USB interfaces can be used to charge batteries from small mobile devices such as smartphones, cell phones or digital cameras. This functionality is called USB Battery Charging( USB-BC) and is supported by the USB 2.0 and USB 3.0 versions, but only with powers of 2.5 W and 4.5 W, respectively. Higher charging powers of up to 100 W are achieved with USB Power Delivery (USB- PD).
USB Power Delivery is a specification of the USB Implementers Forum( USB-IF). The UPD protocol defines how the current and voltage are negotiated across the USB power pins. The lowest currents and voltages are always applied first.
In total, USB-PD distinguishes between five different Power Delivery profiles. The PD profile with the lowest power is profile 1 with a power of 10 W, or 5 V with 2 A. Like USB-BC, this profile is suitable for small mobile devices, whereby the specified PD power exceeds the BC power by double. The other profile power ratings go over 18 W, 36 W and 60 W to 100 W. The highest power values depend on the USB version and the USB connector. Thus, the power profile of 20 V and 3 A can still be transmitted via micro USB plugs, the highest power of 100 W only from USB 3.1 via the USB C plug and the corresponding USB cable.
In the USB-PD topology, there are devices that act as consumers, the so-called consumers, others that supply the energy, these are the providers, and still others that combine both functions in themselves. If energy is supplied from a provider to a consumer, then certain characteristic values such as the maximum power are negotiated in advance between the partners.
In the case of the USB-C interface, which can transmit a charging power of 15 W, variable supply voltage can be used in the power delivery function and the current intensity can be increased from 3 A at 5 V to 5 A. USB-C supports the five profiles specified by the USB Implementers Forum (USB-IF) and can transmit a power of 100 W with 20 V and 5 A in profile 5.