4N35

[leonel]

Hi...
If I have a 0.7V AC between pins 1 and 2 on 4N35 optocoupler does I have a 5V output pin 5?
What´s the best way using an optocoupler to detect a corrent zero crossing?
If I have diodes supporting 5A and put two diodes foward and reverse biased between pins 1 and 2 of 4N35 does it work?

 

[Russlk]

Forward voltage for the LED in the opto coupler is 1.2 volts, so no it wont work with 0.7 volt diodes. If you want to detect current zero crossings, use a current transformer. Put a reverse diode across the input to protect the LED.

 

[leonel]

4N35 - 0.7 Voltage drop

I don´t want to use a corrent transformer, I don´t have space in my board and it isn´t economical...
In the attachment we can see that it´s possible just using diodes to detect zero voltage and zero current crossing!
The diference it´s that I have a much higher current, the maximum is about 10A, so I have to use power diodes (BY359 support 10A) to the current. The zero voltage crossing works with 0.7V diodes (1N4007). The diodes BY359, using in the corrent, has a 1.1 dropping voltage but I reduce to 0.7V.
Do you think I´m wrong or what I have to do?
Help me... I´m a little confused.
Regards
Leonel Monteiro

 

[Russlk]

That circuit could work, but I would add another diode in series with D3 and D4 to insure that the LED turns on.

 

[leonel]

Voltage Drop

So the ideia is having a voltage drop between pins 1 and 2 more than 1.3V, that´s the led voltage!? That´s righ?
Thank´s.

 

[Russlk]

Right.