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2003 Microchip Technology Inc. DS00898A-page 1
M
AN898
INTRODUCTION
Electronic motor control for various types of motors
represents one of the main applications for MOSFET
drivers today. This application note discusses some of
the fundamental concepts needed to obtain the proper
MOSFET driver for your application.
The bridging element between the motor and MOSFET
driver is normally in the form of a power transistor. This
can be a bipolar transistor, MOSFET or an Insulated
Gate Bipolar Transistor (IGBT). In some small
Brushless DC motor or stepper motor applications, the
MOSFET driver can be used to directly drive the motor.
For this application note, though, we are going to
assume that a little more voltage and power capability
is needed than what the MOSFET drivers can handle.
The purpose of motor speed control is to control the
speed, direction of rotation or position of the motor
shaft. This requires that the voltage applied to the
motor is modulated in some manner. This is where the
power-switching element (bipolar transistor, MOSFET,
IGBT) is used. By turning the power-switching ele-
ments on and off in a controlled manner, the voltage
applied to the motor can be varied in order to vary the
speed or position of the motor shaft. Figures 1
through 5 show diagrams of some typical drive config-
urations for DC Brush, DC Brushless, Stepper, Switch
Reluctance and AC Induction motors.
FIGURE 1: Drive Configuration for a DC
Brush Motor.
FIGURE 2: Drive Configuration for a DC
Brushless Motor.
FIGURE 3: Drive Configuration for a
4-Wire Stepper Motor.
Author: Jamie Dunn
Microchip Technology Inc.
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Determining MOSFET Driver Needs for
Motor Drive Applications
