JP6727806B2 - Power supply device and image forming apparatus - Google Patents

Description

The present invention relates to a power supply device and an image forming apparatus, and more particularly to a secondary side rectifier circuit of a switching power supply using a transformer.

2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus that copies an image on a recording sheet using an electrophotographic technique has been widely used. The image forming apparatus emits light such as a laser based on image data to a photosensitive drum uniformly charged to a positive or negative high potential, and forms a latent image by electrostatic charge on the photosensitive drum. Then, a developer such as toner is sprayed onto the latent image on the photosensitive drum by electrostatic force to develop on the photosensitive drum. Then, the recording paper is superposed on the developed developer, and a charge having a polarity opposite to that of the charge held by the developer is applied from the back surface of the recording paper, and the developer is attracted and transferred to the surface of the recording paper by electrostatic force. Then, heat and pressure are applied to the recording paper to fix the transferred developer on the recording paper. As described above, in the electrophotographic method, since the developer is moved by using the electrostatic force in each process, a power source that generates various polarities and various high voltages is required.

For example, Patent Document 1 describes details of the image forming apparatus. Since the developer is negatively charged, this image forming apparatus has a positive power source that outputs a positive voltage as a transfer voltage for transferring the developer onto the recording paper. Further, the image forming apparatus of Patent Document 1 has a negative power source for generating a charging voltage for charging the photosensitive drum, a developing voltage for blowing the developer to the photosensitive drum, and a transfer negative voltage for cleaning the transfer roller. These voltages are high voltages of several hundred to several thousand V, and a booster circuit using a transformer or the like is required to generate the high voltage. Therefore, originally, four transformers are required for four voltages of the transfer positive voltage, the transfer negative voltage, the charging voltage, and the developing voltage. For example, in Patent Document 1, a transfer positive voltage is generated by a dedicated transformer for a transfer roller that requires both positive and negative polarities, and the transfer negative voltage is shared with a transformer generating a charging voltage. I am trying. As a result, the booster circuit is composed of three transformers as a whole, and the cost is reduced.

By the way, from the viewpoint of reducing the number of transformers with respect to the number of types of outputs in this way, there is a configuration called a multi-output transformer as a general technique of switching power supplies. The multi-output transformer is a transformer in which one primary winding and a plurality of secondary windings having different numbers of turns are wound around one core, and different voltages can be generated from the respective secondary windings. By reversing the direction of the rectifying element connected to each secondary winding of the multi-output transformer, it is possible to generate voltages with different polarities with a single transformer. It can also be generated with a smaller number of transformers than the number of types.

JP, 2007-206414, A

However, in the case of a multi-output transformer, in order to output a particularly high voltage, the ratio of the number of turns of the primary winding and the secondary winding must be increased, and a plurality of secondary windings are wound on top of it. Then, the total number of turns of the secondary winding increases, resulting in a large transformer. In addition, since the number of turns is adjusted to match the output voltage, it is a dedicated product, and it becomes a transformer with low versatility that cannot respond to changes in output specifications. Further, there is a problem that the fluctuation of the output current of one secondary winding affects the output voltage of the other secondary winding, and the accuracy is low and the control is difficult. Further, the transfer positive voltage, the transfer negative voltage, the charging voltage, and the developing voltage in the conventional example need to be independently changed and turned on or off. Therefore, it is not realistic to use a multi-output transformer that cannot be flexibly controlled as a power source for an image forming apparatus as in the conventional example. In the conventional example, it was possible to reduce the number of transformers by combining some of the transformers that generate a plurality of voltages. However, it is necessary to provide a transformer for positive voltage generation to generate a positive voltage and a transformer for negative voltage generation to generate a negative voltage. For example, one pair of positive voltage and negative voltage is required. If so, at least two transformers were needed.

The present invention has been made under such circumstances, and an object of the present invention is to generate voltages having different polarities with a single transformer without reducing versatility.

In order to solve the problems described above, the present invention has the following configurations.

