I'm trying to create a dimmer that uses an IC to control the triac firing. My understanding is that I need a random phase optocoupled triac driver. However I need to know when the zero crossing is on the IC. I've seen circuits similar to below for optocouplers
Here's where I'm confused, every depiction of an optocoupler shows the two left pins as an anode and cathode, which brings me to my first questions.
Does the DC side only conduct on the half wave? Or is it actually two parallel diodes in opposite directions? If that's the case,
Could I implement my zero crossing detection by having the far right wire go to an external interrupt on my IC and just switch between positive and negative edge trigger, causing an interrupt when it crosses zero because it switches between VCC and GND going to the pin?
Wouldn't the Vf of the diode cause issues because it wouldn't conduct until slightly past the zero crossing whenever the AC crosses the Vf?
Next, regarding noise, I've seen several ways of minimizing this.
Is it better to turn on at the zero crossing and shut off midwave or turn off at the zero crossing and turn on midwave as far as minimizing noise?
Sometimes I see inductors, sometimes I see RC snubbers in dimming circuits. Most online circuits show the RC snubber, but the ETC Sensor dimmers I've worked with have very large inductors (though I don't know if there's also an RC). Is there a reason to use one over the other/both?
When choosing a size for the inductor,
- Do triacs have a rated switching speed? (e.g. to calculate the dI/dt across the inductor, do I assume it's an instantaneous change or is there a rated 'speed' for a triac? The only dv/dt ratings I've seen on a triac have to do with protecting it from false firing.
Thank you so much