CMOS Micropower Step-Up
Switching Regulator
Potted Toroidal Inductors
A typical 1mH, 0.82Ω 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.
MAX630/MAX4193
Diodes
In most MAX630 circuits, the inductor current returns to
zero before L
X
turns on for the next output pulse. This
allows the use of slow turn-off diodes. On the other
hand, the diode current abruptly goes from zero to full
peak current each time L
X
switches off (Figure 1, D1).
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.
Table 1. Coil and Core Manufacturers
MANUFACTURER
MOLDED INDUCTORS
Dale
Nytronics
TRW
POTTED TOROIDAL INDUCTORS
Dale
TRW
Torotel Prod.
FERRITE CORES AND TOROIDS
Allen Bradley
Siemens
Magnetics
Stackpole
Magnetics
T0451S100A
B64290-K38-X38
555130
57-3215
G-41408-25
Tor. core, 500nH/T
2
Tor. core, 4µH/T
2
Tor. core, 53nH/T
2
Pot core, 14mm x 18mm
Pot core, 14 x 8, 250nH/T
2
TE-3Q4TA
MH-1
PT 53-18
1mH, 0.82Ω
600µH, 1.9Ω
500µH, 5Ω
IHA-104
WEE-470
LL-500
500µH, 0.5Ω
470µH, 10Ω
500µH, 0.75Ω
TYPICAL PART NUMBER
DESCRIPTION
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.
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
