Optically Isolated Phase Controlling Circuit

[aratti]

For getting knowlege, can you please explain why zener diode (D5) and resistor (R2) is used in this circuit?

Detecting the zerocrossing correctly (without delay) is not a simple metter. Here we have got to thrust Fairchild engineers.

When you have got a working circuit, with the proper zerocrossing pulse detected by your oscilloscope, then tray to remove some components you judge useless and see the result on your scope. If pattern doesn't change you were right otherwise you will have to resolder the component in its original position.

This is the best way to learn.

And also please tell me, if I want trigger upto twenty five LM555 for controlling upto 25 fan, which transistor I need to use instead of MPSA40. Is this transistor has enough current to trigger upto 25 LM555?

I don't recommend to use this solution having a long wire connected to pin 2 of LM555 will works as an antenna with unpredictable results.

You should have 25 complete circuits, you can supply the 12 Vac directly to all 25.



Al

[dhanush]

Detecting the zerocrossing correctly (without delay) is not a simple metter. Here we have got to thrust Fairchild engineers.

When you have got a working circuit, with the proper zerocrossing pulse detected by your oscilloscope, then tray to remove some components you judge useless and see the result on your scope. If pattern doesn't change you were right otherwise you will have to resolder the component in its original position.

This is the best way to learn.

Al

I am not trusting EFY Magazine schemetic that why I am using Fairchild schemetic. EFY Mag is Indian edition. I am developing this project is for business purpose, so I need quality product. Good reply and thanks.