High power LED circuit

[famosas]

Hi, can someone help me to build an led circuit? i wan to build a study light for my nephew birthday
1st of all i do not have electronic background. im just like to build something by myself.
im self learning on the internet/books. so i want to build an led driver that can light at least 4-5 power LED. i already build it b4 this but just using a linear converter. now i learn that it is not efficient. i try search then i found buck converter. then i design a buck converter circuit. this is what i design btw.

*replace the resistor with LED
then i dont know how to proceed

i read that led has max current. higher than that led will burn. but buck only regulate voltage right?
how do i make it constant current so that led dont burn? i wan to add resistor series to the led but then i read that it also not efficient, better use linear then.
i also wan to make the led dim. can i just adjust the pulse? will the led dim?
how about pwm? 555timer will be enough?

*sorry for my english thanks

 

[Harald Kapp]

A buck converter can be built to control acurrent, not boltage, too.

Here is a discrete circuit.

However, you ma be better off using an integrated LED driver (with buck converter). Google "buck current regulator" and go to one of the manufacturer's sites (e.g. onsemi, ti, st ...).