JP2000014141A - Power supply device for image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power device for image forming apparatus capable of stabilizing its output voltage well at the time of driving an image forming means, and capable of increasing an overall power supply efficiency well. SOLUTION: An output voltage detecting and controlling circuit 137 performs control to turn a main switching element 117 off through an oscillation control circuit if the output voltage of a rectifying smoothing circuit 131 becomes higher than 24 V, and turns the main switching element 117 on if the output voltage becomes lower than 24 V. Consequently, the output voltage of the rectifying smoothing circuit 131 vibrates around 24 V. At a sleeping time of a printer, an output voltage sensitivity adjusting varying circuit 150 lowers the sensitivity of the output voltage detecting and controlling circuit 137, and makes the amplitude of the output voltage larger. As the result of this, a switching loss by the main switching element 117 decreases, and a power supply efficiency increases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for an image forming apparatus for supplying power to the image forming apparatus, and more particularly to a power supply for an image forming apparatus capable of outputting a DC voltage corresponding to a target value. .

[0002]

2. Description of the Related Art Conventionally, various DC actuators such as a DC motor have been used in an image forming apparatus provided with an image forming means for forming an image on a recording medium. on the other hand,
Image forming apparatuses such as printers often use an AC power supply as a main power supply. Therefore, various power supply devices for an image forming apparatus that rectify a voltage supplied from an AC power supply and output a DC voltage having a desired voltage corresponding to the capacity of the DC actuator have been proposed.

For example, a first rectifier circuit for rectifying a voltage supplied from an AC power supply, a switching circuit for switching a voltage rectified by the first rectifier circuit, and a current supplied to the primary side by the switching circuit. With a transformer
A second rectifier circuit for rectifying a voltage generated on a secondary side of the transformer and supplying the rectified voltage to at least the image forming means;
The switching circuit is turned off after the output voltage of the rectifier circuit exceeds the target value, and the switching circuit is turned on after the output voltage of the second rectifier circuit drops below the target value.
And a switching control unit that performs the switching.

In such a power supply device, the first rectifier circuit rectifies the voltage supplied from the AC power supply, and the switching circuit switches the rectified voltage. When a current flowing by this switching is applied to the primary side of the transformer to generate a voltage on the secondary side, the second rectifier circuit rectifies this voltage and outputs it as a DC voltage. This DC voltage is supplied to the image forming means, and this voltage is controlled by the switching control means as follows. That is, the switching control means turns off the switching circuit after the output voltage of the second rectifier circuit exceeds the target value, and turns on the switching circuit after the output voltage of the second rectifier circuit falls below the target value. For this reason, the output voltage of the second rectifier circuit oscillates around the target value. Further, if the ON / OFF of the switching circuit by the switching control means is repeated finely, the output voltage is stably controlled near the target value, and the DC actuator and the like can be driven more favorably.

[0005]

However, some image forming apparatuses have a sleep mode, which is a control mode in which the main power is turned on but the image forming means is not driven. In these control modes, the actuator such as the motor for driving the image forming unit does not operate, so that the output voltage of the second rectifier circuit is increased if the output voltage of the logic power supply for supplying power to the control unit is stable. There is little need to stabilize the accuracy. Therefore, when the ON / OFF of the switching circuit is finely repeated in the sleep mode as described above, the power consumption increases due to the switching loss while the current consumption on the secondary side is small. Further, even in an image forming apparatus having no sleep mode, there is little need to stabilize the output voltage when the image forming unit is hardly driven. However, in the conventional power supply device for an image forming apparatus, the output voltage is always stabilized so as to be able to cope with the driving of the image forming unit, so that the power supply efficiency as a whole is deteriorated.

Therefore, according to the present invention, the output voltage can be satisfactorily stabilized when the image forming means is driven.
It is an object of the present invention to provide a power supply device for an image forming apparatus that can improve the power supply efficiency as a whole.

[0007]

Means for Solving the Problems and Effects of the Invention The invention according to claim 1 for achieving the above object is used for an image forming apparatus provided with image forming means for forming an image on a recording medium, A first rectifier circuit for rectifying the voltage supplied from the AC power supply, a switching circuit for switching the voltage rectified by the first rectifier circuit, a transformer for supplying a current to the primary side by the switching circuit, A second rectifier circuit for rectifying the voltage generated on the secondary side of the second rectifier circuit and supplying the rectified voltage to at least the image forming means; and turning off the switching circuit after the output voltage of the second rectifier circuit exceeds a target value. A switching control unit for turning on the switching circuit after an output voltage of the rectifier circuit falls below the target value. By adjusting the timing at which the switching control circuit turns ON / OFF the switching circuit, when the current consumption in the second rectifier circuit is small, the amplitude of the output voltage of the second rectifier circuit is increased, and the current consumption is large. It is characterized by comprising amplitude control means for making it larger than usual.

