Dear Kai,

I am using zero cross detector for mains zero cross detection. Some products use LM311 comparator where as others use LPC922 internal comparator. Some time back you had suggested this circuit for my LPC922 internal comparators. I remember the red led you had suggested to prevent charge injection from transformer. Now, I want to know is this red led required even with LM311 based comparators the component values are ditto same as you suggested for LPC922 only diffrence is with LM311 i am using +5V single supply where as LPC922 was 3V powered.

Thanks & Regards,
Prahlad Purohit