JP2007011087A - Power supply device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply device which can be controlled to have an output voltage rising and falling fast while a driving frequency is controlled without exceeding a resonance frequency. <P>SOLUTION: The power supply device has a piezoelectric transformer 101 which generates voltage output, rectifying elements (102, 103, and 104) which rectify, smooth, and output the voltage output from the piezoelectric transformer 101 to a load, a comparing element (109) which compares the output voltage output by the rectifying element with an input control voltage (Vcont), a voltage-controlled oscillator (VCO) 110 capable of controlling the driving frequency to be output according to the output voltage output by the comparing element, and piezoelectric transformer driving elements (111, 112) which drive the piezoelectric transformer according to the driving frequency controlled by the voltage-controlled oscillator, and is equipped with frequency modulating elements (124, 137) for modulating the driving frequency of the voltage-controlled oscillator (VCO) 110 according to an input frequency modulation signal (Fcont). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power supply apparatus suitable for an image forming apparatus for forming an image by an electrophotographic process, and more particularly to a power supply apparatus using a piezoelectric transformer and an image forming apparatus including the power supply apparatus.

  In a conventionally known electrophotographic image forming apparatus, when a direct transfer method in which a transfer member is brought into contact with a photosensitive member is employed, the transfer member has a roller-like conductivity having a conductor shaft. Using rubber, it is driven to rotate according to the process speed of the photoreceptor.

  A DC bias voltage is used as the voltage applied to the transfer member. At this time, the polarity of the DC bias voltage is the same as that of a normal corona discharge transfer voltage. However, in order to perform good transfer using such a transfer roller, it is usually necessary to apply a voltage of 3 kV or more (required current is several μA) to the transfer roller. In order to generate a high voltage required for the image forming process as described above, a winding type electromagnetic transformer has been conventionally used. However, the electromagnetic transformer is composed of a copper wire, bobbin, and magnetic core. When used in an image forming apparatus having the above specifications, the output current value is a small current of several μA. The leakage current had to be reduced to the maximum. Therefore, it is necessary to mold the winding of the transformer with an insulator, and a large transformer is required as compared with the supplied power, which hinders miniaturization and weight reduction of the high-voltage power supply device.

  Therefore, in order to compensate for these drawbacks, it has been studied to generate a high voltage by using a thin and light high-power piezoelectric transformer. That is, by using a piezoelectric transformer made of ceramic, it is possible to generate a high voltage with an efficiency higher than that of an electromagnetic transformer, and the primary side and the secondary side regardless of the coupling between the primary side and the secondary side. Since it is possible to increase the distance between the electrodes, there is no need to mold for special insulation, so that an excellent characteristic that the high-pressure generator can be made smaller and lighter is obtained.

  Here, a conventional example of a piezoelectric transformer type high voltage power supply will be described with reference to FIG. The circuit shown in FIG. 13 is a high voltage power source, and 101 is a piezoelectric transformer (piezoelectric ceramic transformer) of the high voltage power source. The AC output of the piezoelectric transformer 101 is rectified and smoothed to a positive voltage by the diodes 102 and 103 and the high-voltage capacitor 104 and supplied to a transfer roller (not shown) as a load. The output voltage is divided by the resistors 105, 106, and 107, and input to the non-inverting input terminal (+ terminal) of the operational amplifier 109 that is a comparison circuit via the protective resistor 108. On the other hand, a high-voltage power supply control signal (Vcont), which is an analog signal, is input from the DC controller 201 to the connection terminal 118 via the resistor 114 to the inverting input terminal (−terminal) of the operational amplifier 109.

  By connecting the operational amplifier 109, the resistor 114, and the capacitor 113 as shown in FIG. 13 to form an integrating circuit, a control signal (Vcont) smoothed with an integration time constant determined by the component constants of the resistor 114 and the capacitor 113 is obtained. 109 is input. The output terminal of the operational amplifier 109 is connected to a voltage controlled oscillator (VCO) 110 (piezoelectric transformer driving frequency generating means), and the output terminal of the voltage controlled oscillator (VCO) 110 is connected to the base of the transistor 111. The collector of the transistor 111 is connected to the power supply (+24 V) via the inductor 112 and at the same time connected to one of the electrodes on the primary side of the piezoelectric transformer 101. The other of the primary side electrodes is grounded. The emitter of the transistor 111 is also grounded. Note that the voltage controlled oscillator (VCO) 110 operates such that the output frequency (output piezoelectric transformer driving frequency) decreases when the input voltage increases, and the output frequency increases when the input voltage decreases.

  In general, the characteristics of the piezoelectric transformer have such a wide shape that the output voltage becomes maximum at the resonance frequency f0 as shown in FIG. 4, and the output voltage can be controlled by the frequency. When the output voltage of the piezoelectric transformer is increased, the drive frequency is increased from a lower frequency (for example, F1 shown in FIG. 4) to a higher one (for example, shown in FIG. 4) in a frequency region lower than the resonance frequency f0 of the piezoelectric transformer. It becomes possible by changing to F2).

