JPH01202166A - Power source - Google Patents

Abstract

PURPOSE:To reduce the size and weight of a power source by connecting the outputs of the secondary side positive and negative rectifying and smoothing circuit of a switching transformer, and switching the polarity of a load supply voltage by the opening/closing of a semiconductor switch. CONSTITUTION:An electrophotographic type image forming apparatus uniformly charges a photosensitive drum 1 by a charger 2 at the time of forming an image, thereby forming an electrostatic latent image on the drum. The latent image is transferred by a developer 4 and a transfer roller 3. This power source system is supplied from a commercial AC power source 45, a switching transistor(Tr) 40, a diode 41 and a resonance capacitor 42 provided in parallel are inserted between a capacitor 43 connected through a rectifier 44 and the primary winding of a switching transformer 5 to be driven. The secondary winding 6 of the transformer 5 supplies positive/negative output to the roller 3. Since the output is controlled in its polarity by resistors 16-17, a Tr 18, the reliability of the power source is enhanced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a power supply device, in particular, a power supply device, in particular, a power supply device that uses an alternating current generated in the secondary winding of a switching transformer by intermittent direct current applied to the primary winding of the switching transformer. The present invention relates to a power supply device that rectifies both positive and negative polarities and switches the positive or negative voltage to supply it to a predetermined load.

[Prior Art] Conventionally, electrophotographic image forming apparatuses such as copying machines and laser beam printers have sometimes required a power supply device capable of outputting high voltages of both positive and negative polarities. In such cases, the following method is usually used.

For example, as shown in FIG. 5, two power supply devices with different polarities each consisting of a drive circuit 81, 82, a switching transformer 83, 84, a rectifying and smoothing circuit 85, 86 with different polarities each consisting of a diode, and a capacitor are connected to a load resistor. For example, 1000V, t3J:
There is a structure in which a 00V (7) output is fed to a load 90 via a resistor 89. In this structure, the transformer drive circuit 81,
By operating either of 82, either positive or negative voltage can be supplied to load 90.

Alternatively, as shown in FIG. 6, there is a method in which the outputs of two power supply systems configured in the same manner as in FIG. 5 are selected using a high voltage relay 91 to supply power to a load 90.

Furthermore, if the polarity of the power supplied to the same load changes depending on the use of the device, a method of replacing the power supply section may be considered.

[Problems to be Solved by the Invention] However, in the structure shown in FIGS. 5 and 6, independent transformer drive circuits and transformers are required for the two power sources, which increases the size and weight of the device. There is a problem that the number of people is also increasing. In addition, the method shown in Figure 6 requires the use of expensive high-voltage relays, and it is difficult to maintain the reliability of the relay contacts over a long period of time, making it difficult to perform stable operation. . Another problem with the system of replacing the power supply is that it forces the user to perform troublesome work.

The present invention aims to solve such problems.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, the direct current generated in the secondary winding of the switching transformer is generated by intermittent direct current applied to the primary winding of the switching transformer. In a power supply device that rectifies alternating current with both positive and negative polarities and switches this positive or negative voltage to supply a predetermined load, the positive and negative rectifiers are connected to at least one secondary winding of the switching transformer. A smoothing circuit, a resistor network connecting the outputs of these positive and negative rectifying and smoothing circuits in parallel, and a semiconductor switch connected between a predetermined point in this resistor network and ground potential are provided, and by opening and closing of this semiconductor switch, A configuration is adopted in which the polarity of the voltage supplied to the load from a predetermined point of the resistor network is switched.

[Operation] According to the above configuration, a positive or negative voltage can be supplied to a predetermined load from a common switching transformer without using a plurality of switching transformers.

[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 system of an electrophotographic image forming apparatus employing the present invention. In FIG. , during the formation of a zero image that undergoes each image forming process, the photosensitive drum 1 is first uniformly charged by the charger 2 . Subsequently, the drum is irradiated with light such as reflected light from the original or a modulated laser beam, and an electrostatic latent image is formed on the drum. Subsequently, this electrostatic latent image is developed with toner by a developing device 4, and further transferred to a recording medium such as paper by a transfer roller 3.

The above charger 2 and developer 4 each require a predetermined high voltage of -. Further, for the transfer roller 3, high pressure of either positive or negative polarity is required depending on the image forming conditions. These supplies are provided by the circuit on the left side of the diagram.