According to the present invention, the amplitude control means adjusts the ON / OFF timing of the switching circuit by the switching control means, so that when the current consumption in the second rectifier circuit is small, the amplitude control means controls the second control circuit.
The amplitude of the output voltage of the rectifier circuit is made larger than when the current consumption is large. When the current consumption in the second rectifier circuit is small, the sleep mode described above is one mode, but there is little need to stabilize the output voltage of the second rectifier circuit. Therefore, in such a case, the amplitude of the output voltage of the second rectifier circuit is made larger than when the current consumption is large (for example, when the image forming unit is driven). By doing so, the number of times the switching circuit is repeatedly turned ON / OFF can be reduced, and the switching loss can be reduced to improve the power supply efficiency. Further, when the current consumption of the second rectifier circuit is large, such as when the image forming unit is driven, the amplitude of the output voltage can be reduced to stabilize. Therefore, according to the present invention, the output voltage can be satisfactorily stabilized when the image forming means is driven, and the power efficiency as a whole can be improved satisfactorily.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the image forming apparatus drives the image forming means in a control mode at least while the main power of the image forming apparatus is turned on. Not sleep mode,
An image forming mode for actually driving the image forming means to form an image, wherein the amplitude control means, when the sleep mode is set as the control mode,
The amplitude of the output voltage is made larger than when the image forming mode is set as the control mode.

According to the present invention, the image forming apparatus includes at least a sleep mode in which the main power of the image forming apparatus is turned on but the image forming means is not driven as the control mode, and an image which is actually driven by the image forming means. An image forming mode to be formed, and the amplitude control means controls the amplitude of the output voltage according to which control mode is set. For this reason, when it is desired to stabilize the output voltage, the output voltage can be reliably stabilized, and when the switching loss can be reduced, the output voltage can be significantly reduced.

Therefore, according to the present invention, in addition to the effects of the first aspect of the present invention, there is an effect that the image can be formed more favorably and the power supply efficiency can be further improved. The invention according to claim 3 is the invention according to claim 1 or 2
In addition to the configuration described above, further comprising a current consumption detecting means for detecting a current consumption in the second rectifier circuit, wherein the amplitude control means detects that the current consumption detected by the current consumption detecting means is small. It is characterized in that the amplitude of the output voltage is made larger than when the current consumption detected by the current consumption detecting means is large.

In the present invention, the current consumption in the second rectifier circuit is detected by the current consumption detecting means, and the amplitude control means controls the amplitude of the output voltage according to the current consumption. For this reason, the switching loss can be reduced according to the necessity of stabilizing the output voltage actually. For example, even if the image forming mode is set,
Actually, when the image forming unit is hardly driven, the amplitude of the output voltage is increased to reduce the switching loss and to improve the power supply efficiency.

Therefore, according to the present invention, in addition to the effect of the first or second aspect of the present invention, an effect that the power supply efficiency can be further improved can be obtained. According to a fourth aspect of the present invention, in addition to the configuration according to any one of the first to third aspects, the amplitude control means transmits a change in the output voltage of the second rectifier circuit to the switching control means with a delay. Thus, the amplitude of the output voltage is increased.

If the fluctuation of the output voltage of the second rectifier circuit is transmitted to the switching control means with a delay, the amplitude of the output voltage can be changed even if the switching control means normally performs the operation of turning on or off the switching circuit. Becomes larger. In the present invention, since the amplitude is increased by the amplitude control means transmitting the fluctuation of the output voltage to the switching control means with a delay, there is no need to change the configuration of the switching control means at all. Further, the configuration of the amplitude control means for transmitting the fluctuation of the output voltage with a delay can be easily realized by a simple circuit using a well-known integrating circuit or the like.

Therefore, according to the present invention, in addition to the effect of any one of the first to third aspects of the present invention, an effect that the configuration of the apparatus can be further simplified is produced.

[0016]

Next, an embodiment of the present invention will be described. FIG. 1 is a perspective view of main components of a laser printer as an image forming apparatus to which the present invention is applied, and FIG. 2 is a schematic sectional side view of the laser printer.

