Isolated converter with output voltage protection and adjustable protection threshold

A power supply unit configured to provide an output voltage from an output end to supply power to a load, the power supply unit comprising a transformer and an auxiliary power circuit, the auxiliary power circuit coupled to the transformer to provide a working voltage, and the power supply unit further comprising:

• an over-power protection circuit, comprising:
• a switch comprising a first end and a second end, the first end coupled to a power switch and a controller of the power supply unit, and the controller configured to set an over-power protection value of the power supply unit according to a voltage at the first end;
• a first resistor, one end of the first resistor coupled to the second end;
• a second resistor, one end of the second resistor coupled to the first end, and the other end of the second resistor coupled to the other end of the first resistor;
• and
• a regulator circuit coupled to a control end of the switch, and configured to receive the working voltage,
• wherein, when the output voltage is at a first level, the over-power protection circuit is configured to turn on the switch according to the output voltage with the first level to provide a first resistance value based on the first resistor and the second resistor in parallel, so as to adjust the over-power protection value to a first value;
• when the output voltage is at a second level less than the first level, the over-power protection circuit is configured to turn off the switch according to the output voltage with the second level to provide a second resistance value of the second resistor, so as to adjust the over-power protection value to a second value, and
• wherein, when the output voltage is at the first level, the working voltage provided by the auxiliary power circuit is at a third level corresponding to the first level, and the regulator circuit is configured to establish a control voltage at the control end according to the working voltage of the third level being higher than a clamping voltage of the regulator circuit;
• when the output voltage is at the second level, the working voltage provided by the auxiliary power circuit is at a fourth level corresponding to the second level, and the regulator circuit is configured to limit the voltage of the control end to be lower than a threshold voltage according to the working voltage of the fourth level being lower than the clamping voltage.