| ??? 12/04/05 02:37 Modified: 12/04/05 03:08 Read: times |
#104651 - Not at all ! Responding to: ???'s previous message |
Erik said:
17 or 20,mV is still waaaay too small a hysteresis.. that littele is "usual noise". Why are you telling this?? 20mV is not at all a too little hysteresis for a zero crossing detector! In order to hit the zero crossing correctly for both polarities, hysteresis should be as small as possible. I have successfully built zero crossing detectors with even much less hysteresis! Zero crossing detectors showing much larger hysteresis are useless, if the exact moment of zero crossing for both polarities is to be detected. 17/20mV will pick up if anyone in the neighborhood makes a "gaseous contribution" And it's the job of layouter to prevent that there's a noise source in close neighbourhood doing this. By the help of correct grounding and filtering such a zero crossing detector will work perfectly! By the way, the original circuit from National Semiconductors, which you will find here http://cache.national.com/ds/LM/LM139.pdf shows a hysteresis of even less than 7mV... Kai |
