I have FIIO E3 headphones amplifier which is powered by 1.5V AAA battery. Am I using it just with my PC, so I got an idea: why don't I power it using USB port and stop buying new batteries ?
Anyway, I have few questions regarding that:
1) I know that USB port can give 500mA, but somewhere I've read that you can get only 100mA without enumeration. Is that true ?
2) Will 100mA be enough for replacing 1.5V AAA battery ? What is the maximum current that 1.5V AAA battery can give ?
3) Let's say that 100mA is enough. Now I need to build something :) I've thought about using LM317T. In it's datasheet, there's a foruma like this: Vout = 1.25V*(1+R2/R1)+Iajd(R2). If I'm reading the datasheet correctly, Iadj will be really small, so I don't have to worry about that. R1 is fixed at 240 ohms. So I only need to worry about R2. After calculating, it should be around 50 ohms. Or did I do something wrong ?
4) If I get 100mA @ 5V, is it true that I can get about 300mA @ 1.5V ? I don't know why this could be right or not, so I'm sorry if I've said something really stupid :)
Thanks for your help !!!!