USB charger circuit

> You have presented no compelling reasons for using a USB port.
> And there have been many responses suggesting that it's a bad idea.

The reason is that we have to provide some power source for the charging ho=
lder of a portable device, either attached or detached to the A/C plug.  If=
 we supply with attached plug, we have to worry about the A/C plug itself. =
 USB A/C plugs are widely available and cheap.  But because USB ports are a=
lso available on PC and laptop, we have to worry about them.

However, a properly built PC/laptop USB port should limit the current and/o=
r disable the noisy port.  USB devices would not have been so popular witho=
ut this simple and fundamental safe-guide.=20