Zero Crossing Detector

Zero Crossing Detector using 741 IC

How to make a Zero Crossing Detector using 741 IC ?

Zero-crossing detector is an applied form of comparator. Either of the op-amp basic comparator circuits discussed can be employed as the zero-crossing detector provided the reference voltage V_ref is made zero. Zero-crossing detector using inverting op-amp comparator is depicted in figure. The output voltage waveform shown in figure indicates when and in what direction an input signal v_in crosses zero volt. In some applications the input signal may be low frequency one (i.e. input may be a slowly changing waveform). In such a case output voltage v_OUT may not switch quickly from one saturation state to the other. Because of the noise at the input terminals of the op-amp, there may be fluctuation in output voltage between two saturation states (+ V_sat and – V_sat voltages). Thus zero crossings may be detected for noise voltages as well as input signal v_in. Both of these problems can be overcome, if we use regenerative or positive feeding causing the output voltage v_out to change faster and eliminating the false output transitions that may be caused due to noise at the input of the op-amp.