Introduction:
Zero crossing detectors are electronic circuits used to detect the zero crossing points of a signal. They are widely used in various applications such as power control, frequency measurement, and waveform generation. However, zero crossing detectors have a drawback that can be overcome by using positive feedback.

Drawback of Zero Crossing Detectors:
The main drawback of zero crossing detectors is their sensitivity to noise and fluctuations in the input signal. In the absence of noise, a zero crossing detector can accurately detect the zero crossing points of the input signal. However, when noise is present, it can cause false triggering and inaccurate detection of zero crossings.

Explanation:
Positive Feedback:
Positive feedback is a technique used in electronic circuits to enhance the desired characteristics of a system. In the context of zero crossing detectors, positive feedback can be used to overcome the drawback of sensitivity to noise.

When positive feedback is applied to a zero crossing detector, it increases the gain of the circuit near the zero crossing points of the input signal. This increased gain helps to amplify the signal while suppressing the noise, thereby improving the accuracy of zero crossing detection.

Working:
The addition of positive feedback to a zero crossing detector can be achieved by connecting a feedback resistor from the output to the input of the operational amplifier or comparator used in the circuit. This feedback resistor creates a feedback loop that amplifies the signal near the zero crossing points.

When the input signal crosses the zero point, the output of the comparator or operational amplifier changes state. This change in output state is fed back to the input through the feedback resistor, resulting in an amplified signal near the zero crossing point. This amplified signal is less susceptible to noise and fluctuations, making the zero crossing detection more accurate.

Advantages:
The use of positive feedback in zero crossing detectors offers several advantages:
1. Improved accuracy: The enhanced gain near the zero crossing points improves the accuracy of zero crossing detection, even in the presence of noise.
2. Noise suppression: The positive feedback helps to suppress noise and fluctuations, reducing false triggering and improving the overall performance of the circuit.
3. Increased sensitivity: The amplified signal near the zero crossing points increases the sensitivity of the zero crossing detector, allowing it to detect smaller changes in the input signal.

Conclusion:
In conclusion, the drawback of zero crossing detectors can be overcome by using positive feedback. This technique increases the gain near the zero crossing points, improving the accuracy of zero crossing detection and suppressing noise. The use of positive feedback enhances the performance of zero crossing detectors in various applications, making them more reliable and efficient.