Re: supply voltage
yassin.kraouch,
You could use a linear regulator, such as the LM317, with an external pass transistor. See the app notes for the LM317 at **broken link removed**.
However, keep in mind the power (23.4 Watts) that the pass transistor must dissipate. You would need a fairly large heat sink to keep the chip temperature of the pass transistor less than 150 deg C. A more efficient solution would be a buck switching regulator. You can find lots of reference designs for this type regulator on the web.
Regards,
Kral