JPS63302727A - Power source unit - Google Patents

Abstract

PURPOSE:To take out a plurality of souce voltages from single converter transformer, by differentiating the polarities of secondary winding and rectifying means for supplying power to high voltage and low voltage loads. CONSTITUTION:When an A.C. voltage is inputted to terminals P1, P2 in order to excite a switching transistor (Tr)Q1 and produce outputs from respective secondary windings, rectified/smoothed output voltage to be inputted when TrQ1 is conducting is applied onto a primary winding L1, and a voltage boosted or stepped down corresponding to winding ratio is produced at the secondary. Consequently, rectified secondary output depends on the state of load when TrQ1 is conducting and not influenced by duty factor of TrQ1. In other word, forward winding outputs of windings L4-L6 are not susceptible to variation of load condition of secondary windings L7, L8, L3 for supplying power to low voltage load. Consequently, output at high voltage side can be controlled without exerting influence on a low voltage load.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device, and particularly to a power supply device that supplies power to high-voltage and low-voltage loads in an electrophotographic image forming apparatus.

[Prior Art] In electrophotographic image forming apparatuses such as copying machines and laser beam printers, 5V, 12V, and 24V power is supplied to sequence control circuits, document conveyance motors, and other circuits.
A constant-voltage power source of about V and a high-voltage power source of kiloports are required to supply power to a charger, a developing device, a fluorescent lamp for illuminating the document, and the like.

[Problem to be solved by the invention] In the conventional device, the various power supplies described above are configured.

Therefore, a low-voltage stabilized DC voltage is extracted from the AC power supply and supplied to the low-voltage load, and this is then converted to DC-D again.
A circuit is used that boosts the voltage using a C inverter circuit or the like and supplies power to a high-voltage load. The reason for this configuration is that the high-voltage output that supplies power to the charger, developer, etc. must be turned on, off, or output controlled according to the image forming process, and the power supply to each load must be controlled independently. Because it has to be done.

Although it is possible to provide low-voltage and high-voltage output windings on the secondary side of a single converter transformer to supply power to low-voltage and high-voltage loads, the high-voltage output may be controlled by electrical switching means such as transistors. This was extremely difficult, and at least the low-voltage and high-voltage power supplies had to be constructed independently.

Therefore, in the conventional image forming apparatus, there are problems in that the number of step-up transformers is large, the cost is high, and the area occupied by the power supply section and the weight thereof are increased.

[Means for Solving the Problems 1] In order to solve the above problems, in the present invention, in a power supply device that supplies DC power to a plurality of high-voltage and low-voltage loads of an electrophotographic image forming apparatus, a converter transformer, A switching means provided on the primary side of the converter transformer for exciting the primary winding of the converter transformer and for supplying DC power to high-voltage and low-voltage loads respectively connected to the plurality of secondary windings of the converter transformer. A mode in which the primary side switching means and the secondary side rectifying means are alternately conductive on the low voltage side by providing a rectifying means and making the polarities of the secondary winding and the rectifying means different for feeding power to the high voltage and low voltage loads, On the high voltage side, a configuration was adopted in which power is supplied in a mode in which the primary side switching means and the secondary side rectifying means are alternately conductive.

[Function] According to the above configuration, the polarity of the secondary winding of the converter transformer and the rectifier is made different between the high voltage load and the low voltage load, and the forward mode in which the primary side switching means and the rectifier are simultaneously conducted on the low voltage side; At high voltages, power is supplied in flyback mode that alternates the timing of conduction between the primary and secondary sides.In flyback mode, the secondary side output can be controlled according to the energization time on the primary side, but in forward mode, energization is performed in the flyback mode. Since there is a characteristic that time has little effect on the secondary side output, even if high voltage side output control is performed in flyback mode, the power supply on the low voltage side is hardly affected.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 shows the configuration of a power supply device adopting the present invention. In this embodiment, a single converter transformer T1 is provided with a plurality of secondary windings for high voltage and low voltage. Power multiple loads at low voltage. transformer TI
A DC voltage is input to the primary winding Ll, which is obtained by exchanging the AC voltage input to the terminals PI and P2 by a rectifier/smoothing circuit 1 composed of diodes, capacitors, and the like. The application of the input voltage to the primary winding Ll is controlled by the transistor Ql. A resonance capacitor C2 is connected between the collector and emitter of the transistor Ql. The energization ratio of the transistor Ql is controlled by the switching regulator 2. The switching regulator 2 is powered by the power generated in the secondary winding L2. One end of the secondary winding L2 is connected to the common potential of the primary winding L1, and the other end is connected to a resistor R3 and a diode D.
A rectifier circuit consisting of I is connected. The output of the diode D1 is input to a connection point between a resistor R1 and a capacitor C2 that divides the input voltage of the primary winding L1. The switching regulator 2 is driven by the voltage generated at the connection point between the resistor R1 and the capacitor CI at the time of rising, and after the output is stabilized, it is operated by the rectified output of the secondary winding L2.

