This publication describes Qi-based wireless-charging protocols that enable and protect user equipment (UE) (e.g., smartphones) that can act as power transmitter (Tx) or receivers (Rx). The UE acting as a Tx, herein referred to as "Tx UE," and a UE acting as an Rx, herein referred to as "Rx UE," can safely enter and maintain a power-transfer phase without causing wireless-charging disconnection due to power limitations of the Tx UE or other system errors, such as out of target output rectified voltage (VRECT), output voltage (VOUT), or control error packet (CEP). The described Qi-based wireless-charging protocols can accomplish the power-transfer phase using two methods—utilizing a bi-directional communication between the Tx UE and the Rx UE or without communication from the Tx UE to Rx UE. Power transferring using bi-directional communication requires that both the Tx UE and the Rx UE support the required firmware and/or software to enable power transferring without wireless-charging disconnection. On the other hand, power transferring without Tx-to-Rx bi-directional communication does not require that both the Tx UE and the Rx UE support the required firmware and/or software to enable power transferring without wireless-charging disconnection, as long as the Rx UE supports firmware and/or software that can monitor the parameters VRECT, VOUT, and/or CEP, and adjust (lower) the current (Amperes) demand until it reaches a charging current that matches the current being supplied by the Tx UE.
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Jia, Liang and Polu, Nagesh, "Implementing Transmitter Current Limit During Wireless Charging", Technical Disclosure Commons, (August 12, 2019)