JPH01216369A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the number of transformers in a power source part and to drive the transformer on a driving condition fit-test for a DC output by supplying low voltage and high voltage direct current from the same switching transformer different from an AC power source. CONSTITUTION:The title device is constituted of a common switching transformer 2 for performing power supply to the high voltage and low voltage DC loads and control means 26 and 27 for stopping the high voltage output of the switching transformer 2 till the output of the low voltage side is stabilized. Namely, the low voltage and the high voltage direct current is supplied from the same switching transformer 2 which is different from the AC power source. Thus, the number of the transformers in the power source part can be reduced and the transformer for outputting the direct current can be driven by utilizing a transformer driving condition fit-test for the DC output, for example, driving frequency, etc.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides an image format t? The present invention relates to an image forming apparatus having a power supply device that supplies direct current and alternating current to high-voltage loads such as charging circuits, and direct current to low-voltage loads such as control systems and sheet conveyance circuits.

[Prior Art] Electrophotographic image forming apparatuses such as copying machines and laser beam printers have been known.

This type of device requires high-voltage alternating current and direct current for the charging system, developing system, transfer system, etc., and low-voltage direct current of a different voltage is required for the document transport system motor, control circuit, etc. The structure was quite complex.

FIGS. 7 and 8 show different configurations of the power supply section of a conventional image forming apparatus. In FIG. 7, reference numeral 50 denotes a transformer drive control circuit that intermittently applies direct current obtained by directly rectifying a commercial power source to the primary side of the switching transformer 51.

The switching transformer 51 has a winding ratio determined to be able to generate low voltages of 5V and 24V, and the output of the secondary winding 54 is converted to direct current by a rectifier and smoothing circuit 52, and further stabilized by a three-terminal regulator 53. After that, it is supplied to a control system such as a microprocessor.

The output of the secondary winding 55 is rectified by a rectifier circuit 56 and smoothed by a choke input type smoothing circuit 57 to generate a 24V DC voltage used in a motor or the like.

This 24V is supplied to a charger 29 provided around the photosensitive drum 28. It is also used to generate the high pressure necessary for the developing device 30 and transfer roller 31.

High voltage DC and charger 29 required for transfer roller 31.
A switching transformer 59 is used to generate the high voltage DC bias necessary for the developer 30. The aforementioned 24V is intermittently applied to the primary winding of the switching transformer 59 by a transformer drive control circuit 58 configured similarly to the transformer drive control circuit 50.

The output of the secondary winding 64 of the switching transformer 59 is converted into direct current by a rectifying and smoothing circuit 65, and the output is transferred to the transfer roller 31.
is applied to On the other hand, the outputs of the secondary windings 60 and 62 are respectively converted into DC by rectifying and smoothing circuits 61 and 63, and applied to one end of the winding of an AC transformer 68 and 69.

The AC transformer 68 is connected to the charger 29. A transformer drive control circuit 66.6 generates an alternating current component to be applied to the developing device 30 and is configured similarly to the transformer drive control circuit 58.
7 on the primary side. Power in which AC and DC bias are superimposed is generated in the winding of the AC transformer 68, and is applied to the charger 29 and the developer 30, respectively.

On the other hand, in FIG. 8, the 5V and 24V systems are the same as in FIG.
generated by. Each transformer is driven by a primary-side transformer drive control circuit 58a, 58b. The switching transformer 59a includes a secondary winding 71 that supplies an AC component to the charger 29, a secondary winding 72 that supplies the DC bias of the charger 29 via a rectification and smoothing circuit 76, and a rectification and smoothing circuit to the transfer roller 31. It has a secondary winding 73 that supplies high voltage direct current via 77.

On the other hand, the switching transformer 59b has a secondary winding 74 that supplies an AC component to the developing device 30, and a secondary winding 75 that generates a developing bias via a rectifying and smoothing circuit 78.

[Problems to be Solved by the Invention] In the configuration shown in Fig. 7, high voltage DC bias is obtained from the commercial power supply through two stages of inverter transformers, resulting in large power loss and poor efficiency. An independent power supply circuit is required for the high-voltage direct current and alternating current applied to the device, which increases manufacturing costs and increases the size of the power supply unit.

In the configuration shown in FIG. 8, the charger 29. The AC component to be applied to the developing device 30 is usually a relatively low frequency of around 1 kHz, and the optimum frequency and conduction timing of the charging device 29 and the developing device 30 are different, so separate circuits must be used for each transformer. However, since a single transformer is used to generate AC and DC components to be applied to the charger 29, the capacitance of the capacitors in the rectifying and smoothing circuits 76 and 77 that rectify the low frequency output of around 1 kHz becomes large. This increases costs and makes it difficult to reduce the size and weight of the device.