  With this configuration of the conventional example, when the output voltage of the piezoelectric transformer 101 increases, the input voltage of the non-inverting input terminal (+ terminal) of the operational amplifier 109 also increases via the resistor 105, and the voltage of the output terminal of the operational amplifier 109 increases. Then, since the input voltage of the voltage controlled oscillator (VCO) 110 increases, the driving frequency of the piezoelectric transformer 101 decreases. As the drive frequency decreases, the output voltage of the piezoelectric transformer 101 decreases, and as a result, control is performed in the direction of decreasing the output voltage. That is, this circuit constitutes a negative feedback control circuit.

  On the other hand, when the output voltage of the piezoelectric transformer 101 decreases, the input voltage at the non-inverting input terminal (+ terminal) of the operational amplifier 109 also decreases, and the voltage at the output terminal of the operational amplifier 109 decreases. That is, since the input voltage of the voltage controlled oscillator (VCO) 110 decreases, the drive frequency of the piezoelectric transformer 101 increases, and as a result, the piezoelectric transformer 101 is controlled in the direction of increasing the output voltage. Thus, the voltage is determined by the voltage of the control signal (Vcont) from the DC controller 201 input to the inverting input terminal (− terminal) of the operational amplifier 109 (control voltage: hereinafter, this control voltage is also expressed as Vcont). The output voltage is constant voltage controlled so as to be equal.

As the above-described prior art, for example, there is one disclosed in Patent Document 1 below.
JP-A-11-206113

However, in the case of the above conventional example, when the integration time constant of the integration circuit composed of the operational amplifier 109, the resistor 114, and the capacitor 113 is increased, the operational amplifier 109 inputs the voltage controlled oscillator (VCO) 110 when the output voltage rises. When an overshoot occurs in the control signal, resulting in an output voltage overshoot, and when the control voltage is in the vicinity of the resonance frequency f0, the drive frequency of the piezoelectric transformer 101 exceeds the resonance frequency f0 and f0. As a result, the output voltage may not be controlled.
On the other hand, if the integration time constant is delayed so that it does not exceed f0 beyond the resonance frequency f0, the control signal to the voltage controlled oscillator (VCO) 110 is also delayed, the occurrence of output voltage overshoot is eliminated, and the piezoelectric transformer 101 Control without worrying that the drive frequency exceeds the resonance frequency f0 is possible.

  However, since the rise of the output voltage is delayed as a result, it is necessary to raise the control voltage (Vcont) early in order to apply a constant high voltage to the transfer member at a predetermined timing. There was a possibility of image failure due to the application of high pressure.

  The present invention has been made in view of the above problems. In a power supply device using a piezoelectric transformer, it is possible to quickly control the rise and fall of an output voltage, and to prevent the resonance frequency (f0) from being exceeded. It is an object of the present invention to provide a power supply device capable of controlling a driving frequency and the power supply device.

  In order to achieve the above object, a power supply apparatus according to the present invention is mainly characterized by having the following configuration.

That is, according to the present invention, a piezoelectric transformer that outputs a voltage, a rectifier that rectifies and smoothes a voltage output from the piezoelectric transformer, and an output voltage that is output by the rectifier. A comparison element for comparing the control voltage, a voltage controlled oscillator capable of controlling a drive frequency to be output according to an output voltage output from the comparison element, and a drive frequency controlled by the voltage controlled oscillator. Based on this, a power supply device having a piezoelectric transformer driving element for driving the piezoelectric transformer,
A frequency modulation element for modulating the drive frequency of the voltage controlled oscillator based on the input frequency modulation signal is provided.

  Preferably, in the power supply device described above, the frequency modulation element modulates the driving frequency of the voltage controlled oscillator by alternately hopping two frequencies according to an on / off period of the frequency modulation signal. And

  Preferably, in the power supply device described above, the frequency modulation element modulates a drive frequency of the voltage controlled oscillator by a modulation frequency that changes linearly.

  Preferably, in the power supply device described above, a modulation width variable element that varies a modulation width for modulating the drive frequency based on an output of the frequency modulation element and an output voltage output by the rectifying element is further provided. It is characterized by providing.

  According to the power supply device of the present invention, it is possible to quickly control the rise and fall of the output voltage while controlling the drive frequency so as not to exceed the resonance frequency.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a configuration diagram of an image forming apparatus (hereinafter referred to as “color laser printer”) including a high-voltage power supply device 202 using a piezoelectric transformer. The color laser printer 401 has a deck 402 for storing the recording paper 32, a deck paper presence sensor 403 for detecting the presence or absence of the recording paper 32 in the deck 402, a pickup roller 404 for feeding the recording paper 32 from the deck 402, and a pickup roller 404. Are provided with a deck feed roller 405 for transporting the recording paper 32 fed out by the above and a deck feed roller 405, and a retard roller 406 for preventing double feeding of the recording paper 32 is provided.

