JP5045361B2 - Power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a power supply device for a charging device having a constant current AC output, and an image forming apparatus including the power supply device.

  An image forming apparatus such as a copying machine or a printer using an electrophotographic process applies a bias voltage to a peripheral surface of a photosensitive drum rotating around a predetermined axis via a charging roller so that the peripheral surface is made uniform. It is designed to be charged. By irradiating the uniformly charged surface of the photosensitive drum with a laser beam based on image information, the charged state of the laser beam irradiated portion is eliminated and an electrostatic latent image is formed. A toner image is formed by supplying toner toward the electrostatic latent image.

  In the contact charging method using this charging roller, a method is used in which a bias in which an alternating current is superimposed on a direct current voltage is applied. Only by applying a DC voltage, a current flows only at a low resistance on the photoconductor, so that it cannot be uniformly charged. Further, when the surface of the photosensitive member is locally soiled, there arises a problem that only that portion is not charged. For this reason, as shown in FIG. 1, a bias in which an alternating current is superimposed on a direct current voltage is applied to the charging roller to uniformly charge the surface of the photoreceptor.

In such a charge control system, a charging roller used for charging a photosensitive member is configured by covering a surface of a metal core made of metal such as stainless steel with a conductive layer made of conductive synthetic rubber or the like. For this reason, conversion to the impedance of the charging roller occurs depending on the surrounding environment. For example, in cold regions, synthetic rubber shrinks and increases impedance, and when used in a high temperature environment, synthetic rubber loosens and impedance decreases.
As described above, constant current control is performed on the alternating current. Therefore, when the impedance of the charging roller increases, the voltage applied to the charging roller must be set high, and the power consumption of the power supply device also increases.

  Patent Document 1 discloses a technique for shutting down power supplied to a load when the load is abnormal. Further, in Patent Document 2, an AC output is superimposed on a DC output, and the output of the high-voltage power supply device is intermittently output in the high-voltage power supply device when the AC output is overcurrent.

JP-A-9-016033 JP 2000-330431 A

  An object of this invention is to provide the power supply device which can reduce the power consumption at the time of the load abnormality of a charging device.

In order to achieve such an object, the invention according to claim 1 is a power supply device used in a charger of an image forming apparatus, wherein charging is performed by superimposing a constant voltage DC output on a constant current AC output and supplying the same to the charger. A power supply for charging, a detection circuit for detecting a load abnormality of the charging power supply, a control circuit for controlling the charging power supply so that an AC output supplied to the charger becomes a constant voltage, and a power supply for the charging power supply. An input cutoff circuit that shuts off the input, and when a load abnormality is detected by the detection circuit, the AC output supplied to the charger by the control circuit and the input cutoff circuit becomes a constant voltage intermittent output. Adopt the configuration to control.

  According to a second aspect of the present invention, in the first aspect of the invention, there is provided selection means for selecting a cycle of the input cutoff circuit depending on a frequency of an input signal that determines a frequency of the constant current AC output.

According to a third aspect of the present invention, in the first or second aspect of the invention, the input cut-off circuit turns on and off the input of the charging power source based on a detection voltage of the constant current AC output.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the input cutoff circuit is provided in common for a plurality of charging power sources.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects of the present invention, a detection circuit that detects a current of the constant voltage DC output, and the input cutoff based on a detection current of the detection circuit It has a control means which controls the cycle which a circuit turns on and off.

According to a sixth aspect of the present invention, there is provided a power supply device for use in a charger of an image forming apparatus, the charging power supply for superimposing a constant voltage direct current output on a constant current alternating current output to the charger, and the charging device. A detection circuit for detecting a load abnormality of the power supply, a control circuit for controlling the charging power supply so that the AC output supplied to the charger becomes a constant voltage, and a control signal for cutting off the control signal of the charging power supply An AC output supplied to the charger by the control circuit and the control signal cutoff circuit when the load abnormality is detected by the detection circuit. Adopt the configuration.

According to a seventh aspect of the invention, in the sixth aspect of the invention, there is provided selection means for selecting a cycle in which the control signal cutoff circuit is turned on and off according to the frequency of the control signal.