In addition, in the configuration shown in FIG. 8, the switching transformer 59a,
There is a problem in that a high voltage DC bias can only be obtained at the timing when 59b becomes conductive. Also, the 8th
In the configuration shown in the figure, the alternating current and direct current components are generated from the same transformer, and there is a problem in that the capacity of the transformer becomes large to generate the direct current component, and therefore the device becomes large.

The object of the present invention is to solve the above problems.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides direct current and alternating current to high voltage loads such as charging circuits, and direct current to low voltage loads such as control systems and sheet conveyance circuits. In the image forming apparatus, the image forming apparatus includes a common switching transformer that supplies power to the high-voltage and low-voltage DC loads, and the high-voltage output of this switching transformer is stopped for a period until the output on the low-voltage side becomes stable. A configuration with a control means was adopted.

[Function] According to the above configuration, low-voltage and high-voltage DC are supplied from the same switching transformer that is separate from the AC power supply, so the number of transformers in the power supply section is reduced, and the DC output is The transformer for DC output can be driven using the most suitable transformer driving conditions, such as the driving frequency. Further, high voltage output is prohibited during a period when low voltage output supplied to a control system or the like is not stable, thereby preventing adverse effects on high voltage loads such as chargers, photosensitive drums, etc.

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

FIG. 1 shows the configuration of a power supply section of an image forming apparatus adopting the present invention. In FIG. The switching transformer 2 is driven by adding the current. Secondary windings 91 to 95 are connected to the switching transformer 2, and in this embodiment, low voltage DC of 5V and 24V and high voltage DC to be supplied to the charger 29, the developer 30 and the transfer roller 31 are simultaneously generated.

The secondary winding 91 is connected to a 5V generation circuit 3 that generates 5V to be supplied to the control system. The secondary winding 92 is connected to a 24V generation circuit 4 that supplies a motor and the like. The 5V generation circuit 3 is constituted by a rectification and smoothing circuit 96° and a three-terminal regulator 98, and the 24V generation circuit 4 is constituted by a rectification and smoothing circuit 97.

The secondary winding 93 generates a DC bias to be supplied to the charger 29. That is, a rectifying and smoothing circuit consisting of a diode 5 and a capacitor 6 and a load resistor 7 are connected to the secondary winding 93, and the output Vl is connected to one end of the secondary winding of the AC transformer 24. The corephthal emitter of the transistor 8 is connected between the common potential side of the secondary winding 93 and the ground potential.

The base of transistor 8 is connected to operational amplifier l via resistor 9.
Controlled by O. A control voltage v2 for controlling the DC bias of the charger and a voltage divided by the resistors 11 and 12 of the previous output voltage v1 are input to the operational amplifier 10. Resistance R
An AC bypass capacitor 13 is connected to 11 and 12.

The primary side of the AC transformer 24 is driven by a transformer drive control circuit 26 that intermittently inputs a low voltage such as 24V. One end of the secondary winding of the AC transformer 24 is connected to a charger 29 . The DC bias supplied to the developing device 30 is generated by the same circuit 14 on the charger side, which is made up of elements indicated by numerals 5 to 13.

The output of circuit 14 is connected to one end of AC transformer 25 . The primary side of the AC transformer 25 is the transformer drive control circuit 2
The developing device 30 is controlled by a transformer drive control circuit 27 similar to that shown in FIG.

The high voltage DC voltage v4 supplied to the transfer roller 31 is supplied from the secondary winding 95 of the switching transformer 2. A rectifying and smoothing circuit including a diode 15 and a capacitor 16 and a load resistor 18 are connected to the secondary winding 95 . A resistor 17 is connected between the common potential of the secondary winding 95 and the ground potential. The voltage v4 supplied to the transfer roller 3 is applied to the resistor 19.
20 and input to one input terminal of the operational amplifier 21.

The control voltage v5 of the transfer roller 31 is input to the other input terminal. The output of the operational amplifier 21 is
Controls the base of transistor 23 whose corefthal emitter is connected between the rectified output of secondary winding 95 and ground.

Next, operations in one or more configurations will be described. When commercial power is supplied to the transformer drive control circuit 1 to excite the switching transformer 2, voltages are generated in the secondary windings 91 to 95, respectively, depending on the winding ratio. The low voltages of 5V and 24V are each converted into direct current by the generation circuit 3.4, and each is supplied to a predetermined load.

Next, the operation of the circuit connected to the secondary windings 93 and 94 will be explained. Here, the operation on the secondary winding 93 side will be shown.
The DC component Vl supplied to the charger 29 has a resistance of 11.12
and is applied to one input of the operational amplifier 10. The operational amplifier lO compares this voltage with the control voltage V2,
When both inputs are equal, i.e. V2=V1-R12/
It is stabilized by (R11+R12).

As a result, the conductivity of the transistor 8 is controlled, and the DC bias is controlled to a desired value by the control voltage v2. Then, according to the above equation, the output voltage v1 becomes -totov.