(1) and one transformer having a primary winding and a secondary winding, Oite the power supply device and a switching element connected to the primary winding of the transformer, the transformer secondary windings One end is connected to ground, the other end is connected to a first line for outputting a positive voltage and a second line for outputting a negative voltage, in the first line A first diode whose anode terminal is connected to the other end of the secondary winding, and a first capacitor which is connected between the cathode terminal side of the first diode and the ground in the first line. A second diode whose cathode terminal is connected to the other end side of the secondary winding in the second line, and a second diode which is connected between the anode terminal side of the second diode and the ground in the second line. A second capacitor, a resistor connected to the cathode terminal side of the first diode in the first line, and a value corresponding to a negative voltage output from the second line and a reference voltage. And a first changing unit that changes the voltage applied to the primary winding of the transformer based on the positive voltage, and the switching based on the comparison result by the comparing unit. A power supply device comprising: a second changing unit that controls the negative voltage by controlling a driving state of an element and changes the reference voltage .

According to the present invention, it is possible to generate voltages having different polarities with one transformer without deteriorating versatility.

Circuit diagram of the power supply device of Embodiment 1 Circuit diagram of the power supply device of Embodiment 2 Circuit diagram of the power supply device of Embodiment 3 Circuit diagram of a power supply device of another embodiment FIG. 6 illustrates an image forming apparatus according to a fourth exemplary embodiment.

Hereinafter, modes for carrying out the present invention will be described in detail with reference to the drawings by embodiments. The power supply device described below is, for example, a power supply that generates various high voltages required in an electrophotographic image forming apparatus. Here, the image forming apparatus includes, for example, a copying machine, a laser printer, an LED printer, an electrophotographic facsimile, and the like.

[Power supply]
FIG. 1 is a circuit diagram of the power supply device according to the first embodiment. The power supply device of FIG. 1 is a switching power supply, and is, for example, a circuit that outputs a positive voltage of +300 V from the output 1 and a negative voltage of −750 V from the output 2. In the circuit of this embodiment, a voltage and a current having different polarities are output from one transformer for a load requiring a positive voltage and a load requiring a negative voltage among a plurality of voltages used in the image forming apparatus. To supply. In particular, it is characterized in that the load fluctuation of one does not affect the voltage generation of the other.

A power source for generating a voltage V1 for generating a primary current flowing through the primary winding 101a of the transformer T101 is connected to the primary side of the power supply device. This V1 is a DC power source for supplying a large electric power, for example, 24V. Is. A power supply for supplying a voltage V2 to the control circuit is connected to the primary side of the power supply device, and this V2 is a highly accurate DC power supply for supplying 3.3V, 5V or the like.

The transformer T101 is a transformer having a primary winding 101a and a secondary winding 101b, and its winding ratio is, for example, 84:2700 for boosting. A Q101 which is a switching element for performing a switching operation is connected to one end of the primary winding 101a of the transformer T101. A MOSFET is used as the switching element Q101. The gate terminal of the switching element Q101 is connected to the input 1 to which a signal from the control unit of the device in which the power supply device is mounted is input, and the signal input to the input 1 turns on/off the switching element Q101, that is, The switching operation (oscillation operation) is controlled. A resistor R102 is connected between the gate terminal and the source terminal of the switching element Q101.

The cathode terminal of the diode D103 is connected to the other end of the primary winding 101a of the transformer T101, and the anode terminal of the diode D103 is connected to the ground (hereinafter, GND). The primary winding 101a of the transformer T101 has an intermediate tap, and a capacitor C104 is connected between the tapped portion of the primary winding 101a and the anode terminal of the diode D103. Further, the voltage V1 is supplied to the tapped portion of the transformer T101 via the resistor R107. The current flowing through the primary winding 101a of the transformer T101 flows in the order of V1→R107→T101→Q101 when the switching element Q101 is on, and flows in the order of T101→C104→D103 when the switching element Q101 is off. The current flowing when the switching element Q101 is off is a regenerative current. In this embodiment, the primary winding 101a of the transformer T101 is tapped, but the configuration is not limited to this.

