zero crossing detector

79 zero-crossing detector There is nothing very special about a zero-crossing detector. However, this particular circuit has an unusual feature. A certain signal level must be present at the input of the circuit before the signal at the detector results in an output signal. This therefore makes it possible for the circuit to ignore interfering signals at the input (such as noise and low- amplitude mains pickup). Potentiometer Pl is used to set the sensitivity of the detector. The trigger threshold of the circuit is 300 mVp when Pl is fully rotated. Opamp Al is configured as a voltage follower. The signal is then applied to two O.M. Kellogg 15V® o C2 10y 25V C1 4 1O 25V Schmitt triggers whose hysteresis is determined by the ratio of resistors R9 : R4 and R8 : R7. Opamp A2 detects the zero-crossing of the rising input voltage. Preset poten- tiometer P2 is adjusted so that the lci elektorjuly/august 1983 u CpI_lt J 1 (-15 V) to logic 1 (+15 V) precisely at the instant of zero-crossi...