USB and wall adapter power

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USB and wall adapter power

Although the STBC08 allows charging from a USB port, a wall adapter can also be used to

charge Li-Ion batteries.

Figure 5 shows an example of how to combine wall adapter and USB power inputs. A

P-channel MOSFET is used to prevent back conducting into the USB port when a wall

adapter is present and Schottky diode is used to prevent USB power loss through the 1k

Ω

pull-down resistor. Typically, a wall adapter can supply significantly more current than the

500mA-limited USB port. Therefore, an N-channel MOSFET and an extra program resistor

are used to increase the charge current to 850mA when the wall adapter is present.

Figure 5.

Combining wall adapter and USB power