Trying to Understand Interacting Components...

[mriksman]

I have the following circuit on a board.



If I leave DIM2 floating, then when I ground DIM1 - it only dims from 240VAC down to 151VAC.

If I ground DIM2, then when I ground DIM1, it will dim down fully to off.

How is DIM2 pin affecting DIM1...?

[mriksman]

I have some more observations

With DIM CONTROL2 floating, and DIM CONTROL 1 grounded, GATE1 voltage is 0 and GATE2 voltage is 16.6V (which is fully ON; internally the IC has a 17V driver).Which is to be expected. If DIM CONTROL1 = 0V, duty cycle is 0% so the RMS of the GATE1 voltage is 0V. Additionally, DIM CONTROL 2 is actually C3 charged to 5V (internally Vdd of the IC generates 5V). 2.5V is 100%, and anything over 4V is actually a special case to let the IC know to turn off switching and go full ON. As such, the GATE2 has RMS voltage of ~17V.

Yet I am seeing LIGHT1 partially ON (154V)!? Yet GATE1 is OFF. Somehow it's being partially lit from the GATE2/LIGHT2 MOSFET