I want to control ST's snubberless triac (T435-800) directly from MCU (STM32F0). According to AN3168 (article 2.4), I've to connect AC main (220V, 50Hz) supply with the control circuit's Vdd. In AN392, I found the same that illustrate triac control with negative power supply, but uses capacitive dropper. Actually, I didn't understand what's going on there after connecting AC main with +5V DC. Why not the control circuit get affected by the AC main? All I want to do the same as AN392, but wants to use SMPS (STEVAL-ISA010V1, based on Viper16). Is it okay to connect SMPS's positive terminal directly to AC main? or Do I need anything else such as diode clipper?