# HCPL3700 - 220V sensing circuit

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

• R29 is unlikely to have a voltage rating of the peak of your mains voltage, $220 \sqrt 2$. It should be made up of two or more series resistors. – Transistor Apr 22 at 15:41
• C30 will not work. When in pull-up it will charge the 10uF cap slowly via R28, a 10k resistor. When in pull down it will pull down almost instantaneously, shorting any voltage on the capacitor. Destructive. I think you need a 100k series resistor before C30 to fix both problems. – scorpdaddy Apr 22 at 18:06