I am looking for a way to power my MP3 player which takes a 1.5 battery every 12 hours. I use it most of the time while working in the computer. So I want to use a usb port to get 5v and lower the voltage by using a 1.5 zener diode (*). The problem is that I don't find such diode in the market. How can I regulate the voltage to 1.5? (*): 5-1.5=3.5v Mp3 draws about 100ma. 3.5/100ma = 35 hom resistor. Rpower= 3.5*100=0.35W, Use 1/2 watts ZdiodePower=1.5*100ma= .15w, Use 1/4 watts.