As shown in FIG. 1, a main body case 1 made of synthetic resin in a laser printer has a main frame 1a.
And a main cover 1b that covers the outer surface of the main frame 1a on four sides (front and rear and left and right sides). The main frame 1a and the main cover 1b are integrally formed by injection molding or the like.

A scanner unit 2 as an exposure unit, a process unit 3 as an image forming unit, a fixing unit 4 as a fixing unit, and a sheet feeding unit 5 are mounted on the main frame 1a from the top. The drive system unit 6 including the main motor 84 (see FIG. 3) and the gear train is located in the storage recess 1d between the left inner surface of the main cover 1b in FIG. 1 and the left side of the main frame 1a adjacent thereto. It is inserted and fixed from below the main body case 1. Further, a top cover 7 serving as a main body cover made of synthetic resin for covering the upper surfaces of the main frame 1a and the main cover body 1b has a hole 7a through which an operation panel 1c projecting upward to the right side of the main frame 1a.
And a hole 7b for penetrating the base of the sheet feeding unit 5. The base of the paper discharge tray 8 is attached to brackets 9 (only one is shown in FIG. 1) protruding from the left and right sides of the front end of the top cover 7 so as to be vertically swingable. 8 can be folded and covered on the upper surface side of the top cover 7.

In the feeder unit case 5a of the paper feed unit 5, recording papers P as recording media are set in a stacked state. As shown in FIG. 2, the leading end side of the recording paper P is pressed toward the paper feed roller 11 by a support plate 10 urged by a spring 10a in the feeder case 5a. Therefore, the recording paper P can be separated one by one and sent to the pair of upper and lower registration rollers 13 and 14 by the paper feed roller 11 and the separation pad 12 which are rotated by the power transmitted from the drive system unit 6. .

The process unit 3 includes a registration roller 1
An image is formed on the surface of the separated recording paper P fed by 3 and 14 using toner as a recording material. Further, the fixing unit 4 heats the recording paper P on which the toner image is formed by sandwiching the recording paper P between the heating roller 15 and the pressing roller 16 to fix the toner image on the recording paper P.
The heating roller 15 includes a fixing heater 15 made of a halogen lamp in a fluorine-coated aluminum tube.
The thermistor 107 is in contact with the outer surface at a substantially central portion in the longitudinal direction. The pressing roller 16 is a rubber roller whose surface is covered with a fluororesin.

A paper discharge unit including a paper discharge roller 17 and a pinch roller 18 disposed downstream in the case of the fixing unit 4 discharges the recording paper P on which the toner image has been fixed to a paper discharge tray 8. The section from the paper feed roller 11 to the paper discharge section is a recording medium transport route. The paper feed unit 5 is provided with a manual insertion opening 5b that opens diagonally upward, and the recording paper for printing on a recording paper different from the recording paper P in the feeder case 5a is used for the recording. It can be inserted into the medium transport route.

An upper support plate 2a of the scanner unit 2 has a bottom plate of the main frame 1a at a position below the process unit 3 which is disposed substantially at the center of the main frame 1a having a top open box shape in the main body case 1 in plan view. It is fixed to a stay part integrally formed on the upper surface side of the part with screws or the like.
In the scanner unit 2 as an exposure unit, a laser light emitting unit (not shown), a polygon mirror 20, a lens 21, a reflecting mirror 22, and the like are arranged on the lower surface side of the synthetic resin upper support plate 2a. . This scanner unit 2
Irradiates the outer peripheral surface of the photosensitive drum 23 with a laser beam through a glass plate 24 covering a horizontally elongated scanner hole formed in the upper support plate 2a so as to extend along the axis of the photosensitive drum 23 as a photosensitive member. And is exposed.

As shown in FIG. 2, the process unit 3
Is a photosensitive drum 23 and a transfer roller 2 in contact with the upper surface thereof.
5, a scorotron-type charger 26 disposed below the photosensitive drum 23, a developing device having a developing roller 27 and a supply roller 28 disposed upstream of the photosensitive drum 23 in the sheet feeding direction, and further disposed upstream thereof Developer (toner) supply unit, ie, detachable toner cartridge 2
9, a cleaning roller 30 disposed downstream of the photosensitive drum 23, and a discharge lamp 30a disposed downstream of the cleaning roller 30.

