. However, the gain must be weighed against the increased wire losses.

With AL established, the number of turns of wire, N, to be wound on the core for the desired inductance is:

N = 31.6V(L/AL), where L is the inductance in μΗ.

With the number of turns established, we now want the largest wire that will fit on the core (within reason) to minimize the DC resistance. The available winding area, Aw, can be found in the core data or with the ferrite pot-core winding dimen­

sions on Table 3-10.

With the number of turns (N) and the winding area (Aw) established, the next factor to find is the number of turns/cm², or T. T must be greater than N divided by Aw

and can be found on Table 3-11. Use a wire size that has an adequate value for T.