Electronic – Zero Crossing Detector Circuit

diodespower electronicstransistorszero crossing

I am working on a zero crossing detector circuit. Can anyone please explain the function of highlighted circuit?

schematic diagram

Best Answer

Q1 and D5 act as a pair of anti-parallel diodes allowing current to flow both ways through C1

when C1 is charging the current flows through D1, when discharging through Q1s base to it emitter.

This discharging turns on Q1 lighting the LED

The claim that this is a precision zero crossing detector seems dubious.