A power supply unit (PSU) configured to provide electrical power to an electronic device. The PSU may include a PSU control circuit configured to, via a power meter, detect that electrical power conveyed to the electronic device is above a timer starting threshold. In a first charging mode with a first predetermined charging duration, the PSU control circuit may control the PSU to convey electrical power to the electronic device with a first power ceiling. Subsequently to the first predetermined charging duration elapsing, in a second charging mode with a second predetermined charging duration, the PSU control circuit may control the PSU to convey electrical power to the electronic device with a second power ceiling that is lower than the first power ceiling. Subsequently to the second predetermined charging duration elapsing, the PSU control circuit may control the PSU to return to the first charging mode.

Techniques are provided for improving power efficiency of a multiphase direct current (DC)-DC voltage converter configured to provide DC power to a time domain duplexing radio by enabling a number of phases during a downlink subframe and disabling the number of phases on or after cessation of the downlink subframe.

An air conditioner includes a refrigerant circuit, a main board, and a backup board. The refrigerant circuit includes a shutoff valve that shuts off a refrigerant flow. The main board includes a microcomputer that controls the shutoff valve. The backup board supplies power from a capacitor to the main board. The backup board includes a charging circuit that receives power supply from an outside and charges the capacitor. The microcomputer detects whether the backup board is connected to the main board based on a voltage on the upstream side of the charging circuit.