The invention according to claim 8 is the invention according to claim 6 or 7, wherein the control signal cut-off circuit turns the control signal on and off based on a detection voltage of the constant current AC output.

According to a ninth aspect of the present invention, in the invention according to any one of the sixth to eighth aspects, the control signal cutoff circuit is provided in common for a plurality of charging power sources.

  According to a tenth aspect of the present invention, in the invention according to any one of the third, fourth, sixth, and eighth aspects, the detection circuit detects a current of the constant voltage DC output, and a detection current of the detection circuit. And a control means for controlling a cycle in which the control signal cutoff circuit is turned on and off.

  An eleventh aspect of the invention includes the power supply device according to any one of the first to tenth aspects, and a charging device that is charged by a power source supplied from the power source device and charges an image carrier. Is adopted.

According to the first and sixth aspects of the present invention, when load abnormality occurs, the AC output is changed from constant current output to constant voltage control, so that the power consumption of the power supply at the time of load abnormality does not have this configuration. It can be reduced in comparison.

According to the second and seventh aspects of the invention, even when the process speed is changed, it is possible to notify the image that notifies when the load is abnormal with substantially the same image.

According to the third and eighth aspects of the invention, it is possible to detect an abnormality in the constant current AC output and shift to the constant voltage intermittent control.

According to the fourth and ninth aspects of the present invention, it is not necessary to provide a plurality of input cutoff circuits, the apparatus configuration can be simplified, and the apparatus cost can be reduced.

According to invention of Claim 5, 10 , constant voltage intermittent control can be performed based on a constant voltage DC output.

  Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 shows a configuration of the power supply device 1 for the image forming apparatus. The power supply device 1 of this embodiment includes an AC output circuit unit having a transformer 25 and a DC output circuit unit having a transformer 60.
In addition to the transformer 25, the AC output circuit section includes switching transistors Tr2 and Tr3, a sine wave generation circuit 20, a constant current control circuit 21, a D / A conversion / PWM conversion circuit 22, a constant voltage control circuit 23, a current A detection circuit 30, a voltage detection circuit 40, a comparator 41, and the like are included.
In addition to the transformer 60, the DC output circuit section includes a switching transistor Tr4, a drive circuit 61, a constant voltage control circuit 62, a DC voltage detection circuit 65, a D / A conversion / PWM conversion circuit 70, and the like.
The power supply device 1 further includes an input cutoff circuit 10, an input on / off circuit 50, and a frequency determination circuit 55.

The sine wave generation circuit 20 receives a clock signal input from the outside and a control signal from the constant current control circuit 21 or the constant voltage control circuit 23, and generates a sine wave signal for switching the transistor Tr2 and the transistor Tr3. Generate.
The clock signal input from the outside to the sine wave generation circuit 20 is a signal for setting the frequency of the AC output applied to the charging roller. Based on this clock signal, the sine wave generation circuit 20 determines the frequency of the sine wave signal output to the bases of the transistors Tr2 and Tr3.
The sine wave generation circuit 20 adjusts the Vpp (peak value) of the sine wave signal to be generated according to the control of the constant current control circuit 21 or the constant voltage control circuit 23. When receiving the control from the constant current control circuit 21, the Vpp of the sine wave signal is adjusted so that the effective value of the alternating current applied to the charging roller is constant. Further, when receiving the control from the constant voltage control circuit 23, the Vpp of the sine wave signal is adjusted so that the effective value of the AC voltage applied to the charging roller is constant.

The D / A conversion / PWM conversion circuit 22 is supplied with an AC on / off variable signal for setting the on / off setting of the alternating current applied to the charging roller and the current value of the alternating current during constant current control. The
The D / A conversion / PWM conversion circuit 22 first converts a digital AC on / off variable signal into an analog signal, and performs PWM (Pulse-Width Modulation) conversion so that the duty of the converted analog signal matches the duty of the digital signal. I do.
The converted analog AC on / off variable signal is output to the comparator 24.

