Below is a simple dimmer circuit using a triac, a cap and resistors. As you can see, the resistor Poti changes with time and the load current change can be seen in the plot. It seems like one can use this circuit to control a light bulb light or a single phase AC motor according to the simulation.
But in many literature or tutorials, always a diac is connected to the gate of the triac (and sometimes a fuse added to the Line). Here is an example:
My circuit and the circuit in the link have differences. I have the following questions:
1-) Why is a diac used instead of a resistor?
2-) In my circuit I used R1 as 1k value. What is the best value for R1? How can I calculate it?
3-) The circuit in the link has a series 10k resistor next to the potentiometer. Why would that be needed?
4-) Here is another variant: http://www.electronicecircuits.com/electronic-circuits/filament-light-dimmer-circuit What is the job of C2 and R2 here? Suppressing what?