Variable switching frequency power supply apparatus

A variable switching frequency power supply apparatus comprising:

• a main transformer;
• a voltage detection unit electrically connected to the main transformer;
• a pulse width modulation control unit electrically connected to the voltage detection unit;
• and
• a switch unit electrically connected to the pulse width modulation control unit and the main transformer,
• wherein the main transformer transforms an input voltage into an output voltage according to a switching frequency of the switch unit;
• the voltage detection unit detects the input voltage and then informs the pulse width modulation control unit;
• the pulse width modulation control unit is configured to control the switching frequency of the switch unit according to a voltage absolute value of the input voltage,
• wherein when the voltage absolute value of the input voltage is increasing and is larger than a first threshold voltage value, the pulse width modulation control unit is configured to control the switching frequency of the switch unit, so that the switching frequency of the switch unit is a first frequency,
• wherein when the voltage absolute value of the input voltage is increasing and is not larger than the first threshold voltage value, the pulse width modulation control unit is configured to control the switching frequency of the switch unit, so that the switching frequency of the switch unit is not changed,
• wherein when the voltage absolute value of the input voltage is decreasing and is smaller than a second threshold voltage value, the pulse width modulation control unit is configured to control the switching frequency of the switch unit, so that the switching frequency of the switch unit is a second frequency,
• wherein when the voltage absolute value of the input voltage is decreasing and is not smaller than the second threshold voltage value, the pulse width modulation control unit is configured to control the switching frequency of the switch unit, so that the switching frequency of the switch unit is not changed,
• wherein the first threshold voltage value is larger than the second threshold voltage value;
• the first frequency is smaller than the second frequency;
• the pulse width modulation control unit is configured to control the switching frequency of the switch unit by a hysteresis effect.