The current detection circuit 30 is connected to the secondary winding side of the transformer 25, and includes a half-wave rectification circuit having a diode D1 and a capacitor C4, and a current / voltage conversion circuit having resistors R4, R5, and R6. Have.
A half-wave rectifier circuit composed of a diode D1 and a capacitor C4 detects the positive value of the alternating current appearing on the secondary winding side of the transformer 25, and the positive value of the alternating current detected by the current / voltage conversion circuit. Is converted into a voltage value (hereinafter, this value is referred to as a voltage conversion value).
The voltage conversion value detected by the current detection circuit 30 is output to the constant current control circuit 21 via the comparator 24.

The comparator 24 sets the threshold voltage based on the pulse width of the analog AC on / off variable signal output from the D / A conversion / PWM conversion circuit 22. The comparator 24 set with the threshold voltage compares this threshold voltage with the voltage conversion value output from the current detection circuit 30. When the voltage conversion value from the current detection circuit 30 is smaller than the threshold voltage, the comparator 24 outputs the voltage conversion value of the current detection circuit 30 to the constant current control circuit 21. When the voltage conversion value of the current detection circuit 30 becomes equal to or higher than the threshold voltage, the comparator 24 does not output the voltage conversion value of the current detection circuit 30 to the constant current control circuit 21.
The output of the constant voltage control circuit 23 is connected to the comparator 24 via a diode. Since the voltage of the control signal output from the constant voltage control circuit 23 is higher than the voltage of the voltage conversion value output from the current detection circuit 30, when the control signal is output from the constant voltage control circuit 23, the comparator 24 Is supplied with this control signal.
When the comparator 24 receives the control signal output from the constant voltage control circuit 23, the comparator 24 always supplies the control signal to the constant current control circuit 21 regardless of the AC on / off variable signal output from the D / A conversion / PWM conversion circuit 22. Output.
The constant current control circuit 21 is a sine wave signal generated by the sine wave generation circuit 20 based on the voltage conversion value detected by the current detection circuit 30 so that the effective value of the alternating current applied to the charging roller is constant. Is controlled.
The constant current control circuit 21 sets the Vpp of the sine wave signal generated by the sine wave generation circuit 20 to the maximum value when the control signal from the constant voltage control circuit 23 is input.

The voltage detection circuit 40 is connected to the secondary winding side of the transformer 25, and includes an AC voltage dividing circuit having capacitors C5 and C6, a half-wave rectifier circuit having diodes D2 and D3, and a capacitor C7. have.
The AC voltage is divided by capacitors C5 and C6 connected to the secondary winding side of the transformer 25, and the divided low voltage AC voltage is half-wave rectified by a half-wave rectifier circuit to obtain the positive AC voltage value. To do.
The detection voltage of the voltage detection circuit 40 is output to the comparator 41. The comparator 41 compares the detection voltage of the voltage detection circuit 40 with the reference voltage, and outputs a signal at a predetermined level to the constant voltage control circuit 23 and the input on / off circuit 50 when the detection voltage becomes higher than the reference voltage.
The constant voltage control circuit 23 makes the effective value of the AC voltage applied to the charging roller constant based on a signal of a predetermined level output from the comparator 41 (representing the detection voltage value of the voltage detection circuit 40). Vpp of the sine wave signal generated by the sine wave generation circuit 20 is controlled. During constant voltage control, Vpp of the sine wave signal is set to the maximum value.

As shown in FIG. 2, the input on / off circuit 50 has resistors R7 and R8, an electrolytic capacitor C8, a comparator 51, and voltage sources Va and Vb. The voltage source Va is set to a value higher than Vb (Va> Vb).
The input on / off circuit 50 stores a signal of a predetermined level output from the comparator 41 in the electrolytic capacitor C8. When the voltage of the electrolytic capacitor C8 becomes higher than the voltage source (Va or Vb), the input cutoff circuit 10 is turned on. Outputs a signal to switch off.