The secondary winding 101b of the transformer T101 is connected to a first line for outputting a positive voltage and a second line for outputting a negative voltage. Specifically, the anode terminal of the diode D101 and the cathode terminal of the diode D102 are connected to one end of the secondary winding 101b. That is, the diode D101 and the diode D102 in which the polarities of the diodes are differently connected are both connected to one end of the secondary winding 101b of the transformer T101. The diode D101 is a first rectifying element that is connected to the secondary winding 101b of the transformer T101 in a predetermined direction and outputs a positive polarity voltage that is a voltage of the first polarity. The diode D102 is connected to the secondary winding 101b of the transformer T101 in parallel with the diode D101 in a direction opposite to the predetermined direction, and outputs a negative voltage having a second polarity opposite to the first polarity. Is a second rectifying element for.

One end of a capacitor C102 is connected to the cathode terminal of the diode D101, and the other end of the capacitor C102 is connected to GND. Further, the cathode terminal of the diode D101 is connected to the cathode terminal of the Zener diode ZD101 via the resistor R106, and is supplied to the load as the output 1 of the power supply device. The anode terminal of the Zener diode ZD101 is connected to GND. Further, one end of a capacitor C103 is connected to the anode terminal of the diode D102 and is supplied to the load as the output 2 of the power supply device. The other end of the capacitor C103 is connected to GND. The other end of the secondary winding 101b of the transformer T101 is connected to GND.

As the operation of the secondary side of the transformer T101, when the switching element Q101 is on, the diode D101 turns on and the diode D102 turns off. On the secondary side of the transformer T101, current flows in the order of T101→D101→C102. The capacitor C102 is charged with a positive voltage with respect to GND. On the other hand, when the switching element Q101 is off, the diode D101 is off and the diode D102 is on. A current flows through the secondary side of the transformer T101 in the order of GND→C103→D102→T101. The capacitor C103 is charged with a negative voltage with respect to GND. This is because the diode D101 and the diode D102 are connected in opposite directions (polarity), so that the diode D101 conducts by the forward operation of the transformer T101 and the diode D102 conducts by the flyback operation of the transformer T101. ..

Then, the voltage (positive) charged in the capacitor C102 flows into the GND through the resistor R106 and the Zener diode ZD101. The Zener diode ZD101 has a Zener voltage of 300V. Therefore, the output 1 is
(C102 voltage−(R106 resistance value×R106 current))>300
As long as the condition is satisfied, the predetermined voltage of 300 V is continuously maintained. As described above, the Zener diode ZD101 is a constant voltage element that is connected to the output side of the diode D101 and maintains the voltage of the output 1 at a predetermined voltage determined by the Zener voltage.

(Feedback control of output 2)
On the other hand, feedback control is performed on the output 2. The comparator CP101 is a comparison unit (comparison unit) that compares the voltage corresponding to the voltage output from the output 2 with the reference voltage, and the switching element Q101 is controlled based on the comparison result by the comparator CP101.

The output 2 is connected to one end of the resistor R105, and the other end of the resistor R105 is connected to one end of the resistor R104. The other end of the resistor R104 is connected to a power supply that supplies the voltage V2. The connection point between the resistors R104 and R105 is connected to the non-inverting input terminal of the comparator CP101. That is, the voltage obtained by dividing the difference between the voltage V2 and the voltage of the output 2 by the resistors R104 and R105 is input to the non-inverting input terminal of the comparator CP101. Further, one end of the resistor R103 is connected to the power supply that supplies the voltage V2, and the other end of the resistor R103 is connected to one end of the resistor R108. The other end of the resistor R108 is input to the inverting input terminal of the comparator CP101. The other end of the resistor R108 is connected to one end of the capacitor C101, and the other end of the capacitor C101 is connected to GND. The resistor R108 and the capacitor C101 form an integrating circuit. Further, a signal is input from the input 2 to the inverting input terminal of the comparator CP101. The output terminal of the comparator CP101 is connected to the gate terminal of the switching element Q101.