When detecting the output using resistors 11 and 12, the AC transformer 24
The AC component generated is bypassed by the capacitor 13 and does not pass through the resistors 11 and 12. If a negative voltage cannot be used as the control voltage v2, an appropriate level shift circuit may be added.

A DC bias on the developing device 30 side is similarly generated by one circuit 14. The circuit connected to the secondary winding 95 is almost the same as that for the secondary winding 93 except that the polarity is ten. That is, the degree of conductivity of the transistor 23 changes depending on the value of the control voltage v4 input to the operational amplifier 21,
The DC voltage v4 supplied to the transfer roller is controlled. Transistor 23, unlike transistor 8, directly controls the potential at the output terminal.

Here, FIG. 2 shows the structure of the transformer drive control circuit 26, 27 of the AC transformer 24, 25.
．． The primary winding 25 is Nj as shown in the figure.
．． 38 via a capacitor 40 and a resistor 41. Current control resistors 36 and 39 are connected to both ends of the series-connected transistors 37 and 38. At the base of the transistor 37.38 is a resistor 33.34.3
The output of the oscillation circuit 32 is supplied through the oscillator 5.

By supplying the oscillation circuit 32 with an appropriate driving frequency, for example, a low frequency pulse of about 1 kHz suitable for the charging process, the AC transformers 24 and 25 are driven at a desired frequency, and the charging device 29 and the developing device 30 are supplied with the desired voltage. Can apply high voltage alternating current with a frequency of

At the connection point between resistor 33 and resistor 34.35, there are symbols 42 to 48.
A circuit made up of elements shown in is connected. This circuit is intended to prevent malfunctions caused by the rising timing of the 24V and 5V power supplies shown in Figure 1.For example, the 5V output is applied to a control system that controls the operation of the entire device, such as a microprocessor. If the voltage rises later than the high-voltage output or the low-voltage output of 24 V, there is a problem that a runaway state occurs, which adversely affects the photosensitive drum 28, the charger, and other loads, and also disrupts image formation.

Therefore, the transistor 42 is controlled according to the output timing of 5V and 24V, and high voltage output is stopped when the power supply is unstable.

That is, the base of the transistor 42 is connected to the collector of a transistor 46 via a resistor 43, and is grounded by a resistor 44. transistor 46
A 24V system output is applied to the collector of , via a resistor 45. The emitter of the transistor 46 is grounded, and a 5V output voltage from a resistor 47.48 is applied to its base.

In this configuration, if 24v rises first and 5v has not yet risen, transistor 46 is cut off, transistor 42 is turned on, and the output of oscillation circuit 32 is not applied to transistor 30.38, and the AC transformer 24.25 is turned off. Output is prohibited. The 5V system rises and the resistance becomes 47.4
When the voltage divided by 8 exceeds the base-emitter conduction voltage of transistor 46, transistor 46 becomes conductive, transistor 42 becomes conductive, and the output of oscillator circuit 32 can be applied to transistors 37 and 38.

For example, if the resistance value of the resistor 47.48 is 10Ω and 2Ω, high voltage AC output becomes possible when the output of the 5V system reaches 3.9V. Such a configuration can also be connected to a high voltage DC component control circuit consisting of an operational amplifier lO1 and a transistor 8 as shown in FIG.

In this case, the collector of transistor 42 is connected to operational amplifier 1.
The transistor 8 is connected between a resistor 9 connected to the output terminal 0 and the base of the transistor 8. Further, as indicated by the parenthesized symbol, the same circuit can be provided in a high-voltage direct current control circuit applied to the transfer roller 31. With such a configuration, runaway of the power supply can be prevented, image defects due to malfunction can be prevented, and the life of the load can be extended.

According to the above configuration, low-voltage direct current and high-voltage direct current components to be supplied to the charger, developer, etc. can be supplied from the same switching transformer 2. Therefore, the number of transformers can be reduced, and the power supply section, and therefore the entire device, can be made smaller and lighter.

In addition, since the high-voltage DC that is supplied to the charger, developer, etc. is generated by dedicated AC transformers 24 and 25, there are problems such as lowering the efficiency of the DC system due to the low frequency characteristics of the AC system as in the past. This enables efficient power supply, and eliminates the need for excessive power supply capacity to supply both alternating current and direct current, unlike conventional methods.

Furthermore, since the AC and DC systems are independent, the transformer can be driven by highly efficient high frequency waves in the DC system, increasing the efficiency of power supply, and the DC output timing can be adjusted to match the ON of the AC transformer.・You can get the advantage of not being affected by off-time.

In addition to the above configuration, a high voltage diode 5.15 and a capacitor 6.15 are used to rectify the secondary output of the switching transformer 2.
16. Resistance 7! 8 etc. into the housing of the switching transformer 2 and integrally formed with resin etc.,
The configuration of the power supply section can be made smaller and lighter.

