Power bank are popular for charging smartphones, mobile tablet devices, and other USB charged devices. They can also be used as a power supply for various USB powered devices such as lights and small fans. A powerbank is a portable device that can supply power from its built-in batteries through a USB port. They usually recharge with USB power supply. Technically, a powerbank consists of rechargeable Lithium-ion or Lithium-Polymer batteries installed in a protective casing, guided by a printed circuit board (PCB)which provides various protective and safety measures. Because a lithium ion battery operates at 3.7V nominal, voltage conversion circuitry is needed to drop the 5V USB input and raise the output back up to 5V.
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