  A registration roller pair 407 that synchronously conveys the recording paper 32 and a pre-registration sensor 408 that detects the conveyance state of the recording paper 32 to the registration roller pair 407 are disposed on the downstream side of the deck paper feeding roller 405. Further, an electrostatic attraction conveyance transfer belt (hereinafter referred to as “ETB”) 409 is disposed downstream of the registration roller pair 407, and four colors (yellow (Y), magenta (M) described later are disposed on the ETB 409. ), Cyan (C), black (K)) of process cartridges 410Y, 410M, 410C, 410K, and an image formed by an image forming unit including the scanner units 420Y, 420M, 420C, 420K, transfer rollers 430Y, 430M. A color image is formed by being sequentially superposed by 430C and 430K, and is transferred and conveyed onto the recording paper 32.

  Further, on the downstream side, in order to thermally fix the toner image transferred onto the recording paper 32, a pair of a fixing roller 433 and a pressure roller 434 each having a heating heater 432 inside, and the recording paper 32 from the fixing roller is conveyed. For this purpose, a pair of fixing paper discharge rollers 435 and a fixing paper discharge sensor 436 for detecting the conveyance state from the fixing unit are provided.

  Each scanner unit 420 emits a laser beam modulated based on each image signal sent from a video controller 440 described later, and the laser beam from each laser unit 421 is placed on each photosensitive drum 305. It comprises a polygon mirror 422 for scanning, a scanner motor 423, and an imaging lens group 424.

Each process cartridge 410 includes a photosensitive drum 305, a charging roller 303, a developing roller 302, and a toner storage container 411 necessary for a known electrophotographic process, and is configured to be detachable from the color laser printer 401. .
Further, upon receiving image data sent from an external device 441 such as a personal computer (host computer), the video controller 440 develops the image data into bitmap data and generates an image signal for image formation.

  Reference numeral 201 denotes a DC controller which is a control unit of the laser printer. The RAM 207a, ROM 207b, timer 207c, digital input / output port 207d, MPU (microcomputer) 207 provided with a D / A port 207e, and various input / output control circuits (Not shown).

  Reference numeral 202 denotes a high-voltage power supply (high-voltage power supply, hereinafter simply referred to as “power supply”), a charging high-voltage power supply (not shown) corresponding to each process cartridge (410Y, 410M, 410C, and 410K), a development high-voltage power supply ( (Not shown) and a transfer high-voltage power source using a piezoelectric transformer capable of outputting a high voltage corresponding to each transfer roller 430. As a configuration of the power supply device 202, any one of the configurations of the first to third embodiments described below is provided.

  Next, the configuration of a transfer high-voltage power source using a piezoelectric transformer will be described with reference to FIG. Note that the configuration of a transfer high-voltage power supply (hereinafter also simply referred to as “transfer high-voltage power supply”) using the piezoelectric transformer according to the present embodiment is effective for both positive voltage and negative voltage output circuits. Here, a transfer high-voltage power supply that typically requires a positive voltage will be described.

  The transfer high-voltage power supply is provided with four circuits corresponding to the transfer rollers 430Y, 430M, 430C, and 430K of yellow (Y), magenta (M), cyan (C), and black (K). Since the configuration is the same for each circuit, only one circuit will be described in FIG. 1. However, the gist of the present invention is not limited to one circuit, and it can be applied to a configuration in which four or more transfer high-voltage power supplies are provided. Needless to say.

  FIG. 1 is a diagram showing a configuration of a piezoelectric transformer type high-voltage power supply according to a first embodiment of the present invention. In FIG. 1, reference numeral 110 denotes a voltage controlled oscillator (VCO). The VCO 110 of this embodiment includes a comparator 121 as a comparison element, a charge / discharge operation capacitor 120 connected to an inverting input terminal (− terminal) of the comparator 121, a resistance element 126, and a non-inverting input terminal (+ terminal) of the comparator 121. A CR oscillation circuit comprising resistance elements 122 and 123 for generating charge threshold voltage and discharge threshold voltage, and a diode 127, which are connected to each other, is connected as a basic configuration. An emitter follower circuit including a transistor 128 and resistance elements 129, 130, and 131 is connected in parallel with the resistance element 126, and the charging current to the capacitor 120 is made variable, so that the driving frequency is determined according to the output voltage from the operational amplifier 109. Can be controlled.

  In FIG. 1, the transistor 125 and the resistor 132 increase the rise time of the output terminal of the comparator 121, and the resistor 133 is a base resistance for the transistor 111. Further, the diode 134 is a protection diode for the transistor 128. The capacitor 140 is for removing noise superimposed on the output detection voltage. Since the details of the above components are out of the gist of the present embodiment of the invention, detailed description thereof is omitted.

