JP2004187475A - Control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control system capable of stabilizing starting characteristics and eliminating power consumption by a dummy load after starting, and to provide a control method of the dummy load in an image forming apparatus and a multi-output power supply. <P>SOLUTION: When a multi-output power supply is started, a transistor 76 is turned on as a 24V output increases to connect a dummy load 23 with a 24V output end. When the load on the multi-output power supply is increased after starting, a transistor 79 is turned on by an output from a microcontroller 70. Consequently, the transistor 76 is turned off to disconnect the dummy load 23 from a rectifying/smoothing section. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control system including a multi-output power supply device that generates a plurality of DC outputs, and more particularly to connection of a dummy load at the time of transition from startup to a steady state.
[0002]
[Prior art]
A conventional multi-output power supply device will be described using a self-excited flyback converter (RCC: ringing choke converter) shown in FIG. 10 as a basic circuit. The insulating transformer 1 includes an input-side primary winding Np, an output-side secondary winding Ns1, Ns2, and a primary-side auxiliary winding Nb. The auxiliary winding Nb is a driving winding for the gate voltage control transistor 3 of the MOS-FET 2 which is a switching element. The input voltage E is a DC voltage obtained by rectifying an AC input voltage with a bridge diode and smoothing the input voltage with an AL electrolytic capacitor. The input voltage E is applied between one end of the primary winding Np and the source terminal of the MOS-FET 2, the (+) side of the input voltage starts to be wound around the primary winding Np, and the (-) side of the input voltage is It is connected to the source terminal of MOS-FET2. The auxiliary winding Nb is connected to the same polarity as the primary winding Np, and the secondary winding Ns is connected to the opposite polarity.
[0003]
Starting resistors 4 and 5 are connected between the input voltage E and the gate of the MOS-FET 2. A capacitor 6 and gate resistors 7 and 8 are connected between the gate of the MOS-FET 2 and the beginning of the auxiliary winding Nb. A diode 9 having the auxiliary winding Nb side facing the cathode is connected to both ends of the gate resistor 8, and the efficiency of turning on and off the MOS-FET 2 is adjusted to achieve high efficiency. A capacitor 10 is connected between the base of the transistor 3 and the (−) side of the input voltage. A resistor 11 is connected between the auxiliary winding Nb and the base of the transistor 3, and forms a time constant circuit with the capacitor 10. A resistor 13 is connected between the collector of the photocoupler 12 and the gate of the MOS-FET 2 to limit a current flowing through the photocoupler 12. The emitter of the photocoupler 12 is connected to the base of the transistor 3.
[0004]
At the end of the winding of the secondary windings Ns1 and Ns2 of the insulating transformer 1, the anode sides of the diodes 14 and 15 for rectification are connected. Electrolytic capacitors 16 and 17 are connected between the cathodes of the diodes 14 and 15 and the start of the winding of the secondary windings Ns1 and Ns2 to perform smoothing. The output voltage 24V is divided by the resistors 18 and 19, and the divided voltage is connected to the ref terminal of the shunt regulator 20, and controls the current flowing through the diode of the photocoupler 12 by comparing with the internal reference voltage. I have. A three-terminal regulator 21 is connected to the output side of the capacitor 16 and generates an output voltage of, for example, 5V. The capacitor 22 is an electrolytic capacitor connected to the output side of the three-terminal regulator 21. A resistor 23 is connected to the 24V output as a dummy load, so that the oscillation state of the MOS-FET 2 is intermittent, preventing the generation of an audible (20 kHz or less) oscillation sound from the insulating transformer 1 and intermittently. Since the start is repeated by the oscillation, the MOS-FET 2 is stressed, and the ripple component of the output voltage is prevented from increasing.
[0005]
Usually, the resistor 23 consumes about several watts of power. In the conventional example, a multi-output power supply having two 5V outputs for the control system circuit and two 24V outputs for the drive system circuit is described as an example.
