DESIGN AC POWER CONTROL USING TRIAC AND DIAC


CIRCUIT




DESIGN

SUPPOSE THAT TOTAL RESISTANCE IS 56K AT A POT POSITON

THE TIME CONSTANT RC = 56K * .3uF  = 16.8 ms

figure -1 -charging diagram of capacitor


From  figure -1 time constant is the time required to reach 63.2% total voltage

HOW TO FIND FIRING ANGLE

Our input A.C. voltage is 230AC RMS
Then the peak voltage = √2 × Vrms = 325V

then the the voltage at  time constant = 63% of  peak voltage =63% * 325 =204

for diac used is DB3 which has break down voltage of 30V from its datasheet

Vs=Vin(1-e-T/RC)

Vs=Vin(1-e-T/16.8ms)

30=325(1-e-T/16.8ms)
30=325(1-e-T/16.8ms)
0.0923076923076923 =(1-e-T/16.8ms)
e-T/16.8ms =1-0.0923076923076923
e-T/16.8ms  = 0.9076923076923077
eT/16.8ms  =1/0.9076923076923077
eT/16.8ms  =1.10
solving
T/16.8ms  =.1
T=.1 * 16.8ms  
T=1.68ms  

firing angle=( 1.68/10) *180
firing angle =30