1. SPEED CONTROL OF DC MOTOR USING TRIAC

2. 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.

3. 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

4. CIRCUIT SYMBOL

5. BT136

6. SPEED CONTROL The three methods of speed control are
Armature voltage controlled
Armature resistance controlled
Flux controlled

7. ARMATURE VOLTAGE CONTROL
The output delivered by the motor(speed) decreases with decrease in applied voltage

8. BLOCK DIAGRAM
DC SUPPLY
TRIAC
DC Motor

11. 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

12. 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

13. 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