Specifications

Motor Control
Overview
www.digikey.com/maxim-industrial 95
Overview
Electric motors consume almost 50%
of the world’s electricity. With the
cost of energy rising steadily, industry
is focused on replacing inefficient
constant-speed motors and drives
with microprocessor-based, variable-
speed drives. This new motor-control
technology will reduce energy
consumption by more than 30%
compared to the older drives. While
these variable-speed controllers add
cost to a motor, the forecasted
energy savings and increased motor
functionality should easily offset
those initial expenses within a
few years.
Popular motor designs
The DC motor, brushless DC, and
AC induction motor are the popular
motor designs used in today’s indus-
trial applications. Each of these
motor types has its own unique
characteristics, but they all operate
on the same basic electromagnetic
principle: when a conductor carrying
current, such as a wire winding, is
located in an external magnetic field
perpendicular to the conductor, then
the conductor will experience a force
perpendicular to itself and to the
external magnetic field.
DC motors: low cost and accurate
drive performance
A DC motor was among the first motor
types put to practical use, and it is still
popular where low initial cost and
excellent drive performance are
required. In its simplest form, the stator
(i.e., the stationary part of the motor) is
a permanent magnet, and the rotor
(i.e., the rotating part of the motor)
carries an armature winding connected
to a mechanical commutator which
switches current on and off to the
winding. The magnet establishes the
field flux which interacts with the
armature current to produce the
electromagnetic torque, thereby
enabling the motor to perform work.
The motor’s speed is controlled by
adjusting the DC voltage applied to
the armature winding.
Depending on the application, a
full-bridge, half-bridge, or just a
step-down converter is used to drive
the armature winding. The switches
in these converters are pulse-width
modulated (PWMed) to achieve the
desired voltage. Maxim’s high-side or
bridge-driver ICs like the MAX15024/
MAX15025 can be used to drive the
FETs in the full- or half-bridge circuit.
DC motors are also widely used in
servo applications where speed and
accuracy are important. To meet
speed and accuracy requirements,
microprocessor-based closed-loop
control and information about rotor
position are essential. Maxim’s
MAX9641* Hall-effect sensor provides
information about rotor position.
DC-DC
POWER
TEMP
SENSOR
SUPERVISORS
HALL-EFFECT SENSOR
RESOLVER
ENCODER
RS-485
= MAXIM SOLUTION
CURRENT-
SENSE
AMPLIFIER
CURRENT-
SENSE
AMPLIFIER
ADCs
THREE-PHASE BRIDGE
MOTOR
MICROCONTROLLER
SPEED
DIRECTION
TORQUE
GATE
DRIVER
LOGIC
Block diagram of a typical industrial motor control.
For a list of Maxim’s recommended motor-drive solutions, please go to: www.maxim-ic.com/motordrive.