Drawing current from the cell phone charger

[Yasserbn]

The output of the cell phone charger is 5v/ 850mA while the output of the USB port is 5v/ 500mA.
As you may know, we can charge our cell phones by plugging them either to the USB port (from PC) or to the charger that comes with it.

It means we can charge the cell phone even if the output current is less than 850mA because we charge it through USB which has no more than 500mA.

As a result. I am building a circuit that requires 5V/ 100mA, it is straightforward that I can draw this current from the cell phone charger. So it would be 100mA for my circuit and the remaining 750mA for charging the cell phone.

Is there any wrong if I do that? share me your idea.

 

[MikeMl]

You want to steal 100mA while charging the cell phone? Should work fine; it'll just take a little longer to charge...

Check the charger output under load with an O'scope to see how well filtered the DC is. You might be surprised to find some ripple there; the cell phone battery doesn't care, but your circuit might...

 

[audioguru]

The charger circuit in the cell phone does not take all 850mA from the 5V/850mA power supply. It might take only 200mA.

 

[Yasserbn]

. It might take only 200mA.

If the charger circuit takes only 200mA. What is the difference between charging the mobile phone from the wall charger and from the USB port?

Why MikiMI thinks that charging take a little longer time if I steal 100mA from the adaptor?