ML4812IP datasheet(11/16 Pages) MICRO-LINEAR

11 / 16 page

ML4812

TYPICAL APPLICATIONS (Continued)

MAGNETICS TIPS

L1 — Main Inductor

As shown in Table 1, one of several toroidal cores can be

used for L1. The T184-40 core above is the most

economical, but has lower inductance at high current.

This would yield higher ripple current and require more

line EMI filtering. The value for RSC (slope compensation

resistor on RAMP COMP) was calculated for the T225-8/

90 and should be recalculated for other inductor

characteristics. The various core manufacturers have a

range of applications literature available. A gapped ferrite

core can also be used in place of the powdered iron core.

One such core is a Philips Components (Ferroxcube) core

#4229PL00-3C8. This is an ungapped core. Using 145

turns of #24 AWG wire, a total air gap of 0.180" is

required to give a total inductance of about 2mH. Since

1/2 of the gap will be on the outside of the core and 1/2

the gap on the inside, putting a 0.09" spacer in the center

will yield a 0.180" total gap. To prevent leakage fields

from generating RFI, a shorted turn of copper tape should

be wrapped around the gap as shown in Figure 11. For

production, a gapped center leg can be ordered from most

core vendors, eliminating the need for the external

shorted copper turn when using a potentiometer core.

COPPER FOIL

SHORTED TURN

0.09" GAP

Figure 11. Copper Foil Shorted Turn

MATERIAL

MANUFACTURER

PART #

TURNS (#24AWG)

Powdered Iron

Micrometals

T225-8/90

200

Powdered Iron

Micrometals

T184-40

120

Molypermalloy

SPANG (Mag. Inc.)

58076-A2 (high flux)

180

Table 1. Toroidal Cores (L1)

T1 — Sense Transformer

In addition to the core type mentioned in the parts list, the

following Siemens cores should be suitable for

substitution and may be more readily available in Europe.

MATERIAL

SIZE CODE

PART #

N27

R16/6.3

B64290-K45-X27

N30

R16/6.3

B64290-K45-X830

The N27 material is for high frequency and will work

better above 100KHz but both are adequate. In addition,

Philips Components (Ferroxcube) core 768T188-3C8 can

be used. Please also refer to the list of core vendors below

SPANG/Magnetics Inc.

1 (800) 245-3984, or

(412) 282-8282

Micrometals

1 (800) 356-5977

Philips Components

(914) 247-2064

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