Furthermore, in one or more of the embodiments, a configuration is added that prevents the high voltage output from running out of control even if there are variations in the timing of power supply rise, so that the reliability of the device can be improved.

Figures 4 to 61! ! ! 1 shows the structure of a different embodiment.

The parts in each figure that are different from FIG. 1 will be explained below.

In FIG. 4, the secondary winding 91 for the 5V output in FIG. 1 is omitted, and the 3-terminal regulator 9 is connected to the 24V output winding 92.
A 5V generation circuit 3 consisting of 8 is connected. According to such a configuration, the number of secondary windings can be reduced and the switching transformer 2 can be further miniaturized.

In FIG. 5, an AC transformer 24 is provided with two secondary windings, each of which generates an AC component to be supplied to a charger 29 and a developer 30. According to this configuration, the number of transformers can be further reduced by one. The 5v system is constructed in the same manner as shown in FIG.

In FIG. 6, a configuration for switching the polarity of the high voltage output to the transfer roller 31 is added.

Conventionally, there has been a problem that when a positive voltage is applied to the transfer roller when the recording paper is not between the photosensitive drum 28 and the transfer roller 31, the toner on the photosensitive drum adheres to the transfer roller, and the recording paper is contaminated by this toner. It has been known.

In view of this point, a method has been considered in which a negative voltage is applied to the transfer roller 31 when no transfer is performed. When performing such control, switching transformer 2 is
Next windings 101 and 102 are provided, and a diode 15 is connected to these.
．． Connect negative and positive rectifying and smoothing circuits consisting of 18 and capacitors 16 and 19. Only the common potential of the secondary winding 102 is grounded, and connected to the common potential side of the secondary winding 101 via the rectified output resistor 20 of the secondary winding 102.

Then, an output voltage is supplied to the transfer roller 31 via the discharge resistor 17. The collector and emitter of transistor 21 are connected between secondary winding 101 and ground. According to such a configuration, when transferring, a positive potential is applied to the transfer roller 31 by cutting off the transistor 21, and when not transferring, a negative potential is transferred by making the transistor 21 conductive. By supplying the toner to the roller 31, it is possible to prevent the recording paper from becoming dirty due to toner adhesion.

In FIG. 6, since the positive and negative output voltage difference between the secondary windings 101 and 102 is used, it goes without saying that the winding ratio should be set so that the rectified output on the winding 102 side is larger. stomach.

[Effects of the Invention] As is clear from the above, the present invention provides a power supply device that supplies direct current and alternating current to high voltage loads such as charging circuits, and direct current to low voltage loads such as control systems and sheet conveyance circuits. An image forming apparatus having a common switching transformer for supplying power to the high-voltage and low-voltage DC loads, and a control means for stopping the high-voltage output of the switching transformer for a period until the output on the low-voltage side stabilizes. This configuration allows low-voltage and high-voltage DC to be supplied from the same switching transformer that is separate from the AC power supply, reducing the number of transformers in the power supply and providing the most suitable for DC output. A transformer for DC output can be driven using transformer drive conditions, such as drive frequency. Further, high voltage output is prohibited during a period when low voltage output supplied to a control system or the like is not stable, thereby preventing adverse effects on high voltage loads such as chargers, photosensitive drums, etc. Therefore, according to the present invention, the configuration of the device can be made simple and inexpensive, efficient power supply conditions suitable for the load can be obtained, and damage to the load can be prevented and stable performance can be achieved over a long period of time.
It has the excellent effect of maintaining

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a power supply unit of an image forming apparatus adopting the present invention, FIG. 2 is a circuit diagram of a drive control circuit of FIG. 1, and FIG. 3 is a circuit diagram showing a modification of the configuration of FIG. 1. 4 to 6 are circuit diagrams showing different configurations of the power supply unit of the image forming apparatus according to the present invention, and FIGS. 7 and 8 are circuit diagrams showing the power supply unit of the conventional image forming apparatus. be. l, 26.27...Transformer drive control circuit 2...Switching transformer 3...5V generation circuit 4...24V generation circuit 8.
21.37.38.42.46...transistor lO
...Operational amplifier 24,25...AC transformer 28...Photosensitive drum 29...Charger 30...Developer 31...
Transfer roller 32...Oscillation circuit 91-95...2
Next winding

Claims (1)

[Claims] 1) In an image forming apparatus that has a power supply device that supplies direct current and alternating current to high voltage loads such as charging circuits, and direct current to low voltage loads such as control systems and sheet conveyance circuits, 1. An image forming apparatus comprising: a common switching transformer for supplying power; and a control means for stopping high-voltage output of the switching transformer for a period until the low-voltage output stabilizes.