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<blockquote data-quote="DrakeJest" data-source="post: 739935">I have a optocoupler <a href="https://www.tme.eu/Document/9db3eeca23de5889dc2d7726469e9c88/PS817.pdf">PS817</a> that i plan to use for a zero-crossing detection circuit for mains 230V AC.<a href="https://i.sstatic.net/XWFOt9dc.png"><img src="https://i.sstatic.net/XWFOt9dc.png" alt="enter image description here" class="fr-fic fr-dii fr-draggable " style="" /></a>But i do not know how to size the resistance of R1 and R2 mainly because: I do not know what is the optimal value of the current that the LED of the optocoupler needs to be. Which value is it at the datasheet i should use (I mean it should be there right?). The absolute maximum is 50mA, so atleast that narrows it down. Im leaning on using 20mA but that number is just pure instinct and not really based on anything.Another problem which complicates things for me is, the resistor is placed before the full-bridge rectifier. I would assume its placed there over the DC side is for safety(?) as it immediatly limits the current of anything downstream. In this scenario how would the resistance be calculated (and power rating) of the resistor. The bridge rectifier part number is : <a href="https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/3738/KBL6080000L680.pdf">KBL608</a></blockquote>

[QUOTE="DrakeJest, post: 739935"] I have a optocoupler [URL='https://www.tme.eu/Document/9db3eeca23de5889dc2d7726469e9c88/PS817.pdf']PS817[/URL] that i plan to use for a zero-crossing detection circuit for mains 230V AC. [URL='https://i.sstatic.net/XWFOt9dc.png'][IMG alt="enter image description here"]https://i.sstatic.net/XWFOt9dc.png[/IMG][/URL] But i do not know how to size the resistance of R1 and R2 mainly because: I do not know what is the optimal value of the current that the LED of the optocoupler needs to be. Which value is it at the datasheet i should use (I mean it should be there right?). The absolute maximum is 50mA, so atleast that narrows it down. Im leaning on using 20mA but that number is just pure instinct and not really based on anything. Another problem which complicates things for me is, the resistor is placed before the full-bridge rectifier. I would assume its placed there over the DC side is for safety(?) as it immediatly limits the current of anything downstream. In this scenario how would the resistance be calculated (and power rating) of the resistor. The bridge rectifier part number is : [URL='https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/3738/KBL6080000L680.pdf']KBL608[/URL] [/QUOTE]

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