The frequency determination circuit 55 receives a clock signal and determines whether or not the frequency of the clock signal is higher than a reference frequency, for example, 1000 Hz. When the frequency of the clock signal is higher than the reference frequency, the frequency determination circuit 55 outputs a signal for switching the switch 52 of the input on / off circuit 50 to the voltage Va side. When the frequency of the clock signal is lower than the reference frequency, the frequency determination circuit 55 outputs a signal for switching the switch 52 of the input on / off circuit 50 to the voltage Vb side.
When the frequency of the clock signal is higher than a reference frequency, for example, 1000 Hz, the low voltage Vb is connected to the switch 52 in order to set a short time for the input cutoff circuit 10 to switch on and off the 24V power supply. . Further, when the frequency of the clock signal is lower than the reference frequency, Va having a high voltage is connected to the switch 52 in order to set the on / off switching time of the input cutoff circuit 10 to be long.

  When the voltage of the electrolytic capacitor C8 becomes higher than Va or Vb input as the reference voltage, the comparator 51 outputs a signal for switching the input cutoff circuit 10 on and off. For this reason, the on / off cycle of the input cutoff circuit 10 can be changed by changing the voltage source (Va or Vb).

The input cutoff circuit 10 is a circuit for turning on and off the supply of 24V power to the transistor Tr2, and includes a transistor Tr1 connected to the 24V power supply, an electrolytic capacitor C1 and a resistor R1 connected between the emitter and base of the transistor Tr1. And resistors R2 and R3 connected in series to the base of the transistor Tr1. The end of the resistor R3 opposite to the connection point with R2 is grounded. The output of the input on / off circuit 50 is connected to the connection point between the resistors R2 and R3.
The input cutoff circuit 10 switches on and off the transistor Tr1 that switches the 24V power supply according to the output of the input on / off circuit 50.

  The DC output circuit unit is connected to the low voltage side of the secondary winding side of the transformer 25 that generates an AC current. By supplying a voltage to the base of the transistor Tr4 by the drive circuit 61, a bias in which a DC voltage is superimposed on an AC current is generated on the high voltage output side of the secondary winding of the transformer 25.

The DC output circuit section is provided with a DC voltage detection circuit 65, a constant voltage control circuit 62, and a D / A conversion / PWM conversion circuit 70.
In the DC voltage detection circuit 65, resistors R9 and R10 and a capacitor C9 are connected in series. The DC voltage detection circuit 65 detects a DC voltage generated in the secondary side winding of the transformer 25.
The D / A conversion / PWM conversion circuit 70 receives a DC on / off variable signal for setting an on timing and an off timing of a DC voltage from the outside. The D / A conversion / PWM conversion circuit 70 first converts a digital DC on / off variable signal into an analog signal, and performs PWM conversion so that the duty of the converted analog signal matches the duty of the digital signal.
The converted analog DC on / off variable signal is output to the comparator 63.

  The comparator 63 sets the threshold voltage based on the pulse width of the analog DC on / off variable signal output from the D / A conversion / PWM conversion circuit 70. The comparator 63 set with the threshold voltage compares this threshold voltage with the detection voltage of the DC voltage detection circuit 65. When the detection voltage of the DC voltage detection circuit 65 is smaller than the threshold voltage, the comparator 63 outputs the detection voltage of the DC voltage detection circuit 65 to the constant voltage control circuit 62. Further, when the detection voltage of the DC voltage detection circuit 65 becomes equal to or higher than the threshold voltage, the comparator 63 does not output the detection voltage of the DC voltage detection circuit 65 to the constant voltage control circuit 62.

  The constant voltage control circuit 62 controls the drive circuit 61 based on the detection voltage of the DC voltage detection circuit 65 and performs control so that the DC voltage generated on the secondary winding side of the transformer 60 is constant.

