Specifications

118 Control and Automation Solutions Guide
Figure 1. Two control techniques for BDC motors. The upper diagram shows a variable voltage technique that is high efficiency due to the switching power supply. The lower diagram
shows the PWM technique that can be lower cost if the motor is rated for the full supply voltage.
SWITCH
DEBOUNCER
µP
START
CONTROL PANEL
VARIABLE VOLTAGE TECHNIQUE
STOP
FASTER
SLOWER
DISPLAY
DRIVER
DISPLAY
SUPERVISOR
V
CC
V
CC
I
OUT
V
CC
BUCK
V
DC
V
DC
DAC
ADC
CURRENT-
SENSE AMP
OP AMP
MOTOR
SPEED,
POSITION
SENSOR
TEMPERATURE
SENSOR
UART
SENSOR
INTERFACE
BUCK
SHDN FB
ISOLATION TRANSCEIVER
FIELDBUS
MOTOR
SWITCH
DEBOUNCER
START
CONTROL PANEL
PWM TECHNIQUE
STOP
FASTER
SLOWER
DISPLAY
DRIVER
DISPLAY
SUPERVISOR
V
CC
V
DC
V
CC
V
CC
BUCK
V
DC
MOTOR SPEED,
POSITION
SENSOR
TEMPERATURE
SENSOR
GATE
DRIVER
SENSOR
INTERFACE
UART ISOLATION TRANSCEIVER
FIELDBUS
MOTOR
ADC
µP
MOTOR
as a part of normal motor operation.
This, in turn, creates EMI/RFI and small
amounts of ozone. Where system cost
is a priority, BDC motors are a low-
cost solution. While their eciency
is generally lower than brushless
DC (BLDC) motors, they approach
equality under high-load conditions.
Controllers for BDC Motors
The only variable available to control
the speed of a BDC motor is the supply
voltage. The voltage can be varied
or a xed voltage can be pulsed with
variable duty cycle. For high eciency
in a variable voltage approach, a switch-
mode power supply is required. Most
designers are abandoning linear voltage
regulation because of its inherently
low eciency. One way to realize a
variable-voltage power supply from
any switch-mode voltage regulator is to
inject or extract current into or out of
its feedback node using a current sink/
source DAC. See Figure 1. When the