Hi, I really need some help here. I am using PIC16F628a's PWM signal to change speed of AC (120V, 60Hz) blower. At low speed, the blower tends to "hesitate". On the scope, I found that the chopped part of the AC wave is always changing, which makes the current fluctuate. I guess it is because my PWM is not synchronized to the AC frequency so that the duration from zero cross to PWM activation pulse for the Triac is changing. Can anyone tell me if it is required to synchronize them? Many thanks!