The mechanism of feedback control of the output 2 will be described below. A clock pulse for driving the switching element Q101 is input from the input 1 via the resistor R101. For example, the signal input to the input 1 is a signal having a frequency of 16.6 kHz and an on-duty of 10% and 3.3 Vpp, and is input from an oscillation circuit (not shown) or a CPU, which is a control unit (not shown). .. The oscillator circuit and the control unit may be included in the power supply device or may be included in a device in which the power supply device is mounted. An image forming apparatus or the like is an example of a device in which the power supply device is mounted.

A PWM (Pulse Width Modulation) signal for determining the output voltage of the output 2 is input to the input 2. A transistor, a general-purpose port of a CPU having an open drain structure, or the like is connected to the input 2 at a portion (not shown), and a binary PWM signal of high impedance (High-Z) and low level (Low) is input. For example, when the PWM signal input to the input 2 is 100% off-duty (high impedance state), the output voltage of the output 2 is -1500V. With this configuration, when the off-duty of the PWM signal input to the input 2 is 50%, the voltage of the output 2 becomes −750V. The CPU or the like connected to the input 2 functions as a changing unit (changing unit) that changes the voltage input to the inverting input terminal of the comparator CP101.

[Power supply operation]
A specific operation will be described. When the PWM signal is input from the input 2, a voltage equal to or lower than the voltage V2 is input to the inverting input terminal of the comparator CP101 according to the duty of the PWM signal. A voltage obtained by dividing the difference between the voltage of the voltage V2 and the voltage of the output 2 by the resistors R104 and R105 is input to the non-inverting input terminal of the comparator CP101. The comparator CP101 compares the voltages input to the inverting input terminal and the non-inverting input terminal. Here, the voltage input to the inverting input terminal of the comparator CP101 is a voltage that becomes a target value of the output voltage of the output 2 (hereinafter, target voltage) and is a reference voltage. As described above, the target voltage can be changed by changing the duty of the PWM signal input from the input 2.

On the other hand, the voltage input to the non-inverting input terminal of the comparator CP101 is the feedback voltage of the output 2. The comparator CP101 outputs a low level signal when the target voltage input to the inverting input terminal is higher than the feedback voltage input to the non-inverting input terminal, and the signal of the input 1 input to the gate terminal of the switching element Q101. Pull in. Therefore, no voltage is applied to the gate terminal of the switching element Q101 while the signal output from the comparator CP101 is at low level. Therefore, the oscillation operation of the switching element Q101 by the signal (clock pulse) input from the input 1 to the gate terminal of the switching element Q101 is stopped.

An example is given using specific numerical values. A pulse signal having a frequency of 16.6 kHz and a high duty of 10% is selected as a signal input to the input 1, and a PWM signal having a frequency of 32 kHz and an off duty of 50% is selected as a signal input to the input 2. Further, constants are selected so that the voltage V2 is 5.4 V and the ratio of the resistors R104 and R105 is 4:1119. Then, the voltage input to the inverting input terminal of the comparator CP101 becomes
5.4×0.5=2.7 (V)
Becomes When the voltage of the output 2 is 0V, the voltage input to the non-inverting input terminal of the comparator CP101 is
5.4-((5.4-0)×(4/1123))=5.38 (V)
Is. At this time, the relationship between the voltages input to the terminals of the comparator CP101 is
Non-inverting input terminal (5.38V)> inverting input terminal (2.7V)
Therefore, the output of the comparator CP101 becomes high impedance, and the signal of the input 1 drives the switching element Q101 without being masked by the output of the comparator CP101. As the switching element Q101 is driven, the voltage of the output 2 drops with respect to GND.

When the voltage of the output 2 becomes −750V, the voltage input to the non-inverting input terminal of the comparator CP101 is
5.4-(5.4-(-750))*(4/1123)=2.7(V)
Becomes Furthermore, when the switching element Q101 continues to oscillate, the voltage of the output 2 decreases, and the relationship between the voltages input to the terminals of the comparator CP101 is:
Non-inverting input terminal <inverting input terminal. Therefore, the comparator CP101 outputs a low level signal. When the output of the comparator CP101 becomes low level, the pulse signal input from the input 1 is drawn into the output terminal side of the comparator CP101, and the switching element Q101 cannot be driven. In this way, the output 2 on the secondary side of the transformer T101 is determined by the duty of the PWM signal input from the input 2. Further, the comparator CP101 appropriately controls the voltage of the output 2 even if the load connected to the output 2 changes.