A charger 26 is provided on the outer peripheral surface of the photosensitive drum 23.
An electrostatic latent image is formed by scanning a laser beam from the scanner unit 2 on the charged photosensitive layer. Developer (toner) in the toner cartridge 29
Is released by being stirred by the stirrer 31 and then carried on the outer peripheral surface of the developing roller 27 via the supply roller 28, and the thickness of the toner layer is regulated by the blade 32. The electrostatic latent image on the photosensitive drum 23 is visualized by the developer adhering from the developing roller 27. The image (toner image) of the developer is transferred to the recording paper P passing between the transfer roller 25 and the photosensitive drum 23 to which a transfer bias having a potential opposite to the potential of the photosensitive drum 23 is applied to form a toner image. I do. Then, the toner remaining on the photosensitive drum 23 is temporarily collected by the cleaning roller 30 and then returned to the photosensitive drum 23 at a predetermined timing, and
7 collects in the process unit 3.

The upper support plate 2a of the scanner unit 2
Is provided with a toner sensor 33 protruding upward, and a toner sensor 33 composed of a pair of a light emitting unit and a light receiving unit faces the lower surface recess of the toner cartridge 29 in the process unit 3, and the presence or absence of toner in the toner cartridge 29. Can be detected.

The process unit 3 is made into a cartridge by being incorporated in a case 34 made of synthetic resin.
The process unit 3 formed into a cartridge is detachably mounted on the main frame 1a. A storage portion 3 for storing the cooling fan 35 is provided on the lower surface side of the continuous portion between the front portion of the main frame 1a and the front portion of the main cover body 1b.
6 and a ventilation duct 37 extending in the left-right direction perpendicular to the direction in which the recording paper P passes, are formed to communicate with each other. Then, the upper surface plate portion 37a of the ventilation duct 37 is formed in a V-shape with a downward section, and the upper surface plate portion 37a is located between the process unit 3 and the fixing unit 4 to generate the heat generated by the heating roller 15 in the fixing unit 4. To prevent the heat generated from directly transmitting to the process unit 3 side.

The cooling air generated by the cooling fan 35 passes through the inside of the ventilation duct 37 and along the lower surface of one side of the main frame 1a.
While cooling the main motor 84, the cooling air blows out from a plurality of slit holes opened on the process unit 3 side in the upper surface plate portion 37a, and the cooling air passes between the process unit 3 and the fixing unit 4 and rises. And top cover 7
The gas is discharged out of the device through the exhaust holes 40 formed in a plurality of holes.

Next, the control unit 70 provided inside the right side of the main frame 1a will be described. FIG.
3 is a block diagram showing the control unit 70 and a configuration related to the control unit 70. FIG. The control unit 70
CPU 71 and RO storing various control programs
M72, a RAM 73 provided with various memories such as a reception buffer for receiving and storing transmission data transmitted from an external data transmission device PC such as a personal computer or a host computer, and timing for writing / reading reception data to / from the reception buffer Control circuit (TC) 74 for generating a timing signal for printing, and an interface (I / F) 7 for receiving transmitted print data.
5, a video interface (V.I / F) 76 having a scan buffer and sequentially outputting print information converted to bit image data to the DC controller circuit 82
And a sensor interface (S · I) that receives detection signals from the toner sensor 33, the paper feed sensor 51 provided in the vicinity of the downstream of the paper feed roller 11, and other sensors.
/ F) 77 and a panel interface (P / I / F) 78 for selecting various control modes from the operation panel 1c and receiving the switched signal. These are connected to the CPU 71 via the bus 81, respectively. Have been.

The DC controller circuit 82 includes a paper-feeding-side transport mechanism including the paper-supplying roller 11, registration rollers 13 and 14, the photosensitive drum 23, and the like. And pinch roller 18
Motor 8 for driving the discharge-side transport mechanism section comprising
4, a drive circuit 89 for a laser diode 85 constituting the laser emitting section, a drive circuit 90 for a scanner motor 86 for driving the polygon mirror 20, and a halogen circuit in the heating roller 15. A driving circuit 91 as a fixing unit driving circuit for the fixing heater 15a composed of a lamp, the photosensitive drum 23, and the transfer roller 2;
5, a high-voltage substrate 92 that generates a high-voltage electric field in the charger 26, the developing roller 27, and the cleaning roller 30, and further turns on the static elimination lamp 30a is connected to each other.

