High voltage (220V) constant current LED driver using transistors
But i'm wondering is it possible to connect it to 220v mains voltage (311V DC after using bridge rectifier) if i used a proper high voltage transistors such as A42 or 13001 instead of low voltage BJT?


It's possible. It'll even work. Whether it's safe or not is something that'll be hard to answer.

It's also not very necessary: grid voltage is pretty reliable, so a simple series resistor would do just as well in practice (and also, would not tend to fail short as much as a transistor does, so it'd probably be safer).

Another problem is thermal stability. When the temperature of this rises, so will the current amplification of the transistors, and thus, you're building a recipe for thermal runaway and self-destruction.


  If yes so why i never seen before commercial LED driver that used this simple method?


When you have 100 LEDs in series, there will be differences in brightness among them. Little use having perfect current regulation.

Also, that's a 30W LED light. That is wall painter's floodlight bright. That's not something I would expect you to take apart on a daily basis.

Therefore: For places your simple regulator would work, a resistor would do as well, and be cheaper, and safer.


  If yes so why i never seen before commercial LED driver that used this simple method?


Also, because this is almost never a useful thing to do:

Think about it: the voltage that has to drop over this regulator (and potential series resistors you'd add) would always be your DC voltage minus your LED string voltage.

In your use case, you can make that drop tolerably small (11V), so that the power wasted here is tolerably small (4% of the LEDs' power). This thing is still going to get pretty hot.

When does that actually ever happen? White LEDs, due to the physics behind how they work, always have a forward voltage of around 2.8 to 3 V. So, to achieve a drop that's as tolerably low as yours, you'd need to put 100 LEDs in series.

Nobody in their right mind would produce a lamp like that! 100 LEDs in series means that your whole lamp is broken when 1 or more out of 100 LEDs is broken. 


Say, each of your LEDs have a probability of being broken of 1 in 10,000, 10⁻⁴.
So, the probability of an LED being OK is 1-10⁴= 0.9999.
So, the probability of 100 LEDs in a string being OK is 0.9999¹⁰⁰, that's 99%
1% of your lamps are broken
Since 1% is so much that the companies selling these lamps to customers will not stock your lamps, because they will have to deal with customer complaints and their image will suffer, you now have to test every single lamp before you ship a pallet of them. That increases the cost of your low-cost lamp by a significant factor.


Yes, that would require a switch-mode power supply. As said by others, that is often necessary, anyway, for isolation requirement reasons.