Zero Crossing Detector (ZCD) | Comparator Circuit Using 741 Op Amp

A zero-crossing detector(ZCD) is a voltage comparator that switches the output between +Vsat and –Vsat (Vsat: Saturation voltage almost equal to 14V) when the input crosses zero reference voltage. Then what is a comparator? In simple words, comparators are basic operational amplifier circuits that compare two voltages simultaneously and switch the output according to the comparison. We can say the zero-crossing detection circuit is a comparator example. We will discuss in detail about comparator in our upcoming articles. Inverting zero cross detector circuit schematic using op-amp 741 IC is shown below along with working, input-output waveforms.

Zero Crossing Detector (ZCD) Circuit Diagram

Components Required

1. Op-amp
2. Power supplies
3. Function generator

ZCD Input and Output Waveform

Working principle of Zero Crossing Detector Circuit

• The working of ZCD can be easily understood if you know the working of a basic opamp comparator.
• In ZCD, we are setting one of the inputs as zero i.e. zero reference voltage.
• The output is driven into –Vsat when the input signal passes from zero to a positive direction.
• Conversely, when the input signal passes from zero to a negative direction, the output switches to +Vsat.

Conclusion

ZCD is a basic op-amp circuit that can be used to check whether the op-amp is in good condition. Zero crossing detectors can be used as frequency counters and for switching purposes in power electronics circuits.