Zero Crossing Detector using IC 311
How to make a Zero Crossing Detector using 311 Op-Amp IC ?
A zero-crossing detector using IC 311 (8 pin DIP unit) is illustrated in figure. The positive (above 0 V) going input signal drives the output transistor on, the output going low (- 10 V in this connection). The negative (below 0 V) going input drives the output transistor off, the output going high (+ 10 V in this connection).
The output is thus an indication of whether the input is above or below 0 V. When the input is any positive voltage (above 0 V), the output is low level, while any negative input voltage will result in the output going to a high-voltage level.