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Zero-crossing detector

2017-09-03 20:51  
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This zero-crossing detector uses a dual LM393 comparator, and easily controls hysteresis by the reference levels which are set on the comparator inputs. The circuit illustrated is powered by 10-V power supplies. The input signal can be an ac signal level up to 8 V. The output will be a positive going pulse of about 4*4 V at the zero-crossover point. These parameters are compatible with TTL logic levels. The input signal is simultaneously applied to the non-inverting input of comparator A and the inverting input of comparator B. The inverting input of comparator A has a 10 mV reference with respect to ground, while the non-inverting input of comparator has a -10 mV reference with respect to ground.
Zero-crossing detector

As the input signal swings positive (greater than 10 mV), the output of comparator `A` will be low while comparator `B` will have a high output. When the input signal swings negative (less than -10 mV), the reverse is true. The result of the combined outputs will be low in either case. On the other hand, when the input signal is between the threshold points (?±10 mV around zero crossover), the output of both comparators will be high. If more hysteresis is needed, the ?± 10 mV window may be made wider by increasing the reference voltages.



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