Light Dimmer Circuit OR Fan Regulator Circuit OR AC Load Control Using TRIAC - DIAC

• The fan regulator circuit using TRIAC – DIAC is shown in the figure.
• The TRIAC and DIAC are bi – directional therefore they are used for alternating circuit. 
• The R_L is load resistance / lamp or two terminal of single phase winding.
• The charging of capacitor is done through L – R_L – R – C – N path.
• When voltage across capacitor becomes equal to break over voltage of the DIAC, the DIAC turns on. 
• As soon as the DIAC turns on, the discharging of capacitor is done through C – DIAC – G – MT1 – C path. Now the gate terminal of TRIAC gets signal and TRIAC turns on.
• The load resistance complete its path through L – R_L – MT1 – MT2 – N. 
• The charging rate of the capacitor is depends upon the variable resistance R. 
• The firing angle of the TRIAC depends upon variable resistance R. 
• The charging rate of the capacitor is less for higher value of resistance resulting firing angle of TRIAC increases and voltage across load reduces. 
• Similarly the load gets higher voltage for low value of resistance due to less firing angle.  

Finally Remember

High variable resistance – Firing angle increases – Low voltage across load

Low variable resistance – Firing angle decreases – High voltage across load

 LIGHT DIMMER CIRCUIT FIGURE.PDF

CAPACITOR CHARGING - DISCHARGING CIRCUIT.PDF

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