As described above, according to the present embodiment, it is possible to generate voltages having different polarities with one transformer, with almost no deterioration in versatility. In particular, as a single transformer, a general-purpose transformer can be used instead of a dedicated transformer such as a multi-output transformer, and the positive and negative outputs obtained are highly accurate and stable with almost no interference with each other. It can be used as a power source.

[Power supply]
FIG. 2 is a circuit diagram showing the configuration of the power supply device according to the second embodiment. The same components as those in FIG. 1 described in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the configuration of the output 2 side on the secondary side of the power supply device is different from that of the first embodiment. In this embodiment, one end of the resistor R201 is connected to the secondary winding 101b of the transformer T101, and the other end of the resistor R201 is connected to one end of the capacitor C202. The other end of the capacitor C202 is connected to the cathode terminal of the diode D201. The other end of the capacitor C202 is also connected to the anode terminal of the diode D202. The anode terminal of the diode D201 is connected to one end of the capacitor C201. The cathode terminal of the diode D202 is connected to the other end of the capacitor C201, and its connection point is connected to GND.

In the first embodiment, the flyback voltage generated on the secondary side of the transformer T101 is rectified and used as it is as the output 2. In this embodiment, a voltage doubler rectifier circuit including a diode D201, which is a second rectifier, and composed of a diode D202 and capacitors C201 and C202 is formed to provide an output 2. Note that the configuration of the voltage doubler rectifier circuit that rectifies the voltage induced in the secondary winding 101b of the transformer T101 into a voltage doubler is a general technique, and a description thereof will be omitted. In this embodiment, the voltage doubler rectifier circuit is provided, so that the voltage generated as the output 2 becomes higher than that of the power supply device of the first embodiment. Examples will be given using specific numerical values. In the first embodiment, when the PWM signal of the input 2 has a duty of 100%, the voltage of the output 2 is -1500V. On the other hand, in this embodiment, when the PWM signal of the input 2 has a duty of 100%, the voltage of the output 2 can generate a voltage having a potential lower than -1500V.

The first embodiment is configured so that the load fluctuations of the output 1 and the output 2 have almost no influence on each other. However, the range of load fluctuation is limited. Specifically, when the load of the output 2 becomes light, the current supply capacity of the output 1 may decrease, and the voltage of the output 1 may decrease. This is because the output 1 and the output 2 share the transformer T101, and the period in which the transformer T101 is excited, that is, the driving frequency of the switching element Q101 is performed by the feedback of the output 2. Therefore, when the output 2 becomes a light load, the excitation frequency of the transformer T101 decreases, and the current supply to the output 1 using the forward output of the transformer T101 also decreases. In this embodiment, the resistance R201 is provided between the secondary winding 101b of the transformer T101 and the voltage doubler rectifier circuit in order to cope with the case where the output 2 has a light load as described above.

(Function of resistor R201)
When the resistor R201 is connected to the secondary winding 101b of the transformer T101, the voltage drops due to the resistor R201, and it becomes difficult to increase the charging voltage of the capacitor C201 due to the flyback voltage of the transformer T101. Therefore, the resistor R201 functions as a voltage drop means. For example, when the resistance value of the resistor R201 is 0Ω, that is, when the resistor R201 is not connected, and the excitation frequency of the transformer T101 is A, the charging voltage of the capacitor C201 is B. When the resistance value of the resistor R201 is 100 kΩ, the charging voltage of the capacitor C201 is C when the transformer T101 has the same excitation frequency A. Then, the charging voltage C of the capacitor C201 becomes lower than the charging voltage B. In other words, when trying to output a predetermined voltage to the output 2, the excitation frequency of the transformer T101 is higher when the resistor R201 is connected than when the resistor R201 is not connected. Means that it must be frequency. From the above, by connecting the resistor R201 to the secondary side of the transformer T101, even if the load of the output 2 becomes light, the excitation frequency of the transformer T101 is driven at a high frequency. As a result, it is possible to maintain a state in which the current supply capacity for the load of the output 1 is high.