In FIG. 3, the whole structure of the power supply device 1 and the wiring structure of a power supply line are shown. The power supply device 1 shown in FIG. 2 is provided for each image forming color of Y (yellow), M (magenta), C (cyan), and K (black). The power supply device 1 for each color includes an AC drive circuit such as a transformer that generates an AC output, an AC control circuit unit that controls the AC drive circuit, a DC drive circuit such as a transformer that generates a DC output, and a DC drive circuit. And a DC control circuit unit to be controlled. The AC control circuit section corresponds to the sine wave generation circuit 20, the constant current control circuit 21, the constant voltage control circuit 23, the D / A conversion / PWM conversion circuit 22 and the like shown in FIG.
The DC control circuit section corresponds to the constant voltage control circuit 62, the drive circuit 61, etc. shown in FIG.
The power supply line includes a drive circuit unit 24V line for supplying 24V power to the drive circuit unit for each color and a control circuit unit 24V power line for supplying 24V power to the control circuit unit for each color.

When the voltage detection circuit 40 detects an abnormality in the AC output of the transformer 25 and detects that there is an abnormality in the load, the power supply device 1 of the present embodiment uses the constant current control circuit 21 to control the AC output of the transformer 25. To constant voltage control by the constant voltage control circuit 23.
When the voltage detection circuit 40 detects that the AC output of the transformer 25 is abnormal, the input cutoff circuit 10 turns on / off the 24V power supplied to the transistor Tr2. By making the alternating current output of the transformer 25 constant voltage intermittent control, image quality defects are caused in the formed image.
Further, the cycle (setting of on time and off time) at which the input cutoff circuit 10 turns on and off the 24V power supply is configured to be changeable according to the frequency of the clock signal. When the frequency of the clock signal is higher than a reference frequency (for example, 1000 Hz), the ON time and the OFF time are set to be short to increase the number of times the AC output is supplied to the primary winding side of the transformer 25.
The externally input clock signal is a signal that determines the process speed of the image forming apparatus, but in charging control, the AC output supplied to the charging roller must be increased in proportion to the process speed of the image forming apparatus. . In the charge control using the discharge phenomenon, it is necessary to flow a constant alternating current to the charging roller. Therefore, when the process speed increases, the number of times of flowing alternating current to the charging roller, that is, the frequency must be increased.
For example, when the clock frequency is 100 mm / sec (800 Hz), the on time of the input on / off circuit 50 is 0.2 seconds and the off time is 2 seconds. When the clock frequency is 200 mm / sec (1600 Hz), the on time of the input on / off circuit 50 is 0.1 seconds and the off time is 1 second.
By setting the input on / off circuit 50 in such a manner, an image formed when the load is abnormal is output at a substantially constant value even if the process speed is different.

The operation timing of the power supply device 1 shown in FIG. 2 will be described with reference to FIG.
When the 24V power supply is input from the 24V power supply line, the transistor Tr1 is normally turned on, so that the voltage level at point B shown in FIG. 2 becomes 24V, and the 24V power supply is supplied to the switching transistors Tr2 and Tr3 of the transformer 25.
The sine wave generation circuit 20 to which the clock signal is externally input generates a sine wave signal to be supplied to the bases of the transistors Tr2 and Tr3 under the control of the constant current control circuit 21. Note that the frequency of the sine wave signal is generated based on the frequency of the clock signal. The constant current control circuit 21 starts operating when an AC on / off variable signal is externally input and a detection value of the current detection circuit 30 is output from the comparator 24.
When the transistors Tr2 and Tr3 are turned on by the sine wave generation circuit 20, an AC output is generated on the secondary winding side of the transformer 25, and is superimposed on the DC output generated by the DC output circuit unit and supplied to the charging roller.

Further, when an abnormality occurs in the load and the contact between the charging roller and the power supply device 1 is opened, the voltage detection circuit 40 detects an abnormality in the AC output of the transformer 25. When the voltage detection circuit 40 detects a load abnormality, as shown in FIG. 4, the voltage at the point C shown in FIG. 2 becomes high level.
The input on / off circuit 50 stores a signal of a predetermined level output from the comparator 41 in the electrolytic capacitor C8. When the voltage of the electrolytic capacitor C8 becomes higher than the voltage source (Va or Vb), the input on / off circuit 50 outputs a signal for switching on and off of the input cutoff circuit 10 (the voltage at the point D shown in FIG. 4). Level). When the transistor Tr1 of the input cutoff circuit 10 is turned on and off by the input on / off circuit 50, the output of the power supply device 1 is also periodically turned on and off as shown in FIG. This causes image quality defects in the image formed by the image forming apparatus.