Power for the device is supplied from a commercial AC power source 45. The output of the commercial AC power supply 45 is directly rectified by the rectifier circuit 44 and input to the capacitor 43 . The primary winding of the switching transformer 5 for voltage conversion is driven by the direct current appearing across the capacitor 43. That is, a switching transistor 4o and a diode 41 are connected in parallel between the capacitor 43 and the primary winding of the switching transformer 5.
A resonance capacitor 42 is inserted, and a control IC 46 applies a driving pulse to the switching transistor 40 to control the switching transformer 5.
Drives the primary side of.

The switching transformer 5 is provided with three secondary windings indicated by symbols 6 to 8. The secondary winding 8 is a flyback low voltage winding that generates an output of 24V, and this output is rectified by a diode 22 and a capacitor 24, and is supplied to transformer drive circuits 26 and 27, respectively. Further, the secondary winding 7 is a forward winding for generating a power supply for sequence control, for example, 5V, and its output is supplied to the control circuit via a diode 23 and a capacitor 25. The secondary winding 6 is a flyback winding for feeding power to the transfer roller 3, and the secondary side circuit of this @ wire will be described later.

The 24V DC output from the secondary winding 8 is transmitted to the switching transformer 28.28 via the transformer drive circuit 26.28.
29. The transformer drive circuits 26 and 27 are constituted by a switching circuit similar to the primary side of the switching transformer 5. High-voltage alternating current is output to the secondary sides of the switching transformers 28 and 29, each boosted according to the winding ratio. This alternating current is supplied to the developing device 4 and the charger 2 through filter circuits each composed of resistors 34 to 37 and capacitors 38 and 39.

Note that a predetermined bias voltage (direct current) is applied between these high voltage alternating currents and the ground potential by bias circuits 32 and 33 connected through diodes 30 and 31.

Note that the output of the secondary winding 8 of the switching transformer 5 is detected via a voltage detection circuit 48 composed of a detection resistor, etc., and this detected value is used for controlling the primary side of the switching transformer 5 via a photocoupler 47. It is fed back to IC46. As a result, the switching transformer 5
is controlled by constant voltage output.

The secondary winding 6 of the switching transformer 5 supplies positive or negative output to the transfer roller 3. One end of the secondary winding 6 is grounded, and a diode 9.1 is connected to the other end.
0 anode and cathode are connected. A capacitor 11.12 is connected between the cathode and anode of the diode 9.1o and the ground potential, respectively.

This configuration produces negative and positive output voltages V- and V+ across respective capacitors 11.12. A resistor 13.14 is connected in parallel to the capacitor 11.12, and the output voltage V-1.+ is applied to both ends of the resistor 17 (7) via a resistor 15.16. Resistance 16.17
The collector of the transistor 18 is connected to the connection point. The emitter of the transistor 18 is grounded Pa, and its base is controlled via a terminal 19 by a control circuit (not shown).

Regarding the secondary winding &I6, the output voltage V- rectified by the diode 9 is a forward mode negative voltage, and the diode 10 outputs V+ is a flyback positive voltage. By controlling the switching transformer 5 as a voltage resonance type switching regulator, the above output voltages V+ and V- satisfy 1V+1>1v-1. If the transistor 18 is conductive, the transfer roller 3
The voltage supplied to R1'5+ is R1'5+ when transistor 18 is cut off.
It becomes R1B+R17. Therefore, based on the above two formulas, the resistance 15 to 17
By appropriately setting the value of , the polarity of the voltage supplied to the transfer roller 3 can be reversed by controlling the transistor 18 .

According to the above configuration, unlike the conventional examples shown in FIGS. 5 and 6, the positive or negative voltage applied to the transfer roller as a load can be supplied from the common switching transformer 5. Therefore, the configuration of the power supply section can be simplified and the number of transformers can be reduced, making it possible to make the device smaller and lighter. Also.

Since the polarity can be controlled using a resistor network and a switching transistor without using elements with reliability problems such as relays, the reliability of the device can be improved.

In the above embodiment, the positive or negative voltage supplied to the transfer roller 3 was generated from one secondary winding 6 of the switching transformer 5, but as shown in FIG. 49.50, by which a positive or negative component may be supplied; a secondary winding 49.5;
Similarly to FIG. 1, rectifying diodes 9 and 9.
1o, a capacitor 11.12, and a resistor 13.14 are connected. The + side of each rectified output is transistor 1
8 collector. At this time, a high resistance resistor 51 is connected between the + side output terminal and the collector of the transistor 18.
is inserted. The common line of the secondary winding 50 is grounded.

According to the above configuration, when the transistor 18 is conductive, the negative voltage V- output from the secondary winding 49 is supplied to the transfer roller 3. Output V+ flows to ground potential via resistor 51. When the transistor 18 is turned off, both output voltages V+ and - are supplied via the resistor 51, so that the difference between these voltages is supplied to the transfer roller 3. At this time, a desired voltage can be supplied to the transfer roller 3 by appropriately setting the voltage difference between the secondary windings 49 and 50 depending on the turn ratio of the secondary windings 49 and 50. Even with such a configuration, the same effects as described above can be obtained by only adding one secondary winding.