[0006]
The bias is applied to the gate of the MOS-FET 2 by the starting resistors 4 and 5, and the MOS-FET 2 is turned on. When the MOS-FET 2 is turned on, the input voltage E is applied to the primary winding Np, and a voltage with a winding start side (+) is induced in the auxiliary winding Nb. At this time, although a voltage is induced also in the secondary windings Ns1 and Ns2, no voltage is transmitted to the secondary side since the voltage is set to the negative side of the rectifier diodes 14 and 15 (−). Therefore, the current flowing through the primary winding Np is only the exciting current of the insulating transformer 1, and energy proportional to the square of the exciting current is stored in the insulating transformer 1. This exciting current increases in proportion to time. The gate of the MOS-FET 2 is charged by the voltage induced in the auxiliary winding Nb via the capacitor 6 and the resistors 7 and 8, and the conduction state is continued. The resistor 11 and the capacitor 10 constituting the time constant circuit are charged with electric charge from the auxiliary winding Nb. When the voltage across the capacitor 10 becomes higher than Vbe of the transistor 3, the transistor 3 is turned on, and the MOS-FET 2 When the gate voltage decreases, the MOS-FET 2 is turned off. At this time, a voltage is generated in each winding of the insulating transformer 1 in a direction opposite to that at the time of starting, and a voltage is generated in the secondary winding with the anode sides of the rectifier diodes 14 and 15 being (+). Is rectified and smoothed and transmitted to the secondary side. When all the energy stored in the insulating transformer 1 is transmitted to the secondary side, the MOS-FET 2 becomes conductive again. This is because a voltage proportional to the voltage between the drain and source of the MOS-FET 2 is generated in the auxiliary winding NB, but the gate is biased to (-) immediately after the MOS-FET 2 is turned off. However, when the energy transfer to the secondary side ends, the bias of (−) gradually decreases, and the gate of the MOS-FET 2 is biased again in the (+) direction from the C-coupled capacitor 6. is there. Since a large amount of current flows from the photocoupler 12 when the output voltage 24V is high, the current is supplied to the capacitor 10 and the charging time is shortened. This indicates that the conduction time of the MOS-FET 2 is shortened. As a result, the energy stored in the insulating transformer 1 is reduced, so that the output voltage 24V is reduced and the constant voltage operation is performed. The reverse operation is performed when the output voltage is low.
[0007]
FIG. 11 shows waveforms at various parts in the RCC system. VG indicates the gate voltage of the MOS-FET 2, VDS indicates the drain-source voltage of the MOS-FET 2, ID indicates the drain current, and IS indicates the current flowing through the rectifier diode 15 on the secondary side. First, the ON period of the MOS-FET 2 will be described. The bias is applied to the gates by the starting resistors 4 and 5, and the potential of VG rises, so that the MOS-FET 2 becomes conductive, the ID increases linearly with a positive slope with time, and energy is accumulated in the insulating transformer 1. Is done. At this time, the potential of VDS is almost zero because the MOS-FET 2 is in a conductive state, and IS does not flow because the rectifier diode 14 on the secondary side is reverse-biased. When the capacitor 10 is charged and the transistor 3 becomes conductive, the gate voltage VG of the MOS-FET 2 becomes zero and the MOS-FET 2 becomes non-conductive, so that ID becomes zero, and VDS becomes the input voltage E and the secondary voltage. And a surge voltage superimposed on the output voltage on the side of the winding. At this time, the rectifier diode 14 on the secondary side becomes conductive, and the energy stored in the insulating transformer 1 is transmitted to the secondary side. IS decreases linearly with a negative slope.
[0008]
[Problems to be solved by the invention]
However, in the conventional configuration, a dummy resistor (hereinafter referred to as a dummy) provided to the DC output in order to stabilize the start-up characteristics, increase output ripple voltage due to intermittent oscillation, prevent stress on switching elements and the like, and prevent noise from the transformer. (Referred to as a load) must always be used as a load, and there has been a problem such as a rise in the temperature of peripheral components due to the constant heating of the dummy resistor. In addition, during the printing operation of a laser beam printer or the like, there is a problem such as an increase in input power because extra power is consumed by the dummy resistor.