A second embodiment of the present invention will be described with reference to the accompanying drawings.
This embodiment is an embodiment suitable for use in a power supply device for a multicolor image forming apparatus. This embodiment is a power supply device for C (cyan), M (magenta), Y (yellow), and K (black), and has an input cutoff circuit 10 and an input on / off circuit 50 in common. FIG. 5 shows the configuration of the power supply device 1 for the first color (any one of C, M, Y, and K), and FIG. 6 shows the configuration of the power supply devices for the second to fourth colors. The power supply device for the first color shown in FIG. 5 is provided with the input cutoff circuit 10 and the input on / off circuit 50. The other power supply devices for the second to fourth colors are provided with the input cutoff circuit. The circuit 10 and the input on / off circuit 50 are not provided.
Among the 24V power supply lines, the 24V power supply line for the drive circuit section is connected to the transistor Tr2 for turning on / off the transformer 25 of the power supply device 1 of the first color, and the power supply for the other colors (second to fourth colors). Connected to the device. Further, the 24V power supply line for the control circuit section and the clock signal are also connected to power supplies for other colors (second to fourth colors).
The input cutoff circuit 10 shown in FIG. 5 provided in the power supply device for the first color is turned on / off by the input on / off circuit 50 so that the power supply to the power supply devices of other colors is also turned on in synchronization with this. Repeat with off.

A third embodiment of the present invention will be described with reference to the accompanying drawings.
In the first embodiment described above, control is performed so that the power supply to the transformer 25 is intermittently operated when an abnormality occurs in the apparatus.
In this embodiment, the AC on / off variable signal is turned on / off by the input cutoff circuit 10 as shown in FIG.
The signal line of the AC on / off variable signal is connected to the transistor Tr1 of the input cutoff circuit 10, and the AC on / off variable signal output to the D / A conversion / PWM converter 22 is turned on / off.
Further, as shown in FIG. 8, the input cut-off circuit 10 can be configured to turn on and off the clock signal.
The signal line of the clock signal is connected to the transistor Tr1 of the input cutoff circuit 10, and the clock signal output to the sine wave generation circuit 20 is turned on / off.

A fourth embodiment of the present invention will be described with reference to the accompanying drawings.
In the present embodiment, as shown in FIG. 9, a current detection circuit 100 that detects a DC current on the secondary winding side of the transformer 60 is provided in the DC output circuit unit, and the detected current value of the current detection circuit 100 is expressed as MPU ( (Microprocessor unit) 300. The MPU 300 turns on and off the 24V power supply of the 24V power supply line based on the detected current value of the current detection circuit 100. By turning on / off the 24V power supply, the output of the alternating current is also controlled to be turned on / off as in the first embodiment.

A fifth embodiment of the present invention will be described with reference to the accompanying drawings.
In this embodiment, a timer IC 200 is provided in place of the input on / off circuit 50 as shown in FIG.
The timer IC 200 changes the on time and the off time of the input cutoff circuit 10 according to the determination result of the frequency determination circuit 55.
FIG. 11 shows an example of the connection configuration of the timer IC 200. By setting the resistance RA shown in FIG. 11 to 150 (kΩ), the resistance RB to 3.3 (kΩ), and the capacitor to 47 (μF), the on-time is about 4.99 sec and the off-time is about 0.10 sec. Can be set. Further, by setting the resistance RA shown in FIG. 11 to 300 (kΩ), the resistance RB to 3.3 (kΩ), and the capacitor to 47 (μF), the on-time is about 9.87 sec and the off-time is about 0.00. It can be set to 10 sec.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