Furthermore, the switching regulator 2 controls the base of the transistor Ql according to the output of a shunt regulator 7, which will be described later. The shunt regulator 7 and the switching regulator 2 are insulated by a photocoupler 3.

The collector and emitter of the phototransistor of the photocoupler 3 are connected to the switching regulator 2, and the emitter is connected to the common potential of the primary winding through a resistor R2.

The transformer TI is further provided with multiple secondary windings indicated by symbols L3 to L9, and the zero line ratio is set according to the required voltage. Further, the polarity of each secondary winding is set so that the beginning of the winding is indicated by a black circle in the figure.

The secondary winding L3 is for supplying a developing bias in which alternating current and direct current are superimposed to the developing device, and is connected to a circuit that generates a negative direct current voltage and a circuit that generates a high voltage alternating current. One end of the secondary winding L3 is installed as shown, and this potential is a common potential. The circuit shown above the common potential is a circuit that generates a negative DC voltage, and the diode D
Rectification/smoothing circuit with 2° capacitor C5, series regulator 4. Resistance R・4. It consists of a filter circuit using capacitor C4. An output terminal pH is connected to one end of the resistor R4, and a high voltage alternating current signal generated by the circuit shown below the common potential line is coupled thereto via a capacitor C3.

Further, the output of the secondary winding L3 is connected to the diode D3°D4. After being voltage doubled and rectified by capacitors C6 and C7, it is connected to the collector of transistor Q2 via resistor R5. This transistor Q2 is switched by the output of the oscillation circuit 5, and as a result, a high voltage AC output is generated at the collector of the transistor Q2. This alternating current is capacitor c
In the generation of a developing bias of 0 or more which is superimposed on the DC voltage via Q3 and applied to the developing device, the DC component is approximately -600V, and the AC signal generated by transistor Q2 is approximately 1.2KV. The switching frequency of the transistor Q2 is approximately 1800H2, and the oscillation waveform is a rectangular wave or other waveform.

The secondary windings L4 and L5 are for supplying power to low voltage loads of h24V and 12V, respectively, and are connected to resistors R8 and L5, respectively.
R7, diode D5. It has a rectifier/smoothing circuit consisting of DB and capacitors C8 and C9. The rectified and smoothed DC voltage is applied to terminals P3, P4 and P5. Power is supplied to each load via P6. The 24v load is the fixing heater control unit, which requires constant power supply from the moment the power is turned on.

Possible examples include the operation unit and the motor of the cooling fan.

Further, a display lamp or the like can be considered as the 12V load.

The secondary winding L6 also has a rectifier/smoothing circuit consisting of a resistor R8, a diode D7, and a capacitor CIO, and further has a series regulator 6 for stabilization. The output voltage after stabilization is set to 5V, and this 5V output voltage is supplied to a sequence control section consisting of a microprocessor, memory, etc. via terminals P7 and P8.

The secondary windings L4 to L6 described above are each controlled in forward mode so that the diodes D5 to D7 are conductive when the switching transistor Ql on the primary side of the transformer is conductive, so the output voltage is It is proportional to the line input voltage 1ttfrL applied to both ends of the line, and is independent of the energization ratio of the transistor Ql.

The secondary winding L7 is provided to output a DC voltage of 5 V during standby and 24 V during image forming operation in order to control the image forming process. The secondary winding L7 is provided with a rectifier/smoothing circuit composed of a diode D8 and a capacitor C12, and the output voltage from the terminal P9 is controlled by a shunt regulator 7.The shunt regulator 7 receives the voltage input from the terminal PIO. The voltage generated at the output terminal P9 is switched to 5V during standby and to 24V during the image forming period.