In the ROM 72, in addition to various control programs as a normal laser printer and a program of a flowchart described later, a font memory storing printing dot pattern data relating to a large number of characters such as characters and symbols, a RAM 73 A memory management program that manages the memory capacity and the start address of each memory such as a reception data buffer and a print image memory provided in advance is stored in advance.

Next, the configuration of the drive circuit 91 and its peripherals will be described in detail with reference to FIG. As shown in FIG. 4, the drive circuit 91 is mainly composed of various elements such as a triac 93 b and a triac 95 of the phototriac coupler 93, and various resistors and capacitors described below. At both ends of the triac 93b,
Triac 9 via resistors 97a and 97b respectively
5 are connected at both ends. The gate of the triac 95 is connected between the resistor 97a and the triac 93b, and a capacitor 99 is connected to the gate in parallel with the resistor 97a. For this reason, when the triac 93b is turned on and a current flows through the resistor 97a, a gate current corresponding to the voltage drop is supplied.

Between both ends of the triac 95, AC1
00V commercial power supply 101, power switch 103, fuse 105 that blows when a current greater than or equal to a predetermined value flows, fixing heater 15a, and temperature at which fuser 15a blows when it becomes abnormally high. Fuse 15b
Are connected in series. Further, a DC power supply circuit 110 that outputs DC voltages of 5 V and 24 V, which will be described later, is connected to both ends of a series circuit including the commercial power supply 101, the power switch 103, and the fuse 105.

One end of the thermistor 107 in contact with the surface of the heating roller 15 is grounded via a resistor 109 and the other end is connected to a DC power supply of 5 V.
7, the potential between the resistors 109 is input to the CPU 71 via an A / D converter (not shown). Therefore, CPU
Reference numeral 71 denotes a heating roller 1 by reading the potential.
5 can be detected. Also, the CPU 7
1 is also connected to the light emitting diode 93a of the phototriac coupler 93 so as to be able to output.

Therefore, the CPU 71 sets the thermistor 107
The ON / OFF of the phototriac coupler 93 is switched based on the surface temperature detected through the control circuit, and the energization / non-energization of the fixing heater 15a is switched as follows. That is, when the power switch 103 is ON and the light emitting diode 93a emits light, the triac 93b is turned off.
Then, a current flows through the parallel circuit of the resistor 97a and the capacitor 99, and the triac 95 is turned on. For this reason, the ON / OFF of the phototriac coupler 93 coincides with the ON / OFF of the triac 95, whereby the energization / non-energization of the fixing heater 15a is switched. Since the triac 95 is turned off, the zero cross operation is performed.
F. Further, when the phototriac coupler 93 has the zero cross detection, the ON of the triac 95 is turned on at a maximum delay of a half cycle of the power supply frequency from the ON of the triac 93b.

Next, the configuration of the DC power supply circuit 110 as a power supply for an image apparatus will be described. Commercial power supply 101
Is input through the power switch 103 and the fuse 105 to be rectified through the input filter circuit 111 and the rectifying / smoothing circuit 113 as the first rectifying circuit. The DC voltage output from the rectifying / smoothing circuit 113 is applied to a main switching element 11 as a switching circuit whose ON / OFF is switched by an oscillation control circuit 115.
7 (configured with FETs in this example) and the transformer 1
21 and a coil 123 on the primary side. The oscillation control circuit 115 is a self-excited circuit having a coil 115a in a transformer 121. The oscillation control circuit 115 turns on / off the main switching element 117.
By switching F, the current flowing through the coil 123 is switched.

The voltage generated in the coil 125 on the secondary side of the transformer 121 by the application of this current is rectified by a rectifying / smoothing circuit 131 as a second rectifying circuit, and the voltage is reduced to 24 V.
Is supplied to the main motor 84 and the like. The 24 V DC voltage is supplied to the DC-DC converter 1.
The voltage is converted to a DC voltage of 5 V via the 33 and the smoothing circuit 135 and supplied as a reference voltage of the control unit 70 and the like.

The DC power supply circuit 110 further includes an output voltage detection control circuit 137 as switching control means and an output voltage sensitivity adjustment variable circuit 150 as amplitude control means. The output voltage of the rectifying / smoothing circuit 131 is input to the output voltage detection control circuit 137. The output voltage detection control circuit 137 is connected to the phototransistor coupler 1
A control signal is input to the oscillation control circuit 115 via 39,
The OFF period of the main switching element 117 controlled by the oscillation control circuit 115 is defined so that the rectifying and smoothing circuit 131 stably outputs a DC current of 24 V.

