EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Freshman on September 26, 2024, 05:59:06 am
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I have a question.
Can I use this part (https://ww1.microchip.com/downloads/aemDocuments/documents/MSLD/ProductDocuments/DataSheets/MIC6270-IttyBitty-Comparator-DS20006294A.pdf (https://ww1.microchip.com/downloads/aemDocuments/documents/MSLD/ProductDocuments/DataSheets/MIC6270-IttyBitty-Comparator-DS20006294A.pdf)) in place of this part (https://www.ti.com/lit/ds/symlink/lmc7101.pdf?ts=1727329844036&ref_url=https%253A%252F%252Fwww.google.com%252F (https://www.ti.com/lit/ds/symlink/lmc7101.pdf?ts=1727329844036&ref_url=https%253A%252F%252Fwww.google.com%252F)).
The application is for ZCD where the input to the op-amp will be coming from an opto-isolator and given to the non-inverting terminal.
U21 in the attached image.
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The circuit has no high demands on the comparator.
The MIC6270 has an open collector output and would thus need an extra resistor to Vcc at the putput side (may be forther down the circuit).
The circuit has quite some filtering action and will thus have a delay and may not trigger at zero crossing, unless there is some oopsite phase shift at the drive side (e.g. capacitive dropper). Ideally one would like additional hysteresis (feedback to the + input) to avoid douple triggering from noise.
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Thank you for your answer @Kleinstein.
Would MIC6270 be sufficient for the application? If so, just adding a pull-up (any suggestion on the value?) at the output would be fine?
Could you share some schematic drawing circuit that you suggest for this circuit?
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I got confused with the use as ZCD (zero corssing detector) and thought of a comparator. The circuit as shown is using the OP-amp as a follower, not a comparator. For this use a compartor would not be the right choice. One would want a real OP-amp, something like an MCP6001 / MCP6006 / LMV321 or any low voltage (usually CMOS) slow OP-amp. It depends on the later use of the signal if one needs the buffer at all.
A ZCD could use a comparator too, but this would be a different circuit and it dempends on what is done with the signal.
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Whats the input to the opto from , what sort of frequency ? Is it more for just logic high/low, or is any of the signal meant to be in the linear region for the transistor ?