Zero cross detector, 230V cheap and small

[Jadeit]

I need to detect the passage of the mains voltage to zero due to the power control using the MCU .
I am looking for a reliable, cheap and small ZCD .
I would like to use AC Optocupler PC814 with two small 1k SMD resitro 1206 + two SMD 100nF X7R 500V 1206 capacitor.

Power consumption ia only 35mW.
Yes, the endurance is only 1000V, but when you put it on, there is an insulating barrier for the optocoupler.

Do you consider this a good idea?

 

[FvM]

A problem of your design is that it creates near to 90 degree phase shift, thus not actually signalling zero crossing.

 

[Easy peasy]

FvM is correct - the current leads the volts by quite a few degrees ( more than 80 deg in fact ) in the circuit you propose - also you do not need two caps in series - unless for safety reasons if each was 275Vac rated.

Better to have resistors, 10mA pk = 33k approx, = 4 x 8k2 approx, each 200V rated, each 1W rated, dissipating 410mW,

this will give you zero current in the otpo at the mains voltage zero crossing ....! ta da ...! and pin 4 will go high briefly ...

 

[KlausST]

Hi,

Why not doing a forum search, or an internet search, or reading IC manufaturer's application notes?
There are so many proven circuits. Many of them come with descriptions and calculations.

Klaus

 

[Jadeit]

Yes there is a capacitor, yes he rotates the voltage / current, but that does not mean that the result is rotated by 90 st and the ZCD will detect a voltage peak

Her is simulation on my design
Red is voltage 230V
Green output of optocoupler
Yellow is current over LED in OC
Blue current over second LED in OC
The circuit detects a zero of about 1500 us over a true zero

Her is same only with 2x 35k resistor
The circuit detects zero about 1500 us after true zero
Yes both for LED current 5mA
Consumption circuits approx. 750mW against 35mW with C + R

Her is precise and complicated ZCD
Detection exceeds zero by about 500us
Consumption about 180mW ,but 13 components , in longlife and SMD 15 becouse R1 and R2 it is advisable to always replace the pair 1206 4x 110k (voltage stress)

Do I see something wrong?

 

[FvM]

You didn't mention what's the purpose of ZCD in your application. If it's something like phase angle control relative to actual voltage zero crossing, both circuits are usuitable due to badly defined phase relation. If it's just frequency counting - no problem.