That is, when the output voltage of the rectifying / smoothing circuit 131 exceeds 24 V, the main switching element 117 is controlled to be turned off via the oscillation control circuit 115, and when the output voltage falls below 24 V, the main switching element 117 is controlled via the oscillation control circuit 115. To control the main switching element 117 to be ON. The oscillation control circuit 115 controls the main switching element 117 to be turned on after detecting the disappearance of the magnetic flux in the transformer 121. However, the output voltage detection control circuit 137 normally operates at substantially the same timing as the disappearance of the magnetic flux in the transformer 121. A control signal for turning on the switching element 117 is output. As a result, the output voltage of the rectifying / smoothing circuit 131 becomes 24
Vibration about V occurs.

The output voltage sensitivity adjustment variable circuit 150
Adjusts the sensitivity of the output voltage detection control circuit 137 based on the control signal input from the CPU 71. That is,
If the sensitivity of the output voltage detection control circuit 137 is reduced so that the output voltage of the rectifying / smoothing circuit 131 exceeds or drops below 24 V with a delay, the output voltage detection control circuit 137 becomes main. Switching element 1
The timing of controlling the switch 17 to OFF or ON is delayed. As a result, the amplitude of the output voltage increases.

Subsequently, the output voltage detection control circuit 137
And the configuration of the output voltage sensitivity adjustment variable circuit 150,
This will be described in detail with reference to FIG. First, the output voltage detection control circuit 137 controls the shunt regulator 14 in which the output voltage of the rectifying and smoothing circuit 131 divided by the resistor 141, the variable resistor 142, and the resistor 143 is input to the gate.
5 is provided. The shunt regulator 145 has an anode grounded and a cathode connected to the resistor 147 and the light emitting diode 139 a of the phototransistor coupler 139.
And the output voltage of the rectifying / smoothing circuit 131 is input through the terminal. Also, the cathode of the shunt regulator 145
An output stabilizing resistor 148 and a capacitor 149 are connected between the gates.

The shunt regulator 145 has a reference voltage corresponding to when the output voltage of the rectifying / smoothing circuit 131 becomes 24 V. When the output voltage exceeds 24 V, the shunt regulator 145 conducts and turns on the light emitting diode 139a. Let it. In response, when the transistor 139b of the phototransistor coupler 139 turns on, the oscillation control circuit 115
Controls the main switching element 117 to be OFF.
When the output voltage falls below 24 V and the shunt regulator 145 stops conducting, the transistor 139
b turns off, and the oscillation control circuit 115 turns on the main switching element 117 after the magnetic flux in the transformer 121 disappears (usually immediately).

On the other hand, the output voltage sensitivity adjustment variable circuit 150
Includes a circuit for grounding the gate of the shunt regulator 145 via the capacitor 151 and the transistor 153. A resistor 155 is connected between the base and the emitter of the transistor 153, the emitter is grounded, and the base is connected to a 5V DC power supply via the resistors 157 and 159. Therefore, the resistor 157,
By inputting a control signal from the CPU 71 during 159, ON / OFF of the transistor 153 is switched. Therefore, if the transistor 153 is turned on by a control signal from the CPU 71, the shunt regulator 145
The variation of the gate voltage causes a delay according to the capacitance of the capacitor 151. With this operation, the shunt regulator 145 and, consequently, the output voltage detection control circuit 13
7, the sensitivity to the output voltage of the rectifying / smoothing circuit 131 can be reduced.

Therefore, the CPU 71 switches the sensitivity as follows. First, the CPU 71 has the following sleep mode and standby mode as control modes in addition to the image forming mode in which the process unit 3 is actually driven to actually form an image. Sleep mode refers to CP
U71 reads a signal from the operation panel 1c and also drives the DC power supply circuit 110, but the drive circuits 87 to 91,
Alternatively, this is a processing mode in which energization to each unit via the high-voltage board 92 is completely interrupted. The standby mode is a processing mode in which the fixing heater 15a is kept warm in preparation for image formation, and is the same as the above-described image forming mode except that the temperature of the fixing heater 15a is slightly lower. The CPU 71 determines whether to take the processing mode of the sleep mode, the standby mode, or the image forming mode based on a signal from the operation panel 1c and the driving state of the process unit 3 by software (determining means) processing. I do.

