Dear Kai,

Thanks a lot for your reply and the schematic. I still have some doubts. As far as I understand... [ Please correct me If I am wrong ].

1. On the non inverting terminal you choose 20k + 1k and 10k to establish a voltage refrence of 1.33V National App notes use 100k and 10k with 15V and extablish 1.36V [Same] reference voltage.

2. On the inverting terminal you use 1N6263 to protect the Comparator input from over and under voltages. The first 1N6263 i.e. in parrallel with Red LED protects from undervoltages. During negatve half cycles on input signal the 1N6263 conducts and protects. During this period the voltae at Kathode of this 1N6263 is -700mV to protect Comparator from this negative voltage you use 20k and 5k1 at inverting terminal. The voltage between Vcc and Kathode of this 1N6263 3V - ( -0.7V ) = 3.7V The Voltage at Inverting terminal with respect to 1N6263 Kathode = (3.7/(20+5.1))*5.1=0.750 Volts Thus the inverting terminal is safe at approx. 0V during negative half cycle of input.

3. Finally to balance the 10k at non inverting terminal you use two 5k1.

The Doubts now I have are...

1. What exactly is the function of Red Led? Are there any requried specifications for this LED or any red color led will work?
2. I read 1N4148 and 1N914 datasheets and these datasheets mention the Reverse Leakage current in nA. & I can't see any significant diffrence between 1N6263 and 1N914/1N4148?
3. It appears I will need a pull up reistor at comparator Output what care is to be taken for this pull up value.
4. Can I apply signal on Non - Inverting terminal and Reference on Inverting terminal. And the values can be kept same?

Thanks & Regards,
Prahlad Purohit