Power supply apparatus with protection function and redundant power supply system

A redundant power supply system comprising:

• a plurality of power supply apparatuses with protection functions, the power supply apparatuses connected in parallel and having a bus voltage and together outputting a direct current power,
• wherein the power supply apparatus comprises:
• a pulse width modulation control unit;
• a pulse width modulation detecting unit electrically connected to the pulse width modulation control unit;
• a switch unit electrically connected to the pulse width modulation detecting unit;
• and
• a feedback circuit electrically connected to the pulse width modulation control unit and the switch unit, the feedback circuit detecting a bus voltage,
• wherein the switch unit comprises:
• a secondary side rectifying switch subunit electrically connected to the pulse width modulation detecting unit;
• an output switch subunit electrically connected to the secondary side rectifying switch subunit, the pulse width modulation detecting unit and the feedback circuit;
• and
• a first capacitor electrically connected to the secondary side rectifying switch subunit and the output switch subunit,
• wherein when an output voltage of one of the power supply apparatuses is increased abnormally such that the bus voltage is increased abnormally, and the feedback circuit of the normal power supply apparatus detects that the bus voltage is increased abnormally, the feedback circuit of the normal power supply apparatus sends an informing signal to the pulse width modulation control unit;
• after the pulse width modulation control unit receives the informing signal, the pulse width modulation control unit adjusts a duty cycle of a pulse width modulation signal and sends the pulse width modulation signal to the pulse width modulation detecting unit;
• when the pulse width modulation detecting unit detects that the duty cycle of the pulse width modulation signal is less than a predetermined cycle, the pulse width modulation control unit turns off the output switch subunit to stop outputting power and to decrease the output voltage, and at the same time, the secondary side rectifying switch subunit is turned on, so that the output voltage of the normal power supply apparatus is not decreased to 0 volt.