FIG. 6 shows a mode switching process when the CPU 71 automatically switches the mode.
This will be described with reference to the flowchart of FIG. Note that the CPU 71
Executes this process as an interrupt process at a predetermined interval after the power is turned on. As shown in FIG. 6, when the power is turned on, S1
(S represents a step: the same applies hereinafter), the standby mode is set, and the timer is started in subsequent S2. In the standby mode, the CPU 71 turns off the transistor 153.
And the sensitivity of the output voltage detection control circuit 137 is set to the normal sensitivity.

Subsequently, it is determined whether or not data has been received in S3, and if not (S3: NO), it is determined whether or not the operation panel 1c has been operated (S4). If the operation panel 1c has not been operated (S4: NO), it is determined whether or not a predetermined time has elapsed from the timer start (S2) (S5). If not (S5: NO), the above-described S3 is not performed. If the time has elapsed (S5: YES), S
After setting the sleep mode at 6, the process proceeds to S3. That is, when the power is turned on, the standby mode is set once (S1), and when the predetermined time has elapsed (S3: S4: NO) without receiving data or operating the operation panel 1c (S5: YES), the standby mode is set. To sleep mode. In the sleep mode, the transistor 153 is turned on, and the output voltage detection control circuit 1
Set the sensitivity of 37 to low sensitivity.

When data is received (S3: YE
S) and when the operation panel 1c is operated (S4:
YES) goes to S7 to set the image forming mode,
The process waits until the image forming process by another routine is completed (S8). When shifting to the image forming mode,
By controlling the transistor 153 to be OFF, the sensitivity is set to the normal sensitivity. When the image forming process is completed (S8: Y
ES) The process shifts to S1, sets the standby mode, and repeats the above-described processing. When the predetermined time has elapsed again without receiving data or operating the operation panel 1c (S5: YES), the mode is switched to the sleep mode and the sensitivity is set to low sensitivity.

As described above, in the sleep mode, the current supply to the respective components via the driving circuits 87 to 91 or the high voltage substrate 92 is completely interrupted, so that the output voltage (24 V) of the rectifying / smoothing circuit 131 is stabilized. There is little need. Therefore, in the DC power supply circuit 110, when the sleep mode is set, the sensitivity of the output voltage detection control circuit 137 is set to low sensitivity, and the amplitude of the output voltage is increased. By doing so, the main switching element 11
7, the number of times that ON / OFF is switched can be reduced, switching loss can be reduced, and power supply efficiency can be improved.

In the image forming mode in which the process unit 3 is driven to form an image, the sensitivity of the output voltage detection control circuit 137 is set to the normal sensitivity, and the rectifying / smoothing circuit 131 is set.
Can be stabilized by reducing the amplitude of the output voltage. Therefore, the main motor 84 and the like are driven stably,
A good image can be formed. Therefore, in the present embodiment, the output voltage can be satisfactorily stabilized when the process unit 3 is driven, and the power supply efficiency as a whole can be improved satisfactorily. Moreover,
Since the sensitivity is set according to the control mode of the CPU 71, the output voltage can be reliably stabilized when it is desired to stabilize the output voltage, and can be significantly reduced when the switching loss can be reduced. Therefore, in the present invention, the image formation can be performed more favorably, and the power supply efficiency can be further improved.

FIG. 7 is a circuit diagram showing another form of the DC power supply circuit 110. In this DC power supply circuit 110,
A resistor 169 is connected in series to the output side of the rectifying / smoothing circuit 131, and a current amount as current consumption detecting means for detecting the consumption of the current output from the rectifying / smoothing circuit 131 based on the voltage drop by the resistor 169. A detection circuit 170 is provided. In the DC power supply circuit 110, based on the current consumption detected by the current detection circuit 170, when the current consumption is large, the output voltage sensitivity adjustment variable circuit 1
The sensitivity defined by 50 is set to normal sensitivity, and when the current consumption is small, the sensitivity is set to low sensitivity.

In the present embodiment configured as described above,
Switching loss can be reduced according to the necessity of stabilization of the output voltage in practice (the higher the current consumption, the higher the necessity of stabilization of the output voltage). For example,
Even if the image forming mode is set, the process unit 3 is hardly actually driven (a huge amount of time is required for data processing, and the corresponding process unit 3 is not driven).
In such a case, it is possible to increase the amplitude of the output voltage, reduce switching loss, and improve power supply efficiency. Therefore, in the present embodiment, the power supply efficiency can be further improved. Needless to say, the control of the sensitivity (amplitude of the output voltage) according to the control mode as described above may be combined with the control of the sensitivity (amplitude of the output voltage) according to the current consumption. Absent.