The value of the resistor R201 satisfies the condition that the voltage drop of the output 1 does not occur at the lightest load assumed for the load connected to the output 2 and at the heaviest load assumed for the output 1. The value is set. Moreover, the maximum output capability of the output 2 is reduced by connecting the resistor R201. Therefore, it is necessary to confirm whether the predetermined voltage can be supplied to the heaviest load assumed for the output 2 with the constant set for the resistance value of the resistor R201.

By the way, by using the above-described principle, it is possible to solve the problem that occurs when the load of the output 2 becomes a light load, even with a configuration in which a resistor or the like is connected as a pseudo load between the output 2 and the GND. Is. The reason why the resistor R201 is connected to the illustrated position in this embodiment is that this embodiment employs a voltage doubler rectifier circuit and can output a higher output voltage than that in the first embodiment. Therefore, in this embodiment, the resistor R201 is connected to the front stage (upstream side) of the voltage doubler rectifier circuit. If -3000V is output as the voltage of the output 2, and if a resistor or the like is connected as the pseudo load to the output 2 portion, the resistance connected as the pseudo load needs a component having a withstand voltage of 3000V or more. A resistor having a high withstand voltage has a large area and a high cost. On the other hand, when the voltage doubler rectifier circuit is provided as in this embodiment, the resistor R201 is connected to the input side of the voltage doubler rectifier circuit. Therefore, it is possible to use a component having a breakdown voltage of 1500 V or less, which is half of 3000 V, and a component having a relatively small area and a low cost can be used.

As described above, according to the present embodiment, it is possible to generate voltages having different polarities with one transformer without substantially reducing versatility.

FIG. 3 is a circuit diagram showing the configuration of the power supply circuit according to the third embodiment. The same components as those described in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the present embodiment, the transistor Q301 is connected between the power source for generating the voltage V1 on the primary side of the transformer T101 and the capacitor C104. More specifically, the voltage V1 is supplied to the emitter terminal of the transistor Q301, and one end of the capacitor C104 is connected to the collector terminal of the transistor Q301. The signal from the input 3 is connected to the base terminal of the transistor Q301 via the resistor R304. A resistor R303 is connected between the base terminal and the emitter terminal of the transistor Q301. Further, in this embodiment, one end of the resistor R302 is connected between the cathode terminal of the diode D101 on the secondary side of the transformer T101 and the output 1, and one end of the resistor R301 is connected to the other end of the resistor R302. There is. The other end of the resistor R301 is connected to GND, and the connection point of the resistors R301 and R302 is connected to the output 3.

In the first and second embodiments, the output 1 is controlled to a constant voltage by the Zener diode ZD101. On the other hand, in this embodiment, the output voltage of the output 1 is variable. As shown in FIG. 3, the voltage of the output 3 which is a voltage obtained by dividing the output voltage of the output 1 by the resistors R301 and R302 is fed back to a control circuit such as a CPU (not shown). On the other hand, the primary side of the transformer T101 directly supplies the voltage V1 from the power source in the first and second embodiments, but in the present embodiment, the voltage applied to the transformer T101 is variable by the transistor Q301. The transistor Q301 functions as a control unit that controls the voltage of the output 1, and also functions as a changing unit that changes the voltage applied to the primary winding 101a of the transformer T101. For example, the input 3 is connected to a D/A converter or a drive circuit controlled by a control circuit such as a CPU (not shown). Then, the voltage between the emitter terminal and the collector terminal of the transistor Q301 may be controlled based on the voltage of the output 3 obtained by dividing the voltage of the output 1 so that the voltage of the output 1 becomes a predetermined voltage.

