RMS Voltage Control Circuit with Opto Triac MOC3021 and BT136

Triac is a power electronic component that conducts in both directions when triggered through gate. Figure below shows a generic working of triac.As it can be seen that at time t1, angle of sinusoid is 45' which means that if we triggered triac at this angle i-e at 45', only shaded blue area will pass through the triac and hence through the load. Observe that shaded blue are has RMS Voltage less than the pure sinusoid. This is the basic principle by which RMS Voltage control is accomplished. Firing needs a small pulse at gate that can be give through microcontroller also. Similarly at firing angle 90' (firing angle is an angle with reference zero crossing at which the triac is triggered using gate pulse) , only red part of sinusoid will pass through the triac giving us the RMS 110V for 220V.

 

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