hELLO,
i HAVE DESIGN ZERO CROSS DETECTOR USING LM393P, BUT I AM UNABLE TO GET OUTPUT WITH 50% DUTY CYCLE. 10ms on and 10ms off.
Please find attached circuit and wave from.
Please guide me.
With Regards,
Kavindra Gadhavi
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Kavindra
Kai's suggestion is much safer. Are you able to consider his recommendation?
Chuck
Hello Kai,
The signal 230Vac 50 Hz. is isolated by isolation transformer.
We face issue of comparator output level. it will not hold 5V for 10 mS.
Please guide us.
Kavindra
Hi Kavindra,
I would do it this way or similar:
This circuit prevents the input voltage from violating the common mode input voltage range and the absolute maximum ratings.
Kai
Hi Kavindra,
Kai’s circuit is the “cleanest”, and the preferred method.
You can also use a “split clamped” divider as shown in section 2.9.2.1 in the LM393 Appnote (page 9)
https://www.ti.com/lit/an/snoaa35a/snoaa35a.pdf
I would recommend using the LM393B, just because it has more robust inputs. This circuit also has the advantage that the inputs may be AC coupled with a (line rated safety) capacitor if isolation is needed. In your case, you would duplicate the divider on each input as you are doing a differential input.
Of course, the value of R1A needs to change depending on your application. D1 can also be a Zener to clamp the positive voltage.
There has not been any new input on this post in a while, so it will be closed.
If you have additional questions, please feel free to reply or open a new post.
thanks
Chuck