Power supply apparatus and image forming apparatus
The power supply apparatus includes a transformer, a switching unit provided on a primary side of the transformer and configured to perform switching operation for converting an input voltage resulting from rectification and smoothing of an AC voltage and outputting an output voltage from a secondary side of the transformer; a first detection unit configured to detect the output voltage, a feedback unit configured to generate a feedback voltage based on the voltage detected by the first detection unit; a control unit configured to control the switching operation of the switching unit based on the feedback voltage generated by the feedback unit; and a second detection unit configured to detect the AC voltage.
1. A power supply apparatus comprising:
a transformer configured to isolate a primary side and a secondary side;
a switching unit provided on the primary side of the transformer and configured to perform switching operation for converting an input voltage in which an AC voltage are rectified and smoothed and outputting an output voltage from the secondary side of the transformer;
a first detection unit configured to detect the output voltage;
a feedback unit configured to generate a feedback voltage based on the output voltage detected by the first detection unit;
a control unit configured to control the switching operation of the switching unit based on the feedback voltage generated by the feedback unit; and
a second detection unit configured to detect the AC voltage,
wherein the control unit performs the switching operation such that the higher the AC voltage detected by the second detection unit, the shorter a conduction time period of the switching unit corresponding to the feedback voltage and the smaller a variation amount of the conduction time period of the switching unit corresponding to a variation amount of the feedback voltage.
2. A power supply apparatus according to claim 1 , wherein the conduction time period of the switching unit is represented by a linear function whose variable is the feedback voltage, and each of a gradient and an intercept of the linear function includes an inverse of the AC voltage.
3. A power supply apparatus according to claim 1 , wherein the control unit sets the conduction time period of the switching unit at a constant value if the feedback voltage exceeds a predetermined value, and
the higher the AC voltage, the smaller the constant value.
4. A power supply apparatus according to claim 1 , wherein the power supply apparatus comprises a selection unit configured to select a target voltage of the output voltage, and
the control unit controls the conduction time period of the switching unit according to the target voltage.
5. A power supply apparatus according to claim 1 , wherein the feedback unit has a constant-voltage source.
6. A power supply apparatus according to claim 1 , wherein the switching unit includes a first switching element connected in series to a primary winding of the transformer and a second switching element connected in parallel to the primary winding of the transformer, and includes a capacitor connected in series to the second switching element and connected in parallel to the primary winding of the transformer along the second switching element,
the control unit controls turning on or off the first switching element and the second switching element based on the feedback voltage from the feedback unit, and
the control unit is capable of performing operation of alternately repeating a first period and a second period, the first period involving performing switching operation of selectively 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, and the second period involving suspending the switching operation.
7. An image forming apparatus comprising:
an image forming unit for forming an image; and
a power supply apparatus configured to power the image forming apparatus,
wherein the power supply apparatus comprises:
a transformer configured to isolate a primary side and a secondary side;
a switching unit provided on the primary side of the transformer and configured to perform switching operation for converting an input voltage in which an AC voltage are rectified and smoothed and outputting an output voltage from the secondary side of the transformer;
a first detection unit configured to detect the output voltage;
a feedback unit configured to generate a feedback voltage based on the output voltage detected by the first detection unit;
a control unit configured to control the switching operation of the switching unit based on the feedback voltage generated by the feedback unit; and
a second detection unit configured to detect the AC voltage,
wherein the control unit performs the switching operation such that the higher the AC voltage detected by the second detection unit, the shorter a conduction time period of the switching unit corresponding to the feedback voltage and the smaller a variation amount of the conduction time period of the switching unit corresponding to a variation amount of the feedback voltage.
8. An image forming apparatus according to claim 7 , wherein the conduction time period of the switching unit is represented by a linear function whose variable is the feedback voltage, and each of a gradient and an intercept of the linear function includes an inverse of the AC voltage.
9. An image forming apparatus according to claim 7 , wherein the control unit sets the conduction time period of the switching unit at a constant value if the feedback voltage exceeds a predetermined value, and
the higher the AC voltage, the smaller the constant value.
10. An image forming apparatus according to claim 7 , wherein the power supply apparatus comprises a selection unit configured to select a target voltage of the output voltage,
the control unit controls the conduction time period of the switching unit according to the target voltage, and
the image forming apparatus comprises a controller configured to output a signal directing the selection unit to select the target voltage of the output voltage.
11. An image forming apparatus according to claim 7 , wherein the feedback unit has a constant-voltage source.
12. An image forming apparatus according to claim 7 , wherein the switching unit includes a first switching element connected in series to a primary winding of the transformer and a second switching element connected in parallel to the primary winding of the transformer, and includes a capacitor connected in series to the second switching element and connected in parallel to the primary winding of the transformer along the second switching element,
the control unit controls turning on or off the first switching element and the second switching element based on the feedback voltage from the feedback unit, and
the control unit is capable of performing operation of alternately repeating a first period and a second period, the first period involving performing switching operation of selectively 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, and the second period involving suspending the switching operation.
13. An image forming apparatus according to claim 7 , wherein the image forming apparatus comprises:
a controller configured to control the image forming unit; and
a driving unit configured to drive the image forming unit,
wherein the power supply apparatus powers the controller or the driving unit.