[0009]
The present invention has been made under such a situation, and has a control system, an image forming apparatus, and a multi-output power supply device capable of stabilizing start-up characteristics and eliminating power consumption by a dummy load after start-up. It is an object of the present invention to provide a dummy load control method in the above.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, the control system is configured as in the following (1), (2), and (4), and the image forming apparatus is configured as in the following (3) and (5). The control method of the dummy load in the multiple output power supply device is configured as in the following (6).
[0011]
(1) A transformer having a primary winding and a plurality of secondary windings, a switching element connected between the primary winding of the transformer and a DC power supply for performing switching, and a secondary winding of the transformer A rectifying and smoothing unit for rectifying and smoothing the AC voltage generated in each of the above, a dummy load connected to the rectifying and smoothing unit, and a DC output of at least one of a plurality of DC outputs output from the rectifying and smoothing unit. A multi-output power supply device comprising: a control unit that controls the switching element according to the
A microcontroller powered by at least one or more of the plurality of DC outputs of the multiple output power supply;
DC output is supplied from the multi-output power supply device, a motor device controlled by the microcontroller,
In the control system composed of
The dummy load is connected to the rectifying and smoothing unit at the time of starting the multi-output power supply device, and when the load of the multi-output power supply device increases after the starting, the dummy load is separated from the rectifying and smoothing unit by the microcontroller. A control system characterized by the following.
[0012]
(2) In the control system according to (1),
A control system, wherein after the multi-output power supply is started, a drive current of the motor device is controlled by the microcontroller to increase a load of the multi-output power supply and substitute for a dummy load.
[0013]
(3) An image forming apparatus comprising the control system according to (1) or (2).
[0014]
(4) a transformer having a primary winding and a plurality of secondary windings, a switching element connected between the primary winding of the transformer and a DC power supply for performing switching, and a secondary winding of the transformer A rectifying and smoothing unit for rectifying and smoothing the AC voltage generated in each of the above, a dummy load connected to the rectifying and smoothing unit, and a DC output of at least one of a plurality of DC outputs output from the rectifying and smoothing unit. A multi-output power supply device having a control unit that controls the switching element according to the
A microcontroller powered by at least one or more of the plurality of DC outputs of the multiple output power supply;
A reset circuit that monitors a DC output applied to the microcontroller,
A control system comprising: connecting a dummy load to the rectifying / smoothing unit when the multi-output power supply device is started; and disconnecting the dummy load from the rectifying / smoothing unit by an output of the reset circuit after starting.
[0015]
(5) An image forming apparatus comprising the control system according to (4).
[0016]
(6) a transformer having a primary winding and a plurality of secondary windings, a switching element connected between the primary winding of the transformer and a DC power supply for performing switching, and a secondary winding of the transformer A rectifying and smoothing unit for rectifying and smoothing the AC voltage generated in each of the above, a dummy load connected to the rectifying and smoothing unit, and a DC output of at least one of a plurality of DC outputs output from the rectifying and smoothing unit. A control unit for controlling the switching element according to the control method of the dummy load in the multi-output power supply device comprising:
Step A of connecting the dummy load to the rectifying and smoothing unit at the time of starting the multi-output power supply device;
When the load of the multi-output power supply increases after startup, a step B of disconnecting the dummy load from the rectifying and smoothing unit;
A method for controlling a dummy load in a multi-output power supply device, comprising:
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to examples of an image forming apparatus. The present invention is not limited to the form of the device and the system, but can be implemented in the form of a method, supported by the description of the embodiment.
[0018]
【Example】
(Example 1)
In the first embodiment, an image forming apparatus will be described as an example using a microcontroller, a motor device, and a multiple output power supply device. FIG. 2 is a cross-sectional view illustrating a configuration of an “image forming apparatus” according to the first embodiment, and illustrates a case where the image forming apparatus is a laser beam printer. Hereinafter, the configuration and operation will be described.