For example, if the output voltage of output 1 is higher than a predetermined value, the voltage obtained from output 3 will also be high. In this case, the control circuit to which the output 3 is input reduces the current drawn from the input 3 and increases the potential difference between the collector terminal and the emitter terminal of the transistor Q301. This reduces the voltage supplied to the transformer T101. When the voltage supplied to the transformer T101 decreases, the exciting current of the transformer T101 decreases, and the voltage of the output 1 generated by the forward voltage of the transformer T101 decreases.

On the other hand, when the output voltage of the output 1 is lower than the predetermined value, the voltage obtained from the output 3 is also low. In this case, the control circuit to which the output 3 is input increases the current drawn from the input 3 to reduce the potential difference between the collector terminal and the emitter terminal of the transistor Q301. This increases the voltage supplied to the transformer T101. When the voltage supplied to the transformer T101 increases, the exciting current of the transformer T101 increases, and the voltage of the output 1 generated by the forward voltage of the transformer T101 increases. In this way, the output 1 is controlled to a constant voltage by repeating these operations.

At this time, if the voltage supplied to the transformer T101 changes, the flyback voltage of the transformer T101 also changes, so that when the switching element Q101 is driven at a constant frequency, the output voltage of the output 2 is also affected. .. However, as described above, the output voltage of the output 2 is automatically controlled so as to be the target voltage designated by the input 2 by the comparator CP101. Therefore, the output voltage of the output 2 can maintain a predetermined voltage. In this way, it is possible to control the outputs 1 and 2 having different polarities so as to have predetermined voltages, respectively, with one transformer. The predetermined voltage is a value determined by the control circuit or the like. The configuration of the output 1 of the present embodiment may be applied to the configuration of the output 1 of the second embodiment.

As described above, according to the present embodiment, it is possible to generate voltages having different polarities with one transformer without substantially reducing versatility.

(Other embodiments)
In the power supply devices of Examples 1 to 3 described above, the configuration using the electromagnetic transformer including the primary winding and the secondary winding has been described, but the configuration is not limited to the electromagnetic transformer and may be configured using a piezoelectric transformer, for example. It is possible.

FIG. 4 shows a configuration using a piezoelectric transformer. The same components as those described with reference to FIG. 1 and the like are designated by the same reference numerals and the description thereof will be omitted. The power supply device of FIG. 4 includes a piezoelectric transformer P101 (piezoelectric ceramic transformer). As the AC output of the piezoelectric transformer P101, positive and negative voltages (outputs 1 and 2) are output by the circuit configuration similar to that of the first embodiment. The negative output voltage (output 2) is divided by the resistors 105, 106 and 107 and input to the non-inverting input terminal (+ terminal) of the operational amplifier 109 via the protection resistor 108. On the other hand, the control signal (Vcont) of the high-voltage power supply, which is an analog signal, is input to the connection terminal 118 from the DC controller (not shown) to the inverting input terminal (− terminal) of the operational amplifier 109 via the resistor 114.

The operational amplifier 109, the resistor 114, and the capacitor 113 are connected as shown in FIG. 4 to form an integrating circuit. As a result, the control signal Vcont smoothed by the integration time constant determined by the constants of the resistor 114 and the capacitor 113 is input to the operational amplifier 109. The output terminal of the operational amplifier 109 is connected to a voltage controlled oscillator (hereinafter referred to as VCO) 110. The output terminal of the VCO 110 is connected to the base terminal of the transistor 111 whose collector terminal is connected to the inductor 112, and by driving the transistor 111, the power supply voltage (+24 V) is supplied to the primary side of the piezoelectric transformer P101.

In addition, in the configuration using the piezoelectric transformer P101 of the present embodiment, the AC output may be the circuit configuration described in the second embodiment (FIG. 2) and the third embodiment (FIG. 3).
As described above, according to the other embodiments, the same effects as those of the first to third embodiments can be obtained even in the configuration using the piezoelectric transformer.

The power supply device described in the above embodiments can be applied as a power supply for an image forming apparatus, for example. The configuration of the image forming apparatus to which the power supply devices of the above-described embodiments are applied will be described below.

