I wanted to try the basic circuit of MOC3051 which is a random phase optoisolator triac driver.
with following parameters:
- Vcc : 3.3v
- Transistor : BD139
- R : 1K
- Triac : BTA40-700b
- Load : Resistive 9.4K
- AC line : from a rotary voltage converter (from 0 - 300 VAC)
I've also implemented zero detection and firing angle handling by a pic microcontroller. The circuit works perfect when the AC LINE voltage is 24VAC and when I checked the signal across the load, it changes perfectly in response to firing angle.
The problem is when I increase the AC LINE voltage up to 90VAC the signal across the load started to vanished at some firing angle and above 100VAC it vanished completely. I've tried different values for R and re-assembled the moc3051 with the new one but nothing's changed.
Do you have any clue why is this happening when AC LINE voltage is increasing while the main purpose of these drivers are to work with 110 - 240vac voltage range?