You can't charge your iphone with your ipad charger.
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There's a reason Apple has different chargers for the ipad and iphone. Because the battery capacity of the iphone is small, only 1A current is required to complete the charge. Although a larger charging current can charge quickly, it is more likely to cause the phone to heat up, and high temperature will lead to shorter life of the lithium battery, so the design of the iphone charger flow is 1A.
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The current required for charging the ipad is relatively large, requiring about 5V of current, so the maximum output of the ipad charger 2.1A current, such a current for the iphone is unacceptable, but will quickly damage the iphone battery.
The Ipad charger can charge the phone
There are two kinds of iPad charger, the old iPad charger is 5 volt voltage 2.4 ampere current output, this charger is an ordinary charger does not support the fast charge protocol, can be used as an ordinary charger to charge the phone. The new iPad supports the pd fast charge protocol, and uses a charger that supports the pd fast charge protocol. This charger charges the mobile phone with the general pd fast charge protocol, which is a fast charge appliance. The mobile phone does not support the fast charge protocol and can be used as an ordinary charger.