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I have a DC voltage source (between 5 and 10V) from which I want to charge cell phone with a USB cable. I believe that using a LM317 or similar IC for charging cell phones is not a good idea as most cell phones are coming with Lithium-ion batteries, which requires constant current phase first, then constant voltage phase. I have seen MAX1555 IC but it gives only 4.2 V as regulated output. If I connect a VBUS (usb cable) from MAX155 chip to iPhone, my iPhone may not charge because it's less than 5 V.
Can anyone give some insight?