I need help modifying the circuit below.
The assumption in this circuit as it stands is that AC Hot would be common to GND and then MT2 of the triac would go through a light source to AC Neutral. P_IRPT pulses high when there is no current flowing between MT1 and MT2 of the triac T1, which occurs at every zero crossing
The modification I need is for my case where AC_HOT is common to the 5V rail rather than GND (my power supply has a negative output).
I know there are other ways to detect zero crossing but this circuit gives the me assurance that I am definitely detecting the zero cross after it has occured so I never run the risk of firing the triac prematurely.
This was taken from page 16 of this TI app note: http://www.ti.com/lit/an/slaa043a/slaa043a.pdf