The present invention is not limited to the above embodiments, and can be implemented in various forms without departing from the gist of the present invention. For example, in each of the above embodiments, the sensitivity of the output voltage detection control circuit 137 is switched between the two levels of the normal sensitivity and the low sensitivity. However, the sensitivity may be switched in three or more levels, or continuously (in an analog manner). You may switch. Further, in each of the above embodiments, the shunt regulator 145 is provided with the rectifying and smoothing circuit 131.
The amplitude is increased by transmitting the fluctuation of the output voltage with a delay, but various forms are conceivable as amplitude control means for controlling the amplitude of the output voltage. For example,
The upper and lower limits of the amplitude may be controlled, and the upper and lower limits may be switched depending on the mode. However, the configuration of the amplitude control means for transmitting the fluctuation of the output voltage with a delay can be easily realized by a simple circuit using a well-known integration circuit or the like. Therefore, in each of the above embodiments, the configuration of the device can be further simplified. Further, the present invention is not limited to a laser printer, but can be applied to various image forming apparatuses such as a copying machine and an ink jet printer.

[Brief description of the drawings]

FIG. 1 is a perspective view of main components of a laser printer according to an embodiment.

FIG. 2 is a schematic side sectional view of the laser printer.

FIG. 3 is a block diagram illustrating a control unit of the laser printer and a configuration related to the control unit.

FIG. 4 is a circuit diagram illustrating a configuration of the drive circuit and the DC power supply circuit.

FIG. 5 is a circuit diagram showing a detailed configuration of the DC power supply circuit.

FIG. 6 is a flowchart illustrating a mode switching process of a control unit.

FIG. 7 is a circuit diagram illustrating another form of the DC power supply circuit.

[Explanation of symbols]

2. Scanner unit 3. Process unit
4: fixing unit 5: paper feeding unit 6: drive system unit 15
... Heating roller 70 ... Control unit 71 ... CPU 91 ... Drive circuit 101 ... Commercial power supply 110 ... DC power supply circuit 111
... input filter circuits 113,131 rectifying and smoothing circuit 115 ... oscillation control circuit 117 ... main switching element 121 ... transformers 123,125 ... coil 137 ... output voltage detection control circuit 150 ... output voltage sensitivity adjustment variable circuit 170 ... current amount detection circuit

Claims (4)

[Claims] A first rectifier circuit for rectifying a voltage supplied from an AC power supply, wherein the first rectifier circuit is used for an image forming apparatus having an image forming means for forming an image on a recording medium; A switching circuit for switching a voltage, a transformer in which a current is supplied to the primary side by the switching circuit, and a second rectifying circuit for rectifying a voltage generated on a secondary side of the transformer and supplying the rectified voltage to at least the image forming means Switching control means for turning off the switching circuit after the output voltage of the second rectifier circuit exceeds the target value, and turning on the switching circuit after the output voltage of the second rectifier circuit falls below the target value. A power supply device for an image forming apparatus, comprising:
By controlling the N / OFF timing, when the current consumption in the second rectifier circuit is small, the amplitude control that increases the amplitude of the output voltage of the second rectifier circuit as compared with when the current consumption is large. Power supply device for an image forming apparatus, comprising: 2. The image forming apparatus according to claim 1, wherein a control mode is a sleep mode in which a main power supply of the image forming apparatus is turned on but the image forming unit is not driven, and that the image forming unit is actually driven. An image forming mode for forming an image, wherein the amplitude control means sets the amplitude of the output voltage when the sleep mode is set as the control mode, and sets the image forming mode as the control mode. The power supply device for an image forming apparatus according to claim 1, wherein the power supply device is larger than when the power supply is in operation. 3. The apparatus according to claim 2, further comprising a current consumption detecting means for detecting a current consumption in the second rectifier circuit, wherein the amplitude control means detects the current consumption when the current consumption detected by the current consumption detecting means is small. 3. The power supply device for an image forming apparatus according to claim 1, wherein the amplitude of the output voltage is made larger than when the current consumption detected by said current consumption detecting means is large. 4. An apparatus according to claim 1, wherein said amplitude control means increases the amplitude of said output voltage by transmitting a change in output voltage of said second rectifier circuit to said switching control means with a delay. The power supply device for an image forming apparatus according to any one of claims 1 to 3.