The operation of the shunt regulator 7 is transmitted by the photocoupler 3 to the switching regulator 2 on the primary side of the transformer.

The secondary winding L8 is for applying a charging current to the transfer charger and other chargers, and is also connected to a diode D9. It is connected to a rectifier/smoothing circuit made up of a capacitor C13 and a discharge resistance made up of a resistor R9. The output voltage is terminal P
It is output from 12. The charging current is detected by the detection resistor RIO, and the series regulator 9 is set to 2 depending on the detected value.
One end of the next winding L8 is controlled to control the charging current as desired.

Furthermore, the secondary @1aL9 is for lighting the fluorescent lamp 11 for document illumination, and supplies power to the fluorescent lamp 11 via the ballast lO, and determines whether to preheat the fluorescent lamp 11 or to turn it on. is switched by controlling one end of the filament of the fluorescent lamp 11 with a diode bridge 12 and a transistor Q3. Transistor Q3 is controlled by a control signal input from terminal P13.

Secondary winding L3. L7. ．． The polarity of the windings of L8 is selected so that the rectifier diodes connected to each winding operate in a flyback mode in which they conduct when the primary switching transistor Q1 is cut off. In particular, 2
The output state of the secondary winding L7 is fed back to the primary side by the photocoupler 3, and the excitation state of the transformer Tl is controlled according to this output state.

In the above configuration, each of the low-voltage power supplies for sequence control operates in a forward mode in which when the switching transistor on the primary side of the transformer is turned on, the rectifier diode is turned on at the same time to charge the smoothing capacitor and supply power to the load.
On the other hand, the high-voltage secondary winding conducts the wave rectifying diode when the switching transistor is cut off, charges the smoothing capacitor, and supplies power to the load.

Therefore, when an AC voltage is input to the terminals PI and P2 to excite the switching transistor Q1 and generate an output in each secondary winding, the switching transistor Ql
When conductive, the input rectified and smoothed output voltage is applied to the primary winding, and a boosted or stepped down voltage is generated on the secondary side according to each winding ratio. Therefore, the rectified output on the secondary side when the switching transistor Q1 is conductive depends on the load condition, and is not greatly affected even if the conduction ratio of the switching transistor changes. In other words, the forward winding of the windings L4 to L6 The line output is not significantly affected by changes in the load conditions of the secondary windings L7, L8 and L3, which supply power to the step-down load. Therefore, the output on the high voltage side is controlled without affecting the low voltage load. be able to.

At the same time as the power is turned on, the image forming mechanism (not shown) enters a standby state, and the control circuit for sequence control is connected to terminal P.
7. Starts operation by power supply voltage controlled from P8.

In the standby state, loads that consume a lot of power, such as a sequence control motor, clutch, and solenoid, and loads for charging, exposure, and development are stopped. In this rest state, the series regulator 41 oscillation circuit 5. The series regulator 9 stops power supply to high-voltage loads such as the developing device and the charger.

In addition, the shunt regulator 7 is 5V in standby state.
This operating state is fed back to the switching regulator 2 via the photocoupler 3.

Since the high voltage load on the secondary side is at rest, the switching regulator 2 controls the energization ratio of the switching transistor Ql to be very small. For this reason, the flyback voltage generated in proportion to the energization ratio is also very low, and as a result, the high voltage output voltage is supplied from the flyback winding, so it is less than 20 to 30% of the voltage during image forming operation. The voltage drops to a level that does not affect the photosensitive drum at all. At such a low output voltage, almost no load current flows through the charger and the developer, and the image forming process is not affected.

Next, when the image forming state is entered, a voltage of 24 V indicating that the shunt regulator 7 is in operation is outputted from the terminal P9 via the analog switch 8. The operation of the shunt regulator 7 is fed back to the switching regulator 2 via the photocoupler 3, and as a result, the energization ratio of the switching transistor Q1 is increased. This is because various image forming processes such as rotation of the photosensitive drum and movement of the optical system are started, and the load current of the transformer increases.

