Synchronous! non-synchronous triggering is possible in triacs by applying AC power line voltage to the gate of the triac. In synchronous switching, the triac turns on at the same point in each AC half cycle just after the zero crossing point. In non-synchronous switching, the switching is not always synchronised to the fixed points of AC cycle and RFI will be very high particularly at the point of initial power-'on.' The low RFl in synchronous switching makes it advantageous especially for higher power load circuits. Fig. 8 shows two methods of triac switching using AC line voltage.

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Transformer-derived DC or battery power is used in DC triggering through a transistor switch or by electronic devices like lCs. If a transistor is used, external sensor circuits can be interfaced and the load switch-' on' can be controlled by external parameters like light and heat. The simplest way of DC triggering is shown in.