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SPEED CONTROL OF
DC MOTOR USING
TRIAC
INTRODUCTION
 DC motors are widely used in industry because of
its low cost, less complex control structure and
wide range of speed and torque
With the the increasing use of power semicondutor
units, the speed control of DC motor is increasingly
getting sophisticated and precise.
TRIAC
 A triac is a bidirectional thyristor with three
terminals
 Its three terminals are designated as MT1(main
terminal 1),MT2 & gate by G
 Triac can be turned on in each half cycle of the
applied voltage by applying a positive or negative
voltage to the gate w.r.t terminal MT1
 To successfully trigger a triac,gate current must
come from the main terminal 2(MT2) side of the
CIRCUIT SYMBOL
BT136
SPEED CONTROL
The three methods of speed control are
 Armature voltage controlled
 Armature resistance controlled
 Flux controlled
ARMATURE VOLTAGE
CONTROL
 The output delivered by the motor(speed) decreases
with decrease in applied voltage
BLOCK DIAGRAM
TRIAC
DC Motor
DC SUPPLY
COMPONENTS
 Dc motor
 Triac
 Diac
 Capacitors-
C1,C2,C3,C4-.1F
 Resistors-
R1-180Ω
ADVANTAGES
 In earlier days speed of the dc motor was controlled
using resistor which resulted in power loss but
introduction of triac eliminated the power loss
 Armature voltage control method gives good speed
regulation and high efficiency
 Gives a large speed range with any desired number of
speed points
DISADVANTGE
 Today Introduction of IGBT made the speed control of
dc motor more feasible
 Commutation circuit used in the circuit makes speed
control less precise