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A USB cable can be used to transfer data and/or charge a device. For example, a printer can be connected to the computer via a USB cable in order to transfer a document to be printed. For charging, we use USB cables every day, e.g. for smartphones. The most common USB cable types for charging mobile devices such as mobile phones are USB-A to USB-C, Micro-USB and Lightning (Apple devices).
Four wires are required in a USB cable. Two wires transmit the data, the other two supply the connected device with a voltage of 5 V. Devices complying with USB specifications may draw up to 100 mA or 500 mA from the bus, depending on how much the port to which they are connected to can supply. Devices with a power of up to 2.5 W can therefore be supplied via the bus. Depending on the cable length, the meeting point between the two power supplies must be adapted to comply with the permissible voltage drop limit; extension cables are therefore not standard.