looking for help with some basic circuits

[mike134]

Hey guys
I am just beginning to learn how to build circuits that don't fry themselves and just want someone to tell me yeah that should work or smack me and say u idiot. anyway is there anything wrong with charging a usb device with a 9 volt battery and something like a 7805 voltage stabilizer. the downfall i can see to this is I don't believe it be very efficient. the other one is real easy do i need anything between a 12 volt power source and a 12 volt fan.
thanks for any help
Mike

 

[farhada]

The answer to the first questions is no, it is OK, but you have to be careful since some devices may get damaged if the USB has too much current.

he second answer is no, you can connect it directly without any problems.

 

[mike134]

sorry i also forgot to add in the first one were would i add a LED on light and a switch does it matter. and also is there something else i should include in the charger ciruit

 

[withoutego]

A related question. I recently bought a Euro style plug charger (USB) for a friend in Madrid. I checked it (it is universal as to input AC) and its unloaded output was 11 or 12VDC. Does the USB standard allow this? if so how much is too much for a USB device. My friend was recharging her cell phone with her laptop, this will be easier. Thanks

 

[farhada]

This is kind of normal since most of these cheap devices regulate the voltage only if there is a load connected to it. The best way to test these units is to connect a small 6V lamp to it and then see see the voltage over the lamp.