How to monitor AC voltage with an optocoupler

[jmolivieri]

Key ideas

• Optocoupler with 2 LEDs => faster trigger
• Darlington topology => less power waste in the resistor in series with LEDs
  • Sink a current greater than dark current => Stability over temperature
  • Digital output => processed by an MCU => cheaper than making an hardware trigger.
    • Uses few resources of MCU

I propose a simple but tricky schematic to monitor mains. I got inspired by this post. I changed it a bit for my requirements.

Key points

• Temperature range : -20°C to 85°C
  
• Input signal : 210 to 230V RMS, f : 50 to 60Hz
  • Lowest input : 200V RMS
• Output signal is a digital LVTTL (VCC=3.3V)
  
• Output signal frequency is twice the incoming signal : mains
• FOut : 100 to 120Hz
• Low power on the input stage : 160mW

This circuit is very simple to assemble. But I simulatied over temperature range : -20°C to 100°C for

• Optimum operating conditions
• Minimum operating conditions
• Leakage current

Notes

• IE in simulation is negative : it's just to say it comes out of the optocoupler.
• To get its extrememum I had to evaluate : min(I(U1:e)) : the most negative value.

To use it, one just has to measure time between 2 positive or negative edges : a bit like a watchdog : if you don't receive an edge within 15ms for instance, it means that input is off.

Please note I'm french. In my word processing "." were changed with ",".
If I wrote something wrong or inaccurate please tell me.