I built a circuit (like the one below) to control an incandescent light bulb from an Arduino controller for the digital input.
I did not use the zero crossing part of the circuit and mine is running on 120V and a 220 ohm resistor for the triac. My program turns the triac on and off making it dim but also flickers which is an effect I am looking for cause this will be used to simulate a fire. Works great!
My problem happens when I have it plugged into a computer UPS. When I unplug it, and it switches to battery use, the light bulb switches on and stays on. (I swear I had tested this and it didn't do that before.) The circuit works perfectly if I put the UPS back online. The output of the UPS isn't the nice sine wave I expected it to have for a computer back up and, instead, looks like the output of an inverter I tried before; very spiky. I also measure the voltage dropping to around 90V with a meter.
The whole purpose of this is to make this circuit be portable inside a bucket with a UPS powering it and now I'm stuck and running out of time. Does someone have a fix and possibly a lesson in the process? (I've been out of electronics for a while and not a power electronics guy in the first place.)
EDIT: It is not necessary for me to use this circuit exactly. I once thought of using a FET and driving the bulbs directly from an inverter but my UPS idea solved the problem of charging the battery. But I have the same problem in that I have not done any circuit design in over 10 years.
Best Answer
Your UPS likely has a square (non-sinewave) output. The square output likely exceeds the dv/dt rating of the triac, causing it to turn on. You might want to consider a snubbing network to reduce the dv/dt transients.