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}
e^T/16.8ms  =1/0.9076923076923077
e^T/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