I have generated a square pulse of width varying with input voltage by passing a square wave output of comparator through a diode. This will be used to trigger a thyristor. But I need another square pulse 180 degree firing angle apart from the one already generated to trigger another thyristor. How would I do it using 555timer? Are there any other delay circuits which would serve the purpose? Please explain.

 

Use a transformer with a 9-0-9 volts ac winding.
Use one diode in each of the '9'volts tap.
You will get two separate half waves 180 deg apart.
Use a 1 K resistor and a 5.6 volts zener after each diode.
The wave form becomes two square waves 180 deg apart.
The higher the secondary voltage, the more linear the square wave shape.
Use these signals along with the 555 output and your nand logic to trigger the thyristors.
regards,
Maanga

 

Hello shiboo - if you show some schematics of your system then it would be easier to offer suggestions. I'm guessing maanga's suggestions are based on an assumption that this has to do with a mains frequency based thyristor firing control - but whether that is the case isn't clear from your original post.