It is a figure which shows the connection structure of the charging roller and the power supply which charges this charging roller. It is a figure which shows the structure of the power supply device of Example 1. FIG. The overall configuration of the power supply device and the wiring structure of the power supply line are shown. It is a timing chart which shows the operation timing of a power unit. It is a figure which shows the structure of the power supply device of Example 2, Comprising: It is a figure which shows the structure of the power supply device for 1st colors. It is a figure which shows the structure of the power supply device of Example 2, Comprising: It is a figure which shows the structure of the power supply apparatus for 2nd-4th colors. It is a figure which shows the structure of the power supply device of Example 3, and is a figure which shows the structure which turns on and off an AC ON / OFF variable signal by an input interruption circuit. It is a figure which shows the structure of the power supply device of Example 3, and is a figure which shows the structure which turns on and off a clock signal with an input cutoff circuit. It is a figure which shows the structure of the power supply device of Example 4, and is a figure which shows the structure which monitors DC output. It is a figure which shows the structure of the power supply device of Example 5, and is a figure which shows the structure which sets on / off of an input interruption circuit by timer IC. It is a figure which shows the connection structure of timer IC.

Explanation of symbols

1 Power supply (charging power supply)
10 Input cutoff circuit (input cutoff circuit, control signal cutoff circuit)
20 Sine Wave Generation Circuit 21 Constant Current Control Circuit 22 D / A Conversion / PWM Conversion Circuit 23 Constant Voltage Control Circuit (Control Circuit)
25, 60 Transformer 30 Current detection circuit 40 Voltage detection circuit (detection circuit)
50 Input on / off circuit (selection circuit)
55 Frequency judgment circuit (selection circuit)
61 drive circuit 62 constant voltage control circuit 65 voltage detection circuit 100 current detection circuit 200 timer IC
300 MPU

Claims (11)

A power supply device used for a charger of an image forming apparatus,
A charging power supply that superimposes a constant voltage DC output on a constant current AC output and supplies it to the charger;
A detection circuit for detecting a load abnormality of the charging power supply;
A control circuit for controlling the charging power supply so that the AC output supplied to the charger becomes a constant voltage;
An input cut-off circuit for cutting off the input of the charging power supply,
A power supply apparatus, wherein when a load abnormality is detected by the detection circuit, control is performed such that an alternating current output supplied to the charger is a constant voltage intermittent output by the control circuit and the input cutoff circuit.   2. The power supply apparatus according to claim 1, further comprising a selection unit that selects a cycle in which the input cutoff circuit is turned on and off according to a frequency of an input signal that determines a frequency of the constant current AC output.   The power supply apparatus according to claim 1, wherein the input cut-off circuit turns on and off the input of the charging power supply based on a detection voltage of the constant current AC output. The input cutoff circuit, the power supply device of any one of claims 1, characterized in that is provided in common to a plurality of charging power supply 3. A detection circuit for detecting a current of the constant voltage DC output;
On the basis of the detected current of the detection circuit, a power supply apparatus according to any one claim of 4 claims 1, characterized in that it comprises a control means for controlling the period for turning on and off of the input cutoff circuit. A power supply device used for a charger of an image forming apparatus,
A charging power supply that superimposes a constant voltage DC output on a constant current AC output and supplies it to the charger;
A detection circuit for detecting a load abnormality of the charging power supply;
A control circuit for controlling the charging power supply so that the AC output supplied to the charger becomes a constant voltage;
A control signal cut-off circuit for cutting off the control signal of the charging power supply,
A power supply apparatus, wherein when a load abnormality is detected by the detection circuit, an AC output supplied to the charger is controlled by a constant voltage intermittent output by the control circuit and the control signal cutoff circuit. The power supply apparatus according to claim 6 , further comprising a selection unit that selects a cycle in which the control signal cutoff circuit is turned on and off according to a frequency of the control signal. The power supply device according to claim 6 or 7, wherein the control signal cutoff circuit turns on and off the control signal based on a detection voltage of the constant current AC output. 9. The power supply device according to claim 6 , wherein the control signal cutoff circuit is provided in common for a plurality of charging power sources. A detection circuit for detecting a current of the constant voltage DC output;
10. The power supply device according to claim 6 , further comprising a control unit that controls a cycle of turning on and off the control signal cutoff circuit based on a detection current of the detection circuit. 11. The power supply device according to any one of claims 1 to 10,
An image forming apparatus comprising: a charging device that is charged by a power source supplied from the power source device and charges an image carrier.

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