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Topic: AC Light Dimming [success] (Read 24783 times) previous topic - next topic


As there was a question on the necessity of  exactly 45 k resistors (that has been answered already), I just want to make a general remark about the resistors  in a zero crossing circuit like this: Obviously you do not want to make them too small and burn out your optocoupler, but in a circuit like the one discussed here ( http://fleck.rullz.lv/acdimmer/ac_dimmer_220V_circuit.png ), The intention is too keep the optocoupler in saturation until the zero crossing. If one cooses the resistors too big, upon appraoching the zero crossing the voltage might already  have dropped  too much to maintain  enough current through the optocoupler to get a positive spike on the secundary site of the optocoupler circuit. Your interrupt therefore may be triggered a bit before the actual zerocrossing, which may screw up yr timing. In principle it is possible that if you want full power of yr lamp and you would switch it on before yr zerocrossing, thinking you have switched it on immediately after your zerocrossing, your lamp would in fact be immediately turned off again

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