Re: Looking for two-input comparator with hysteresis

Ken Smith wrote:
In article <44734782.2000200@xxxxxxxxxxxxxx>,
Christopher Tidy <cdt22NOSPAM@xxxxxxxxxxxxxx> wrote:

Hi all,

I'm building a digital clock circuit which will use the AC mains frequency for time keeping. I need a circuit (preferably a single IC) which can be connected via a transformer to the mains supply, and will send one output pulse to my TTL for each complete supply cycle. I think it would be good to include some hysteresis in case the AC mains waveform is noisy. I'm concerned about using a simple Schmitt trigger, where the input is taken relative to the lower power rail, in case I create a loop which causes a large current to flow back through the linear power supply. So I'm looking for a comparator with two high impedance inputs and hysteresis. Does such a thing exist as a single IC?


You may want to look at some of the low power comapritors from Linear.

You also can make an LM311 have hysteresis buy feeding back from the output to the offset trim. Check the data *** for an example circuit.

You can also do what you want by slightly abusing a quad op-amp such as the LM324. Three sections can be used ot make a classic dif-amp. The 4th section can have positive feedback so that it acts as a comparitor.

Thanks for the suggestions, Ken. I'll look into those ideas tomorrow.

Best wishes,

Chris

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