ericgibbs

Hi,
Checking thru the LM393 datasheet, there is an application circuit that meets your requirement.
See attached extract from the LM393 datasheet.

Its a zero crossing detector, feed the 6Vac from the mains isolating transformer into the Vin input
and connect the XOR gate input to the LM393 output.
Use a single +5V supply for the LM393 and XOR logic.

If you cannot simulate a LM393, try any single supply comparator that you have in the sim,,, or even a good quality OPA.

Lets know how the sim goes.

Attached Images

ZeroCross1.png (42.9 KB, 10 views)

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Eric
"Good enough is Perfect"

PIC tutorials:
Nigel's: www.winpicprog.co.uk/
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

mrrmot

Hey ericgibbs,

I've done the simulation with op-s, and everything works fine. I wanted to use a comparator because I thought they are more precise.

Thanks a lot for the above circuit. One more question: Which is the max voltage that I can connect to the Vin input of LM393 in the above circuit? Do I have to change anything in the scheme if the amplitude of the sines is 5V, 12V or 15V?

Thanks for everything

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Dazed&Confused

ericgibbs

hi,
The diode clamps that range of negative input voltage half cycles, it has a 5K1 resistor in series with the diode so the current is also limited to a safe level.
If you are concerned about the higher positive half cycles, you could replace the diode with say a 3.9V zener.

Do you follow that.?

EDIT: added dwg

Attached Images

ZeroCross2.png (42.3 KB, 7 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Nigel's: www.winpicprog.co.uk/
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

mrrmot

Yeah, thanks, I think this should work well, now I can finish my scheme. I'll let you know whether my teacher approved it.

Thanks

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Dazed&Confused