The switching regulator 2 controls the energization ratio so that the flyback voltage of the transformer T1 remains constant during the image forming period. For this reason, the windings L3, L7 are constructed from flyback windings.

A predetermined voltage drop is generated in L8, and this output voltage can be used to supply power to the developer and charger. In this state, the energization ratio is controlled so that the flyback voltage of the transformer TI is constant, but by this control,
The low-voltage load voltage connected to the secondary windings L4 to L6, which are constituted by forward windings, is hardly affected.

As described above, according to the configuration shown in Figure 1, it is possible to supply various voltages from low voltage to high voltage using a single converter transformer, and moreover, it is possible to supply various voltages from low to high voltages using a single converter transformer. can be controlled.

In the configuration of FIG. 1, the winding L7 is provided to supply voltage to the shunt regulator, but the shunt regulator may be connected to the winding L8 for supplying power to the charger as shown in FIG. In Figure 2, the shunt regulator 7
is connected to one end of a resistor RIO that divides the output of the winding L8. A photocoupler 3 and an analog switch 8 are connected to the shunt regulator 7 in the same manner as in FIG. Even in the configuration shown in Fig. 2, the charging current is switched between when forming one image and during standby, but due to the voltage and current characteristics (load characteristics) of the charger, the charging current does not flow at a voltage of 4 kV or less.
Output control below 4kV becomes impossible. Therefore, in order to ensure a predetermined output during standby, a resistor R23 across the output transistor of the photocoupler 3 is connected.

According to the configuration shown in FIG. 2, the number of windings can be reduced by one, and the transformer T1 can be made smaller and lighter.

Furthermore, as shown in FIG. 3, in addition to the winding L7, the windings L3, L5 . L6 can be omitted.

In FIG. 3, a circuit around the shunt regulator 7 is connected to the winding L8, and a switching regulator 4 is connected to form a developing bias using the voltage divided by the resistors R21 and R22, and an alternating current component of the developing bias is connected. is supplied to transistor Q2. Transistor Q2
The base of is driven by an oscillator 5 as in FIGS. 1 and 2.

Further, a low voltage output of 5V to 12V (7) can be generated by voltage converting the rectified output of the first winding L4 using the switching regulator 21.

[Effects of the Invention] As is clear from the above description, according to the present invention, in a power supply device that supplies DC power to a plurality of high-voltage and low-voltage loads of an electrophotographic image forming apparatus, a converter transformer and a converter transformer are provided. a switching means provided on the primary side of the converter transformer for exciting the primary winding of the converter transformer, and a rectifier for supplying DC power to high-voltage and low-voltage loads respectively connected to the plurality of secondary windings of the converter transformer. By providing means for differentiating the polarity of the secondary winding and the rectifying means that feed power to the high-voltage and low-voltage loads, a mode is established in which the primary switching means and the secondary rectifying means are alternately conductive on the low-voltage side, and on the high-voltage side. Since the configuration is adopted in which power is supplied in a mode in which the primary side switching means and the secondary side rectifying means are alternately conductive, it is possible to extract multiple power supply voltages ranging from high voltage to low voltage from a single converter transformer. This has the excellent effect of being able to control each load independently without affecting each other.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a power supply device employing the present invention, and FIGS. 2 and 3 are circuit diagrams showing modifications of the configuration of FIG. 1, respectively. l... Rectifier/smoothing circuit 2... Switching regulator 3... Photocoupler 4.6.9... Series regulator 5... Oscillator 7... Shunt regulator 8... Analog switch lO...・Ballast 11...Fluorescent lamp TI...
Trance

Claims (1)

[Claims] A power supply device that supplies DC power to multiple high-voltage and low-voltage loads of an electrophotographic image forming apparatus includes a converter transformer and a switching device provided on the primary side of the converter transformer that excites the primary winding of the converter transformer. and rectifying means for supplying DC power to high voltage and low voltage loads respectively connected to the plurality of secondary windings of the converter transformer, and a secondary winding and rectifying means for supplying power to the high voltage and low voltage loads. By making the polarities different, power can be supplied in a mode in which the primary side switching means and the secondary side rectifying means are conductive at the same time on the low voltage side, and in a mode in which the primary side switching means and the secondary side rectifying means are alternately conductive on the high voltage side. A power supply device characterized by: