Potted Toroidal Inductors

A typical 1mH, 0.82

Ω potted toroidal inductor (Dale TE-

3Q4TA) is 0.685in in diameter by 0.385in high and

mounts directly onto a PC board by its leads. Such

devices offer high efficiency and mounting ease, but at

a somewhat higher cost than molded inductors.

Ferrite Cores (Pot Cores)

Pot cores are very popular as switch-mode inductors

since they offer high performance and ease of design.

The coils are generally wound on a plastic bobbin,

which is then placed between two pot core sections. A

simple clip to hold the core sections together com-

pletes the inductor. Smaller pot cores mount directly

onto PC boards through the bobbin terminals. Cores

come in a wide variety of sizes, often with the center

posts ground down to provide an air gap. The gap pre-

vents saturation while accurately defining the induc-

tance per turn squared.

Pot cores are suitable for all DC-DC converters, but are

usually used in the higher power applications. They are

also useful for experimentation since it is easy to wind

coils onto the plastic bobbins.

Toroidal Cores

In volume production, the toroidal core offers high per-

formance, low size and weight, and low cost. They are,

however, slightly more difficult for prototyping, in that

manually winding turns onto a toroid is more tedious

than on the plastic bobbins used with pot cores.

Toroids are more efficient for a given size since the flux

is more evenly distributed than in a pot core, where the

effective core area differs between the post, side, top,

and bottom.

Since it is difficult to gap a toroid, manufacturers produce

toroids using a mixture of ferromagnetic powder (typically

iron or Mo-Permalloy powder) and a binder. The perme-

ability is controlled by varying the amount of binder,

which changes the effective gap between the ferromag-

netic particles. Mo-Permalloy powder (MPP) cores have

lower losses and are recommended for the highest effi-

ciency, while iron powder cores are lower cost.

Diodes

In most MAX630 circuits, the inductor current returns to

allows the use of slow turn-off diodes. On the other

hand, the diode current abruptly goes from zero to full

To avoid excessive losses, the diode must therefore

have a fast turn-on time.

For low-power circuits with peak currents less than

100mA, signal diodes such as 1N4148s perform well.

For higher-current circuits, or for maximum efficiency at

low power, the 1N5817 series of Schottky diodes are

recommended. Although 1N4001s and other general-

purpose rectifiers are rated for high currents, they are

unacceptable because their slow turn-on time results in

excessive losses.

CMOS Micropower Step-Up

Switching Regulator

_______________________________________________________________________________________

7

MANUFACTURER

TYPICAL PART NUMBER

DESCRIPTION

MOLDED INDUCTORS

Dale

IHA-104

500µH, 0.5

Ω

Nytronics

WEE-470

470µH, 10

Ω

TRW

LL-500

500µH, 0.75

Ω

POTTED TOROIDAL INDUCTORS

Dale

TE-3Q4TA

1mH, 0.82

Ω

TRW

MH-1

600µH, 1.9

Ω

Torotel Prod.

PT 53-18

500µH, 5

Ω

FERRITE CORES AND TOROIDS

Allen Bradley

T0451S100A

Tor. core, 500nH/T

2

Siemens

B64290-K38-X38

Tor. core, 4µH/T

2

Magnetics

555130

Tor. core, 53nH/T

2

Stackpole

57-3215

Pot core, 14mm x 18mm

Magnetics

G-41408-25

Pot core, 14 x 8, 250nH/T

2

Table 1. Coil and Core Manufacturers

Note:

This list does not constitute an endorsement by Maxim Integrated Products and is not intended to be a comprehensive list of

all manufacturers of these components.