[0019]
A laser beam printer main body 24 serving as an image forming apparatus has a paper feed cassette 25 for setting recording paper P, a paper presence / absence sensor 26 for detecting the presence or absence of the recording paper P in the paper feed cassette 25, and recording from the paper feed cassette 25. A paper feed roller 27 for taking out the paper P, a registration sensor 29 for detecting that the recording paper P has reached the registration roller 28 downstream of the paper supply roller 27, and a notification that the recording paper P aligned by the registration roller 28 has reached the image writing position. A TOP sensor 30 for detecting is provided. The process cartridge 31 includes a photosensitive drum 32, a primary charging roller 33, a developing device 34, and a cleaner 35 necessary for an electrophotographic method. A laser beam from a laser unit 37 in a laser scanner section 36 is irradiated on a polygon mirror 38, and is irradiated on a photosensitive drum 32 via an imaging lens 39 and a return mirror 40 to form a latent image. The image is visualized on the photosensitive drum 32 by the device 34, and the toner image is transferred onto the recording paper P by the transfer roller 41. Downstream of the transfer roller 41, a fixing device 42 for thermally fixing the toner image formed on the recording paper P is provided. The fixing device 42 is provided with a heater heating element 44 provided in a polyimide film 43 which rotates together with the recording paper P. The toner image on the recording sheet P is fixed on the recording sheet P by the pressure roller 45. Further, a paper discharge sensor 46 for detecting the paper conveyance state and a paper discharge roller 47 for discharging the recording paper P are provided downstream of the fixing device 42. The fan motor 48 plays a role in lowering the temperature inside the printer main body 24.
[0020]
The engine controller 49 controls various operations of the printer. The motor 50 controls the rotation of the paper feed roller 27, the photosensitive drum 32, the fixing device 42, the paper discharge roller 47, and the like, and performs an operation of transporting the recording paper P. Although not shown, the motor 50 is controlled by a microcontroller 70 mounted on the engine controller 49 and the like. The motor 50 can be controlled in an open loop, and a relatively inexpensive stepping motor is often used as a drive source. The multi-output power supply 51 plays a role of generating and supplying a plurality of DC outputs such as a DC voltage of 5 V used by the engine controller 49 and a DC output of 24 V used by the motor 50.
[0021]
As the multiple output power supply 51, an RCC type power supply as shown in FIG. 1 is used. In the present embodiment, the RCC system will be described, but the multi-output power supply device 51 may be other various systems such as a separately excited flyback system and a forward system.
[0022]
FIG. 3 shows the relationship between the microcontroller 70 mounted on the engine controller 49 and the stepping motor 50. A motor driver 52 exists between the engine controller 49 and the motor 50, and performs speed control, constant current control, and the like based on an A-phase signal, a B-phase signal, and a Vref signal from the CPU. FIG. 4 shows the relationship between the A-phase signal and the B-phase signal in the two-phase excitation method taken as an example this time. In STEP1, the A-phase and the B-phase are excited. A-phase, B-phase (STEP1) → A-phase, / B-phase (STEP2) → / A-phase, / B-phase (STEP3) → / A-phase, B-phase (STEP4) → A By sequentially exciting the phase and the B phase (STEP 1), the stepping motor rotates.
[0023]
FIG. 5 shows a simplified block diagram of the motor driver 52 for the stepping motor. The windings 53 and 54 indicate A-phase winding and B-phase winding in the stepping motor, respectively, and 55 to 62 indicate MOS-FETs for realizing bipolar driving. The A-phase winding and the B-phase winding are excited by the MOS-FETs 55 to 62 in the directions indicated by the arrows in FIG. The resistors 63 and 64 indicate detection resistors for detecting currents flowing through the A-phase winding and the B-phase winding, and Vsense indicates a voltage value generated at both ends of the detection resistors 63 and 64. Reference numeral 65 in the figure denotes a booster circuit composed of a diode, a capacitor, and a switch, which is higher than a DC voltage of 24 V (for example, 28 V or the like) for driving the high-side MOS-FETs 55, 57, 59, 61. ) Has been generated. Reference numerals 66 to 73 in the figure denote logic circuits for sequentially exciting the A-phase winding and the B-phase winding as shown in FIG. 4, and the respective outputs are connected to the gates of the MOS-FETs 55 to 62. I have. Each of the logic circuits 66 to 73 has an enable terminal for controlling whether or not output is possible. The logic circuits 66 to 73 do not operate when the outputs of the comparators 74 and 75 are Hi, but operate when the outputs are Low.
