ML4813

13

INDUCTOR INFORMATION

L3 is the flyback inductor and also provides the operating

power for the control circuitry. A gapped ferrite pot core

was chosen for this application for it's modest high

frequency losses with high ripple current operation. Some

possible choices are:

Manufadurer

Part #

Total Gap

Magnetics Inc. F43019

0.05"

32

Phillips

3019 PL00-3F3

0.05"

32

Phillips

3019 PA125-3C8

0.07"

38

The first 2 cores are sold ungapped and require the use of

a .025. spacer to gap the center leg to yield a total gap

length of 0.05". If an ungapped core is used, a "shorted

turn" should be employed as shown in Figure 14 to

prevent radiated EMI. The third core listed is sold with its

center ieg pre-gapped (0.07" total) so that the outside of

the core closes completely, providing shielding without a

#24AWG wire.

Inductors L1 and L2 are constructed using a powdered

iron. This is a suitable material for these inductors since

the high frequency ripple currents (and resulting flux

excursions) are much less severe than for L3. The core

selected is a MicroMetals T68-26D with 80 turns or

#24AWG wire.

Figure 14. EMI Shielding for Ungapped Cores

SHORTED TURN

(COPPER FOIL)

0.25" SPACER

WINDINGS