I'm looking (again) at a dimming circuit based around the OnSemi FL5150/FL5160 dimmer on a chip IC.
The datasheet shows example circuits with three resistors connected to the mains supply load/neutral: two to provide over current sensing and one to provide zero cross detection.
Given that the "GND" reference voltage for the IC is tied to the mid point (common source) of the back-to-back switching mosfets, what voltage would there be across these three resistors ?
I'm thinking when the mosfets are off, there will be a max of 120V * 1.4 between "GND" and Line Hot. And when the switch is on the "GND" reference point will float 17v (the internally provided Vs) below Line Hot.
In this case resistors will need to be rated for 170V (or 325V for 230V ac operation) plus any required safety allowances.
Does this sound reasonable ?
The datasheet shows example circuits with three resistors connected to the mains supply load/neutral: two to provide over current sensing and one to provide zero cross detection.
Given that the "GND" reference voltage for the IC is tied to the mid point (common source) of the back-to-back switching mosfets, what voltage would there be across these three resistors ?
I'm thinking when the mosfets are off, there will be a max of 120V * 1.4 between "GND" and Line Hot. And when the switch is on the "GND" reference point will float 17v (the internally provided Vs) below Line Hot.
In this case resistors will need to be rated for 170V (or 325V for 230V ac operation) plus any required safety allowances.
Does this sound reasonable ?