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I'm having few issues with chargers, current delivered to a device etc... just need to connect the dots I guess.

When I connect a phone to a charger for example IPhone which is rated at (5v,1A max), to a charger rated at (5v/2A) The phone will only draw 1A correct? what is limiting the current here? is it a resistor in series built inside the phone?

If I'm Building a PowerSupply that has a charging USB port, do I need a resistor before it? or would it cause a short circuit? For example (Voltage source) ---> (LM317 as voltage source) ---> (USB Port) -----> (Phone) do i need a resistor before the USB port or will the phone handle it?

Also, charging a lipo, let us say 1cell at 4.2v maximum, if i set the LM317 to 4.2v and plug the lipo, am i forced to put a current limiting resistor or will the lipo draw as much as it needs as the voltage is appropriate? wouldn't the charger stops automatically when the voltage off the battery be equal to the voltage of the lipo? 4.2v ---- 4.2v so no current will flaw?

Long Question short, is the current limiting resistor built in the batteries or do I need to place one? wouldn’t the charging stops automatically due to Vin = V of battery?

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What Apple, Samsung, Motorola and other phone manufacturers call "charger" aren't actually chargers at all - they're power supplies. The actual charger circuit is embedded into the phone.

So as for your question as to what limits the current consumption of charging the battery - it's the battery charger. And it's much more complicated than a simple resistor. Especially for lithium chemistries. This is because lithium based batteries (lion, lipo, liFe) tend to overheat and burn/explode when charged or discharged too fast.

I strongly advise you not to try charging a bare lipo battery using a simple regulator such as the LM317. There are chips designed specifically for charging lithium batteries such as the MAX1555 that prevents the battery from overheating.

For charging a phone however, all you need is to supply the right voltage with enough current. Doable with the LM317.

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