LIGHT DIMMER USING TRIAC-DIAC

SOMETHING ABOUT CIRCUIT:

The intensity of LAMP source can be varied over wide range by using a TRIAC. As we know a TRIAC is a bidirectional device which requires a triggering pulse at its gate to perform both half cycles. A DIAC is used in the circuit for triggering purpose, DIAC triggers the TRIAC.

COMPONENTS LIST:

  1. LAMP (LOAD)
  2. VARIABLE RESISTOR (100K)
  3. RESISTOR (46/56K OHM)
  4. DIAC (DB3)
  5. TRIAC (BT136)
  6. CAPACITOR (0.33 micro farad)
  7. LAMP SOCKET

WORKING:

In this circuit a lamp acts as load, a potentiometer (P) is used for varying the firing angle of the TRIAC and a fixed resistor (R) at which the potentiometer is at zero resistance value.The resistance value by the potentiometer decides the charging time constant which required by the capacitor.If the resistance is low, the firing angle as well as the charging time of the capacitor is low and if the resistance is high, then it will take more time to charge.The TRIAC is a undirectional device it consist of three pins namely 1st-MT1, 2nd-MT2 and 3rd-Gate(G).The Gate terminal i.e 3rd pin is directly short with the diode. As the TRIAC requires a triggering pulse to perform its operation here a DIAC provides triggering pulse to the TRIAC when the voltage on DIAC reaches the breakdown voltage.As soon the TRIAC is turned ON the voltage across the capacitor decreases rapidly to zero value.The TRIAC is now turned ON with the firing angle.During the positive half cycle of AC signal the capacitor charges with upper plate positive(+) and lower plate negative(-).Hence the firing angle is (π-α).The intensity of lamp will depend upon the value of firing angle of the TRIAC. Less the value of the firing angle (α) of the TRAIC, more will be the voltage across the lamp and hence more will be its intensity of illumination and vice-versa.

 

 

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