Power supply apparatus and image forming apparatus

An image forming apparatus, comprising:

• an image forming unit configured to form an image;
• and
• a power supply configured to supply a voltage to the image forming unit,
• the power supply comprising:
• a transformer;
• a switching element connected to a primary side of the transformer;
• a first line connected to a secondary side of the transformer, the first line configured to output a voltage of a first polarity;
• a second line connected to the secondary side of the transformer, the second line configured to output a second polarity voltage whose polarity is opposite to the first polarity;
• a first diode connected to the first line in a predetermined direction;
• a first capacitor connected to the first line between a voltage output side of the first diode and a ground;
• a second diode connected to the second line in a direction opposite to the predetermined direction of the first diode;
• a second capacitor connected to the second line between a voltage output side of the second diode and the ground;
• a resistor element connected to the first line on an output side of the first diode;
• and
• a control unit configured to control a drive frequency of the switching element to control a voltage output from the second line constant.