Further, as an output circuit for the transfer roller 3, a structure as shown in FIGS. 3 and 4 can also be considered. 7 In the configuration shown in FIG. 3, a rectification and smoothing circuit comprising a diode 9, a capacitor 11, and a resistor 13 is connected to the output of the secondary winding 6 similar to that in FIG.

At the same time, the AC output of the secondary winding 6 is connected to the resistor 58, 59 and the transistor 18 through a capacitor that allows only AC to pass through.
is supplied to the series connected circuit. The output of the diode 9 is supplied via the resistor 56 to the connection point between the resistors 58 and 59. The voltage (alternating current) generated across the resistor 58 is rectified and smoothed by the diode 57 and the capacitor 60.

A resistor 61 is connected in parallel to the capacitor 60.
One end of the transfer roller 1 is connected to the transfer roller 3, and the other end is grounded via a capacitor 62. In such a structure, the output of diode 9 is a positive flyback voltage Vl.

At this time, assuming that the forward output is v2, the voltage supplied to the transfer roller 3 will be Vl-V2 when the transistor 18 is cut off and held. Further, when the transistor 18 is conductive, the forward voltage becomes -v2.

In this way, even in the configuration shown in FIG. 3, the forward voltage,
By appropriately setting the flyback voltage through switching control, a voltage of a desired polarity can be supplied to the transfer roller 3.

In addition, in FIG. 4, the diode 9 and capacitor 1 in FIG.
A rectifying and smoothing circuit according to 1 is connected to a capacitor 64 for cutting off DC current,
Dio-F52,63. This is changed to a voltage doubler rectifier circuit using a capacitor 53.

In such a configuration, the flyback voltage and the forward voltage may be the same, that is, it is possible to supply an output of positive or negative polarity to the transfer roller 3 without using a voltage resonance type switching regulator. In the case of Figure 4,
If the peak value of the output of the secondary winding 6 is Va, the output voltage across the capacitor 53 is 2Va, and when the transistor 18 is cut off, the transfer roller 3 receives Va /
2 and -V when transistor 18 is on.
A voltage of a/2 is output.

The above configuration also allows the polarity of the voltage supplied to the load to be reversed.

[Effects of the Invention] As is clear from the above, according to the present invention, by intermittent direct current applied to the primary winding of the switching transformer, the alternating current generated in the secondary winding of the switching transformer can be divided into positive and negative. In a power supply device that rectifies the bipolar voltage and switches the positive or negative voltage to supply it to a predetermined load, a positive and negative rectifying and smoothing circuit connected to at least one secondary winding of the switching transformer; a resistor network connecting the outputs of the positive and negative rectifying and smoothing circuits in parallel;
A semiconductor switch is provided between a predetermined point in the resistor network and ground potential, and the polarity of the voltage supplied from the predetermined point in the resistor network to the load is switched by opening and closing the semiconductor switch. , positive or negative voltage can be supplied to a given load from a common switching transformer without using multiple switching transformers, making it possible to reduce the size and weight of the power supply section. Since switching can be performed, it has excellent advantages such as improving the reliability of the circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a power supply system of an image forming apparatus adopting the present invention, FIGS. 2 to 4 are circuit diagrams showing modifications of FIG. 1, and FIGS. 5 and 6 are conventional circuit diagrams. FIG. 2 is a circuit diagram showing a power supply device of FIG. l...Photosensitive drum 2...Charger 3...Transfer roller 4...Developer 5...Switching transformer 6-8.49.50...Secondary winding 9.10.57. ...Diode 13-17.58.59.6o, 61 ...Resistance 18
...The colloquial expression of transistor 1 is shown in Fig. 5.

Claims (1)

[Claims] 1) By intermittent direct current applied to the primary winding of the switching transformer, the alternating current generated in the secondary winding of the switching transformer is rectified in both positive and negative polarities, and this positive or negative voltage is switched to a predetermined value. In the power supply device for supplying to a load, at least one of the switching transformers
A positive and negative rectifying and smoothing circuit connected to two secondary windings, a resistor network connecting the outputs of these positive and negative rectifying and smoothing circuits in parallel, and a connection between a predetermined point in this resistor network and ground potential. A power supply device comprising: a connected semiconductor switch; opening and closing the semiconductor switch switches the polarity of the voltage supplied to the load from a predetermined point of the resistor network;