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

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 DC SUPPLY TRIAC DC Motor

COMPONENTS R2-68k R3-47K Pot-220k Dc motor Triac Diac Capacitors- C1,C2,C3,C4-.1F Resistors- R1-180Ω R2-68k R3-47K Pot-220k

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