Power supply apparatus and image forming apparatus

A power supply apparatus comprising:

• a transformer having a primary winding and a secondary winding;
• a first switching element connected in series to the primary winding of the transformer;
• a second switching element connected in parallel to the primary winding of the transformer;
• a capacitor connected in series to the second switching element and connected along with the second switching element in parallel to the primary winding of the transformer;
• a feedback unit configured to output a feedback voltage to a primary side according to a voltage induced in the secondary winding of the transformer;
• and
• a control unit configured to control turning on or off of the first switching element and the second switching element based on the feedback voltage,
• wherein the control unit is configured to perform switching operation of alternately turning on or off the first switching element and the second switching element before and after a dead time during which the first switching element and the second switching element are both turned off,
• wherein the power supply apparatus is capable of switching a state between a first state in which an output voltage output from the secondary winding is a first voltage and a second state in which the output voltage is a second voltage lower than the first voltage, and
• wherein in the first state, the control unit alternately repeats a control between a first control of varying a frequency of the switching operation within a predetermined range, and a second control of varying the frequency within a range narrower than the predetermined range or a third control of controlling the frequency to be a constant frequency.

An image forming apparatus comprising:

• an image forming unit configured to form an image on a recording material;
• and
• a power supply apparatus configured to power the image forming apparatus,
• the power supply apparatus including:
• a transformer having a primary winding and a secondary winding;
• a switching element connected in series to the primary winding of the transformer;
• a feedback unit configured to output a feedback voltage to a primary side according to a voltage induced in the secondary winding of the transformer;
• and
• a control unit configured to control switching operation of turning on or off the switching element based on the feedback voltage,
• wherein the power supply apparatus is capable of switching a state between a first state in which an output voltage output from the secondary winding is a first voltage and a second state in which the output voltage is a second voltage lower than the first voltage, and
• wherein in the second state, the control unit alternately repeats a control between a first control of varying a frequency of the switching operation within a predetermined range, and a second control of varying the frequency within a range narrower than the predetermined range or a third control of controlling the frequency to be a constant frequency.

An image forming apparatus comprising:

• an image forming unit configured to form an image on a recording material;
• and
• a power supply apparatus configured to power the image forming apparatus,
• the power supply apparatus including:
• a transformer having a primary winding and a secondary winding;
• a switching element connected in series to the primary winding of the transformer;
• a feedback unit configured to output a feedback voltage to a primary side according to a voltage induced in the secondary winding of the transformer;
• and
• a control unit configured to control switching operation of turning on or off the switching element based on the feedback voltage,
• wherein the control unit alternately repeats a control between a first control of varying a frequency of the switching operation within a predetermined range, and a second control of varying the frequency within a range narrower than the predetermined range or a third control of controlling the frequency to be a constant frequency.