Power adapter power delivery

A method for operating a universal serial bus power delivery (USB-PD) power adaptor comprising:

• operating a first buck circuit comprising a first switch connected between a supply voltage terminal and a first USB port based on one of a first target voltage or a second target voltage for the first USB port and a supply voltage at the supply voltage terminal, wherein:
• responsive to the first target voltage being less than the supply voltage plus an offset voltage, operating the first buck circuit in a variable-buck-input mode to control the first switch according to a first duty cycle based on the first target voltage and the supply voltage to generate the first target voltage at the first USB port;
• and
• responsive to the second target voltage being equal to the supply voltage plus the offset voltage, operating the first buck circuit in a buck-bypass mode to maintain an on state of the first switch to generate the second target voltage at the first USB port.

A universal serial bus power delivery (USB-PD) power adaptor comprising:

• USB ports;
• a flyback-converter operable to receive and convert a first voltage to a second voltage;
• buck circuits connected between the flyback-converter and the USB ports;
• and
• a USB-PD controller connected to the flyback-converter and configured to:
• receive target voltages for the USB ports;
• determine a value for the second voltage of the flyback converter based on a greatest of the target voltages;
• responsive to a first target voltage for a first selected buck circuit of the buck circuits being less than the second voltage plus an offset voltage, operating the first selected buck circuit in a variable-buck-input mode according to a duty cycle based on the first target voltage for the first selected buck circuit and the second voltage to generate the first target voltage for the first selected buck circuit at a first USB port of the USB ports associated with the first selected buck circuit;
• and
• responsive to a second target voltage for a second selected buck circuit of the buck circuits being less than the second voltage plus the offset voltage, operating the second selected buck circuit in a buck-bypass mode according to a duty cycle of 100% to generate the second target voltage for the second selected buck circuit at a second USB port of the USB ports associated with the second selected buck circuit.