Gentlemen:
I have a circuit problem I've been unable to solve:
I am using a switching power supply circuit to operate op amp circuits. I need an accurate zero cross detect of the incoming AC voltage from a "12VAC" wall transformer. In the attached circuit, if I use the voltage at "ACX" or "ACY", I see a distorted, clipped half-wave 'sine'. I tried an Opto-isolator across ACX and ACY, but it is too slow for an accurate zero cross. (I'm using a LM339 for the zero cross detect.) The only thing so far that works is to use a half-wave rectiifier (one diode) instead of the full-wave bridge. Then ACX shows a full sine when referenced to ground. (The LM339 needs the minus input grounded in single-supply mode.) How could I get some "isolated" sine referenced to system ground but still use a full-wave bridge?
Did I describe the situation well enough?
Thank you for any advice.
I have a circuit problem I've been unable to solve:
I am using a switching power supply circuit to operate op amp circuits. I need an accurate zero cross detect of the incoming AC voltage from a "12VAC" wall transformer. In the attached circuit, if I use the voltage at "ACX" or "ACY", I see a distorted, clipped half-wave 'sine'. I tried an Opto-isolator across ACX and ACY, but it is too slow for an accurate zero cross. (I'm using a LM339 for the zero cross detect.) The only thing so far that works is to use a half-wave rectiifier (one diode) instead of the full-wave bridge. Then ACX shows a full sine when referenced to ground. (The LM339 needs the minus input grounded in single-supply mode.) How could I get some "isolated" sine referenced to system ground but still use a full-wave bridge?
Did I describe the situation well enough?
Thank you for any advice.
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