[Configuration of image forming apparatus]
A laser beam printer will be described as an example of the image forming apparatus. FIG. 5 shows a schematic configuration of a laser beam printer which is an example of an electrophotographic printer. The laser beam printer 300 includes a photosensitive drum 311 as an image carrier on which an electrostatic latent image is formed, a charging unit 317 (charging means) that uniformly charges the photosensitive drum 311, and an electrostatic latent image formed on the photosensitive drum 311. A developing unit 312 (developing unit) that develops an image with toner is provided. Then, the toner image developed on the photosensitive drum 311 is transferred to a sheet (not shown) as a recording material supplied from the cassette 316 by a transfer unit 318 (transfer means), and the toner image transferred to the sheet is fixed by a fixing device ( The image is fixed by the fixing unit) 314 and discharged onto the tray 315. The photosensitive drum 311, the charging unit 317, the developing unit 312, and the transfer unit 318 are image forming units. The laser beam printer 300 also includes the power supply device 400 described in the first to third embodiments. The image forming apparatus to which the power supply device 400 according to the first to third embodiments is applicable is not limited to the one illustrated in FIG. 5, and may be an image forming apparatus including a plurality of image forming units, for example. Further, the image forming apparatus may include a primary transfer unit that transfers the toner image on the photosensitive drum 311 to the intermediate transfer belt and a secondary transfer unit that transfers the toner image on the intermediate transfer belt to the sheet.

The laser beam printer 300 includes a controller 320 that controls an image forming operation by the image forming unit and a sheet conveying operation. In the laser beam printer 300 including the power supply device according to the first and second embodiments, the controller 320 outputs the pulse signal for performing the switching operation of the switching element Q101 to the input 1 of the power supply device 400. Further, the controller 320 outputs, to the input 2 of the power supply device 400, a PWM signal for controlling the output voltage from the output 2 to a predetermined voltage. The power supply device 400 outputs a positive voltage from the output 1 to a member of the laser beam printer 300 that requires a positive voltage. Further, the power supply device 400 outputs the negative voltage from the output 2 to the member of the laser beam printer 300 that requires the negative voltage. For example, the power supply device 400 outputs the negative voltage required for cleaning to the transfer unit 318 and the charging voltage to the charging unit 317 from the output 2.

Further, in the laser beam printer 300 including the power supply device of the third embodiment, the controller 320 controls the voltage output from the output 1 to a predetermined voltage based on the signal input from the output 3 of the power supply device 400. , Outputs a signal to the input 3 of the power supply device 400.

As described above, according to the present embodiment, it is possible to generate voltages having different polarities with one transformer without substantially reducing versatility.

C102 capacitor C201 capacitor CP101 comparator D101 diode D102 diode Q101 FET
R106 resistor T101 transformer

Claims (3)

Oite the power supply device comprising: a single transformer, and a switching element connected to the primary winding of the transformer having a primary winding and a secondary winding,
The secondary winding of the transformer has one end connected to the ground, and the other end connected to a first line for outputting a positive voltage and a second line for outputting a negative voltage. Cage,
A first diode whose anode terminal is connected to the other end of the secondary winding in the first line,
In the first line, a first capacitor connected between the cathode terminal side of the first diode and the ground,
A second diode whose cathode terminal is connected to the other end of the secondary winding in the second line,
A second capacitor connected between the anode terminal side of the second diode and the ground in the second line,
A resistor connected to the cathode terminal side of the first diode in the first line,
A comparison unit that compares a value according to the negative voltage output from the second line with a reference voltage,
A first changing unit that changes a voltage applied to the primary winding of the transformer based on the positive voltage;
Have
Based on the comparison result by the comparison unit, the negative voltage is controlled by controlling the driving state of the switching element,
A power supply device comprising a second changing unit that changes the reference voltage. The power supply device according to claim 1, further comprising a rectifier circuit that includes the second diode and rectifies a voltage induced in the secondary winding of the transformer into a voltage doubler. The power supply device according to claim 1 or 2, further comprising a constant voltage element connected to the cathode terminal side of the first diode, for maintaining the positive voltage at a constant voltage. ..

Images