[0024]
The Vref1 signal from the CPU is input to the inverting input terminals of the comparators 74 and 75, and Vsense, which is the voltage across the detection resistors 63 and 64, is input to the non-inverting input terminals. That is, when Vsense is smaller than Vref1, the logic circuit operates, and when Vsense is larger than Vref1, the logic circuit does not operate. That is, the MOS-FETs 55 to 62 do not operate.
[0025]
FIG. 6 shows current waveforms flowing through the A-phase winding and the B-phase winding when two-phase excitation is performed. FIG. 6 shows waveforms when the image forming apparatus is performing a printing operation. The waveforms will be described below. A pulse signal is output from the microcontroller 70 to the A phase and the B phase at a pulse rate according to the set speed of the image forming apparatus main body 24, respectively. The waveform is as shown in FIG. 6, and the excitation is performed in the order shown in FIG. The current flowing through the A-phase winding and the B-phase winding gradually increases after the MOS-FET is turned on, and when Vsense, which is the voltage across the detection resistor, becomes equal to Vref1 which is the signal from the CPU. Turn off the MOS-FET. Thereafter, since Vsense becomes smaller than Vref1, the MOS-FET turns on again. By repeating such an operation in the excitation period of each phase, constant current control is realized.
[0026]
In the present embodiment, after the multi-output power supply device 51 is started, the Vref voltage is reduced by the microcontroller 70 (Vref2) as shown in FIG. The dummy load is separated by the following. That is, after the multi-output power supply device 51 is started, the purpose is to cause the 24 V DC output to consume the motor driver as a load and to disconnect the resistor connected as a dummy load.
[0027]
FIG. 1 shows a circuit configuration of a multi-output power supply device 51 which is a main part of the present embodiment. The difference from the conventional example shown in FIG. 10 is that a collector of an NPN transistor 76 is connected in series with a dummy resistor 23. The emitter is connected to the GND terminal, and a voltage obtained by dividing a 24 V DC output using resistors 77 and 78 is input to the base. The collector of the NPN transistor 79 is connected to the base of the NPN transistor 76, and the emitter is connected to GND. The base of the NPN transistor 79 is connected to the output port of the microcontroller 70 via the resistor 80. The base is pulled down by a resistor 81.
[0028]
When the multi-output power supply device 51 is started, the base voltage divided by the resistors 77 and 78 is applied to the base of the transistor 76 to turn on the NPN transistor 76, and the NPN transistor 79 is turned on because no voltage is applied to the base. The state does not change, and the dummy resistor 23 is inserted between the 24 V output and GND. After the multi-output power supply device 51 is started, the load is consumed by the motor driver 52 by the microcontroller 70, and then the output port is set to Hi to turn on the NPN transistor 79 and turn off the NPN transistor 76. Accordingly, the dummy resistor 23 can be disconnected from the DC output of 24V.
[0029]
At the time of printing by this laser beam printer, a specified drive current is supplied to the stepping motor by increasing Vref. FIG. 6 shows the drive current waveform at this time.
[0030]
As described above, according to the present embodiment, the startup characteristics of the multi-output power supply device can be stabilized, and power consumption by the dummy load can be eliminated after startup, so that the dummy resistor always generates heat. The temperature rise of the peripheral parts due to this can be suppressed.
[0031]
In addition, since the stepping motor and the stepping motor drive control unit have sufficient measures against heat generation in view of the normal rotation operation, heat generation with a small drive current is not so large, and can be easily performed without taking any thermal measures. Can be realized.
[0032]
Further, it is possible to eliminate unnecessary power consumption due to a dummy resistor during a printing operation of a laser beam printer or the like.
[0033]
In the present embodiment, the Vref is changed without changing the pulse rate of the stepping motor to generate a 24V load which is a dummy load. However, the pulse rate may be changed, or the stepping motor may be held. A load may be generated.
