Thread: Modification: Charge via USB
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Kybo_Ren is offline Kybo_Ren
2007-07-04 , 09:46
Posts: 20 | Thanked: 0 times | Joined on Jul 2007
#35
Originally Posted by Jeffus View Post
I agree about not using power from the 770 to get the USB host mode working, as you can't internally limit the amount of current your devices will pull.
Sure you can!
It just requires a little ingenuity and a trip to DigiKey
If you use a JFET and a resistor (or even better, two resistors that can be connected and disconnected via a switch) you could regulate the output current.

USB spec is 500mA MAX for USB devices. You typically only see this with long strings of devices or really really power-hungry devices. Most peripherals wouldn't need the full 500mA (hence the switch for two current ratings).
Since the charger is rated for 900 mA (apparently), the battery can handle at least that much current. When you figure the OMAP 1710 with its main core and DSP running at full speed probably around 200mA, wireless transmitting at full 20 - 30mA (100mW max), etc., your max current usage is probably around 400 or 500 mA, so even an extra 500 mA won't kill it.