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TECHNOLOGY ROBOTICS SOCIETYIndian Institute of Technology, Kharagpur
A TUTORIAL ON ROBOTICS
Motor Drivers
Copyright © Robotix Team, IIT Kharagpur
DC Motor Drivers These are current amplifying circuits A low current control signal is converted into a
proportionally higher current signal that can drive the motor
Power Transistors can switch high currents. The ICmax is usually of the order of Amps as compared to small signal transistors which have ICmax in mA
Example: L293d, L298, ULN2003
Copyright © Robotix Team, IIT Kharagpur
DC Motor Direction Control
H – Bridge Circuit Diagram
S1
S3
S2
S4
M1 2
VCC
Power Transistor Switches
Copyright © Robotix Team, IIT Kharagpur
H – Bridge WorkingS1 S2 S3 S4 Current
DirectionEffect
1 0 0 1 1 to 2 Motor spins forward
0 1 1 0 2 to 1 Motor spins backward
1 1 0 0 - Braking Occurs
0 0 0 0 - Free running
Copyright © Robotix Team, IIT Kharagpur
DC Motor Speed Control Circuit
Input is the operating voltage & control signal Output is a part of the operating voltage depending
upon the control signal
A-
+
DC MOTOR12
OPERATINGVOLTAGE
VOLTAGECONTROLCIRCUIT
CONTROL SIGNAL
Copyright © Robotix Team, IIT Kharagpur
DC Motor Speed Control Cont… Controlling the current by passing it through a variable
resistor is not advisable as it is extremely energy inefficient A trick is done to achieve reduced average power Power is supplied to the motor in short intermittent bursts, as
explained further
Duty Cycle Fundamentals
8s5s
2s
9s
100%80%
4s
10s
100% Duty Cycle
40%60%
7s8s4s
VOLTAGE
------>
40%
40% Duty Cycle
80%
5s9s
20%
1s
80% Duty Cycle
2s 3s3s
20%
6s
TIME------>
4s
20% Duty Cycle
VOLTAGE
------>
8s
2s
100%
9s
VOLTAGE
------>
20%
10s7s
80%
60%
1s
80%
7s
100%
9s6s
1s
5s 5s
TIME------>
40%60%
TIME------>
VOLTAGE
------>
6s3s 10s7s
6s10s
2s 1s
60%
40%
3s
20%
4s
100%
TIME------>
8s
Copyright © Robotix Team, IIT Kharagpur
Duty Cycle Cont… The time period (τ) is the duration after the voltage
waveform repeats itself Duty Cycle is the % time of τ, the voltage is equal to the
operating voltage The average voltage is equal to the ‘Duty Cycle’ % of the
Operating Voltage
Copyright © Robotix Team, IIT Kharagpur
Pulse Width Modulation PWM is a technique using which we can modify the duty cycle
of a waveform depending upon an input control voltage This forms the backbone of our speed control circuit It can be easily implemented using the popular multipurpose
IC 555, used widely for hobby electronics
Copyright © Robotix Team, IIT Kharagpur
Both Speed & Direction Control
NOT GATE
12
Q2
VCC
Q4
Q3
A- +
DC MOTOR
12
AND GATE
1
23
AND GATE
1
23
NOT GATE1
2
R
PWM SIGNAL GENERATOR
SPEED CONTROL SIGNAL
AND GATE
1
23
GND
AND GATE
1
23
Q1
L
