scr trigger??

Urgent (for a project):
How to trigger an scr at a specific angle and without any manual intervention?(i.e. we just need to use some variable component and the angle would change accordingly)...is it possible to use 555 timer in monostable mode and generate a trigger??...is it possible to change the firing angle if i use 555??..pls reply soon...i m planning to make a full wave bridge rectifier using scrs...pls give a ckt diagram for the trigger ckt if possible...also once i trigger the scr, will get completely off in the negative half cycle of the supply voltage?...the attached figure is the ckt diagram of what i m planning to make..

Hi Bulla,

Why you want to control four scr's is a complete mystery to me.
If you replace S3 and S4 with diodes you will get the same result
and you will only have to control two scr's.
You can expect "some" help from us but we won't do all the work
for you. However there's a schematic of a scr controlled power
supply here:

https://www.electro-tech-online.com/threads/voltage-regulator-using-scr.34612/

on1aag.

If you want to control four scr's, you can use the linked schematic, but you need to make a small modification.
A synchronisation circuit is required.
See the proposal in the attached image and try to imagine a circuit instead of "SYNC" black box.

**broken link removed**