[0034]
(Example 2)
Second Embodiment An “image forming apparatus” according to a second embodiment will be described. The hardware configuration of the present embodiment is the same as that of the first embodiment except for the configuration of the multi-output power supply device, and thus the description of the first embodiment is cited. The difference from the first embodiment is that on / off control of the dummy load is performed by a reset circuit instead of a microcontroller.
[0035]
FIG. 8 is a circuit diagram of the multi-output power supply device used in the present embodiment. As shown, a reset circuit 90 is connected instead of the microcontroller 70 (FIG. 1). Although not shown, the reset circuit 90 monitors the voltage supplied to the microcontroller 70, and starts operating with a slight voltage after startup. From the start of the operation, the output is Lo until the input voltage reaches a certain value. The Lo state is maintained for a predetermined period when the input voltage reaches the certain value. Transition.
[0036]
FIG. 9 shows the change of the reset signal and the rise characteristics of the DC output at the time of startup. As shown in the figure, the dummy resistor 23 is inserted between the 24V output and GND during the reset, and after the reset is released, the microcontroller 70 starts the operation. Disconnected from. During the reset period of the microcontroller 70, the base voltage divided by the resistors 77 and 78 is applied to the base of the transistor 76 to turn on the NPN transistor 76, and the output of the reset circuit 90 of the NPN transistor 79 becomes Lo. Since there is no voltage applied to the base, the base is not turned on, and the dummy resistor 23 is inserted between the 24 V output and GND. After the reset is released, the output of the reset circuit 90 becomes Hi, so that the NPN transistor 79 is turned on and the NPN transistor 76 is turned off, whereby the dummy resistor 23 can be disconnected from the DC output of 24V.
[0037]
As described above, according to this embodiment, the same effect as that of the first embodiment can be obtained only by hardware without using the software of the microcontroller 70, and it is not necessary to incorporate a complicated sequence into software. Therefore, the ROM capacity can be reduced.
[0038]
【The invention's effect】
As described above, according to the present invention, the startup characteristics of the multi-output power supply device can be stabilized, and power consumption by the dummy load can be eliminated after startup, so that the dummy resistor always generates heat. Temperature rise of the peripheral parts due to the presence of the heat sink can be suppressed.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a multi-output power supply device used in Embodiment 1. FIG. 2 is a cross-sectional view showing the configuration of Embodiment 1. FIG. 3 is a diagram showing the relationship between a microcomputer and a stepping motor. FIG. 5 is a block diagram showing the configuration of a motor driver. FIG. 6 is a diagram showing waveforms during normal operation of a stepping motor. FIG. 7 is a diagram showing a dummy load of the stepping motor. FIG. 8 is a diagram showing a waveform when a substitute is used. FIG. 8 is a circuit diagram of a multi-output power supply device used in Embodiment 2. FIG. 9 is an explanatory diagram of a multi-output power supply device at startup. FIG. [Circuit diagram] [FIG. 11] Diagram showing waveforms at various parts of the circuit of FIG.
23 Dummy resistor 50 Stepper motor 51 Multiple output power supply 52 Stepper motor driver 70 Microcontroller

Claims (1)

A transformer having a primary winding and a plurality of secondary windings, a switching element connected between the primary winding of the transformer and a DC power supply for performing switching, and a switching element generated in the secondary winding of the transformer. A rectifying / smoothing unit for rectifying and smoothing the AC voltage, a dummy load connected to the rectifying / smoothing unit, and a DC output of at least one of a plurality of DC outputs output from the rectifying / smoothing unit. A multi-output power supply device comprising a control unit for controlling the switching element,
A microcontroller powered by at least one or more of the plurality of DC outputs of the multiple output power supply;
A motor device supplied with a DC output from the multiple output power supply device and controlled by the microcontroller,
In the control system composed of
The dummy load is connected to the rectifying and smoothing unit at the time of starting the multi-output power supply device, and when the load of the multi-output power supply device increases after the starting, the dummy load is separated from the rectifying and smoothing unit by the microcontroller. A control system characterized by the following.

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