An out-door unit (600) with multiple ports comprises a plurality of circuit blocks, a DC-DC converter and a plurality of ports (601 ... 604). The DC-DC converter is configured to provide current to the plurality of circuit blocks. The plurality of ports is connected to a plurality of in-door units (21 ... 24) respectively via a diode and provides current from the plurality of in-door units to the DC-DC converter via a diode respectively. At least one of the plurality of ports is connected to a first circuit block of the plurality of circuit blocks to provide current to the first circuit block.