Power supply apparatus and image forming apparatus
A power supply apparatus including a switching element configured to supply or cut off electric power to a primary coil of a transformer by a switching operation, and a control unit configured to control the switching operation. The control unit is configured to perform intermittent control of repeating a switching period for performing the switching operation and a stop period for stopping the switching operation. In the switching period, when the control unit performs the switching operation a predetermined number of times, the switching period is transitioned to the stop period. In the stop period, when the control unit determines that a voltage output from a secondary coil of the transformer falls below a target voltage, the stop period is transitioned to the switching period. The control unit is configured to change the switching operation based on a length of the stop period.
1 . A power supply apparatus, comprising:
a transformer including a primary coil and a secondary coil configured to generate a voltage based on electric power supplied to the primary coil;
a switching element configured to supply the electric power to the primary coil by a switching operation of alternately switching between an ON state and an OFF state;
a feedback unit configured to feed back a signal based on the voltage; and
a control unit configured to control the switching operation and perform an intermittent control of alternately repeating a switching period for performing the switching operation and a stop period in which the switching element is in the OFF state, wherein, in case the control unit detects, based on the signal, that a value of the voltage is lower than a threshold value, the control unit controls the intermittent control so as to transition from the stop period to the switching period,
wherein, in a case where the intermittent control is performed in an order of a first stop period, a first switching period, a second stop period, and a second switching period and the second stop period is shorter than the first stop period, the control unit controls the switching operation in the second switching period such that an On-Duty in the second switching period is greater than an On-Duty in the first switching period, and
wherein in a case where the second stop period is longer than the first stop period, the control unit controls the switching operation in the second switching period such that the On-Duty in the second switching period is smaller than the On-Duty in the first switching period.
2 . The power supply apparatus according to claim 1 , wherein in a case where the second stop period is shorter than the first stop period, the control unit controls the switching operation in the second switching period such that the On-Duty in the second switching period is greater than the On-Duty in the first switching period and a switching cycle of the switching element in the first switching period is equal to a switching cycle of the switching element in the second switching period.
3 . The power supply apparatus according to claim 1 , further comprising:
a first rectifying/smoothing portion configured to rectify and smooth an AC voltage input to the first rectifying/smoothing portion, and to output a rectified and smoothed voltage to the primary coil;
a second rectifying/smoothing portion configured to rectify and smooth a voltage induced on an auxiliary coil of the transformer; and
a voltage divider which includes a voltage divider resistor, and is configured to divide a voltage output from the second rectifying/smoothing portion by the voltage divider resistor, and to output a voltage to the control unit,
wherein the control unit is configured to determine the On-Duty in the second switching period based on the voltage supplied from the voltage divider.
4 . The power supply apparatus according to claim 3 , wherein the control unit is configured to determine the On-Duty in the second switching period based on the voltage supplied from the voltage divider at a start time of the second stop period.
5 . The power supply apparatus according to claim 1 , wherein the control unit is configured to vary a length of the second switching period in accordance with a length of the first stop period so that a sum of a length of the first switching period and a length of the first stop period is equal to a sum of the length of the second switching period and the length of the second stop period, and to change a number of times of the switching operation of the switching element in the second switching period in accordance with the varied length of the second switching period.
6 . The power supply apparatus according to claim 5 , wherein a frequency component of a multiple of a frequency being a reciprocal of a period of time obtained by summing the length of second the switching period and the length of the second stop period is apart from a resonance frequency of the transformer.
7 . The power supply apparatus according to claim 1 , wherein the switching element is a first switching element, the power supply apparatus further comprising:
a second switching element which is connected in parallel to the primary coil of the transformer and is configured to be controlled by the control unit; and
a capacitor which is connected in series to the second switching element, and is connected, together with the second switching element, in parallel to the primary coil of the transformer,
wherein in the switching period, the control unit is configured to perform the switching operation of alternately turning on or off the first switching element and the second switching element through intermediation of a dead time in which both of the first switching element and the second switching element are turned off, and in the stop period, the control unit is configured to stop the switching operation, and
wherein in a transition from the switching period to the stop period, the control unit is configured to turn on the second switching element and then transition to the stop period, and also in a transition from the stop period to the switching period, the control unit is configured to turn on the second switching element and then transition to the switching period.
8 . The power supply apparatus according to claim 7 , wherein the control unit is configured to determine a time for turning on the second switching element in the transition from the switching period to the stop period based on a length of the stop period.
9 . An image forming apparatus, comprising:
the power supply apparatus according to claim 1 ;
an image forming portion configured to form an image on a recording material; and
a controller configured to control the image forming portion,
wherein the power supply apparatus is configured to supply electric power to the image forming portion and the controller,
wherein the controller is configured to control the image forming portion to be switchable among a print state for forming the image on the recording material, a standby state of being ready to transition to the print state, and a sleep state for performing an intermittent control.