Dear sir,
I am looking for power supply for end application. Initially used transformer based design for end application.
now i am planning to use transformer-less power supply. I have 3 phase R,y,B . In this 3 phase i would like to use 1 phase for 12V generation
output required 5V 0.5A
my question is is it safe ?? what care to be taken .
Regulator IC
https://www.mouser.in/Datasheets/_/?Keyword=L78M05&FS=True
My question is is it safe ??
No, it's bloody lethal!
What care to be taken.
Don't build it!
It bothers me that you are even asking. If you are proposing to work with 3 phase but cannot see that your proposed circuit is dangerous that suggests to me that you don't have enough knowledge to work with mains.
Buy a ready made power supply, someone else will have done the hard work making a safe design.
Also, don't use a linear regulator, they just waste power.
no, that is an entirely inappropriate solution.
If you need 5v, why are you messing with 12v? Just use a phone charger - dirt cheap, readily available, and the manufacturer has already done the work of making it safe and designing an efficient switch mode power supply.
This is 2020 - switch mode power supplies are dirt cheap, highly efficient, and readily available. There is no need to be halfassing it like you are proposing.
Note that I do not oppose using linear regulators under all (or even most) circumstances - they are cheap, and if power efficiency isn't a big priority (which it often isn't), and trivial to wire up - just add two caps and you're done. If you already have a DC voltage a bit higher than you need, and the current is low, I use linear regs all the time. But if you're starting from AC, just use an off the shelf power supply! That said, the 7805/78M05 are trashcan regulators; your go-to regs should be 1117-series (LDL1117 is my go-to now - I used to do ZLDO1117s, but both quiescent current and dropout are better on the LDL1117)
Hi,
What is wrong with the transformer solution?
Tom.... 
AJITnayak,
I suggest you do what I do; I collect power supplies from old electronics that's being thrown away. I have a ridiculous number of them. Most I will never use, but I can usually find a power supply for just about anything.
TomGeorge:
What is wrong with the transformer solution?
Equally unsafe.
OP already has a voltage divider connected to 3-phase, with neutral directly grounded to the Arduino.
Leo..
OP's image.
I didn't notice when I first replied, putting the Voltage monitor circuit alongside the proposed power supply won't work anyway as there will be a short on the bridge rectifier in the proposed power supply.
If you want to monitor mains like that I suggest you need to build your monitoring system in a self contained, sealed, earthed, inaccessible box. Power it with its own power supply not used for anything else and use serial for the output through an opto-coupler capable of carrying data. There should be an isolation barrier between the mains side and the safe side of the opto-coupler, either a slot in the PCB or an earth track on both sided of the PCB running between the pins, with the earth track connected to mains earth.
Hi,
What is the application?
Does the timer control anything?
Tom....
Another "if you are asking here, you probably are years off the necessary training, skills and experience for this project"! 
Yes i would like to control Relay when voltage below set level.
Voltage transducer with 0-5V output will be expensive solution
if i use transformer in each phase like example shown in arduino my electronic became more.
I have seen some design where they use high wattage voltage divider networks.
If safety is concern i would like to know safer design for this application.
since i am driving 12V/24Vdc relay i prefer 12V/24V power supply. power consumption will not exceed 0.5A @12V/5V when converted.
Is there any recommended Phase monitoring solution in electronics.
AJITnayak:
If safety is concern i would like to know safer design for this application.
The problem isn't just the circuit design. Without wishing to be unkind or rude, if you have to ask these questions you don't know enough to construct any circuit like this safely. It doesn't matter how good the design is if you don't know how to assemble it to be safe. Safety isn't just in the circuit design.
The problem with us helping you is that while we can give advice we can't supervise you, and we can't supervise anyone else who reads this and uses the information. If I knew you personally and you were asking me about this and you could work at my bench under my supervision then I'd help you build your project, but that's not possible.
With respect, I am concerned you are out of your depth and don't know what mistakes might kill you.
AJITnayak:
Voltage transducer with 0-5V output will be expensive solutionif i use transformer in each phase like example shown in arduino my electronic became more.
What is your Neutral to Phase voltage?
If you use a transformer on each phase it will be safer and provide 0 to 5V output.
A little extra construction will probably mean the further away you are from electrocution and fire.
If your controller has any contact with the outside world, like through a potentiometer shaft of any part of your project being to close to a grounded item you need to consider this.
If you want to be "cheap" understand the consequences.
Tom...