Electronic – HCPL3700 – 220V sensing circuit

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I want to use HCPL3700 optocoupler for sensing 220V (line).
I design a circuit but I want to ask some questions.

  • HCPL3700 is an open-collector output so I pull-up Vout. In AC voltage sensing some people says HCPL3700 is halted on zero-cross so I add a cap (C30) is this (10uF) enough for zero-cross pulse filtering?

  • I add a resistor (R29) (100k) to the input of HCPL3700 for 200V threshold is this ok?

thanks

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Best Answer

Yes, not only is R29 OK, I think it might be mandatory. Take a look at the graph below from the data sheet. It indicates that the value of the series resistor affects the detector's switching threshold. It's hard to tell from the graph which curve to use. Suggest you use the 100K and then measure the voltage where the detector changes state. Tune the value of R29 until you're happy with the voltage threshold.

Fig. 8 External Threshold Characteristics graph from HCPL3700 datasheet

(Image source: Figure 8 from HCPL3700 datasheet)

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