This is a circuit from a Texas Instrument data sheet
It seems fine when everything is working, but what if the discrete triac becomes disconnected at the top end (at the load), or suffers an internal failure with the same result?
When the optocoupler is turned on, the load current will attempt to pass through the 1.2k resistor, the optocoupler's triac, and the gate of the discrete triac. The resistor will limit it to 200mA, but that's twice the rated continuous current of the optocoupler's triac. It also considerable exceeds the permitted gate current of the discrete triac.
So then the question is which will fail first. If it's the optocoupler's triac, how sure can we be that the isolation barrier won't be compromised in the process?
I've considered putting a 50mA non-ressetable fuse in series with the
1.2K resistor.Any thoughts?
Sylvia.