Speed Control of DC Motor Using TRIAC

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Presentation on IEEE Topic, Speed Control of DC Motor Using TRIAC. 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. 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 with respect to the terminal 1. To successfully trigger a TRIAC, Gate current must come from the main terminal 2 side of the circuit

TRIAC Circuit

The three methods of speed control are

  • Armature voltage controlled
  • Armature resistance controlled
  • Flux controlled

For armature voltage control, the output delivered by the motor(speed) decreases with decrease in applied voltage. The formula for armature voltage control is as given below

armature voltage control


  • 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

  • Today Introduction of IGBT made the speed control of DC motor more feasible
  • Commutation circuit  used in the circuit makes  speed control  less precise
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