UCC29421, UCC29422, UCC39421, UCC39422

MULTIMODE HIGHFREQUENCY PWM CONTROLLER

SLUS246C − OCTOBER 1999 − REVISED FEBRUARY 2005

29

POST OFFICE BOX 655303

APPLICATION INFORMATION

selecting the inductor

The inductor must be chosen based on the desired operating frequency and the maximum load current. Higher

frequencies allow the use of lower inductor values, reducing component size. Higher load currents require larger

inductors with higher current ratings and less winding resistance to minimize losses. The inductor must be rated

for operation at the highest anticipated peak current. Refer to equation (8) and equation (12) to calculate the

value. Some manufacturers rate their parts for maximum energy storage in microjoules (

µJ). This is expressed

by:

E

+ 0.5

L

I

PEAK

2

(21)

where E is the required energy rating in microjoules. L is the inductor value in microhenries (

µH) (with current

inductor ratings are sometimes specified is the maximum volt-seconds applied. This is given simply by:

E

T

+

V

IN

D

f

(22)

where ET is the required rating in V-

frequency in MHz. Refer to equations (7) and (11) to calculate the duty cycle for a CCM boost or flyback

converter.

In any case, the inductor must use a low loss core designed for high-frequency operation. High-frequency ferrite

cores are recommended. Some manufacturers of off-the-shelf surface-mount designs are listed in Table 3. For

flyback and SEPIC topologies, use a two-winding coupled inductor. SEPIC designs can also use two discrete

inductors.

Table 3. MT COMMERCIAL INDUCTOR MANUFACTURERS

Coilcraft Inc.

⋅ (800) 322−2645.1102 Silver Lake RD, Cary, IL 60013

Coiltronics Inc.

⋅ (407) 241−7876 6000 Park of Commerce Blvd, Boca Raton, FL 33487

Dale Electronics, Inc.

⋅ (605) 665−9301East Highway 50, Yankton, SD 57078

Pulse Engineering Ltd.

⋅ (204) 633−4321300 Keewatin Street, Winnipeg, MB R2X 2R9

Sumida

⋅ Voice (65) 296−3388 ⋅ Fax (65) 293−3390 Block 996, Bendemeer Rd., #04−05/06 Singapore 33944

BH Electronics

⋅ (612) 894−9590 12219 Wood Lake Drive, Burnsville, MN 55337

Tokin America Inc.

⋅ (408) 432−8020155 Nicholson Lane, San Jose CA 95134