whats a BP2834B chip?

[liquidmagma]

i got the chip from a led light bulb.

[mariushm]

Probably a not isolated buck led driver IC, similar to this one below (BP2831)

 

later edit: nevermind, found it on the website (well, the one with A at the end, not the B version.. the b version is probably b-grade, or lacks some protection circuits inside) : http://www.bpsemi.com/product/bp2831a.asp

 

You can try to find the information about your chip at the manufacturer (BP Semi) : http://www.bpsemi.com/

BP2831-BPS.pdf