  The resistor 124 and the transistor 137 function as a frequency modulation element for modulating the output frequency (driving frequency) output from the voltage controlled oscillator (VCO) 110 based on the input frequency modulation signal (Fcont).

  The power supply device according to the first embodiment of the present invention includes a piezoelectric transformer 101 that outputs a voltage, and a rectifier element (102, 103, 104) that rectifies and smoothes the voltage output from the piezoelectric transformer 101 with respect to a load. And a comparison element (109) that compares the output voltage output from the rectifying element and the input control voltage (Vcont), and the drive frequency to be output can be controlled according to the output voltage output from the comparison element Power supply device having a voltage controlled oscillator (VCO) 110 and a piezoelectric transformer driving element (111, 112) for driving a piezoelectric transformer based on a driving frequency controlled by the voltage controlled oscillator, the frequency being input A frequency modulation element (124) for modulating the drive frequency of the voltage controlled oscillator (VCO) 110 based on the modulation signal (Fcont). Characterized in that it comprises 137).

  The frequency modulation elements (124, 137) modulate the driving frequency of the voltage controlled oscillator by alternately hopping two frequencies according to the on / off period of the frequency modulation signal (Fcont).

  Next, frequency modulation will be specifically described. First, when the transistor 137 is off, the charging threshold voltage (Vsc (off)) related to the drive frequency of the voltage controlled oscillator (VCO) 110 is expressed by the equation (1) obtained by dividing the 24V power supply by the resistance elements 122 and 123.

Vsc (off) = 24V × R123 ÷ (R122 + R123) (1)
Further, when the transistor 137 is on, the charging threshold voltage (Vsc (on)) is expressed by the equation (2) obtained by dividing the 24V power source by the resistance elements 122 and 123 and the resistance element 124.

Vsc (on) = 24V × (R123 × R124) ÷ (R122 × R123 + R123 × R124 + R124 × R122)
... (2)
Since Vsc (on) is lower than Vsc (off), the drive frequency (VCO frequency) of the voltage controlled oscillator (VCO) 110 when the transistor 137 is on is always higher than when the transistor 137 is off. The voltage controlled oscillator (VCO) 110 is switched between two frequencies by repeatedly turning on and off the transistor 137 at predetermined intervals via resistors 135 and 136 by a frequency modulation signal (Fcont) from a DC controller 201 (not shown in FIG. 1). Are alternately hopped and frequency modulated.

  In other words, the voltage controlled oscillator (VCO) 110 alternately outputs two frequencies that change based on the control signal from the operational amplifier 109.

  FIG. 3 is a diagram showing the operation of each part during frequency modulation in the piezoelectric transformer type high-voltage power supply according to the first embodiment. In FIG. 3A, a waveform a is a frequency modulation signal (Fcont) and is shown as a waveform that outputs a pulse having a period T (s). In synchronization with this frequency modulation signal (Fcont), the charging threshold voltage changes between Vsc (on) and Vsc (off), as seen in the inverting input terminal waveform of the comparator 121 (waveform b in FIG. 3B). The voltage at which the capacitor 120 is switched from charging to discharging also changes. As a result, the drive frequency (VCO frequency) of the voltage controlled oscillator (VCO) 110 is modulated while alternately hopping (frequency hopping) between F1 and F2 (F1 <F2) (waveform c: frequency in FIG. 3C). The VCO frequency is modulated in synchronization with the modulation signal (thick solid line).

  When the drive frequencies F1 and F2 are both equal to or lower than the resonance frequency fo of the piezoelectric transformer 101, the output peak voltage of the piezoelectric transformer 101 is the output voltage (Vh2) at the time of driving at the drive frequency F2, as shown in FIG. It becomes higher than the driving output voltage (Vh1) at the driving frequency F1.

  Here, the pulse period T (s) of the frequency modulation signal (Fcont) is determined from the discharge time constant (RL) obtained from the load resistance (RL) of the high-voltage power source by the capacitor 104 of the rectifier circuit, the output voltage detection resistor element 105, the transfer roller, and the like. By making it sufficiently shorter than τ = C104 × (R105 × RL) ÷ (R105 + RL)) and longer than the cycle time of the lowest usable drive frequency of the piezoelectric transformer 101, the output voltage after rectification is alternated by frequency modulation. The higher output peak voltage of the output piezoelectric transformer 101 (Vh2 in the waveform (d) in FIG. 3) is peak-held.

In this embodiment,
C104 discharge time constant (τ): several hundred mS (3)
Minimum driving frequency of piezoelectric transformer: several μS to several tens μS (4)
Therefore, the frequency modulation pulse period T is between several tens of μS to several hundreds of μS, and good results are obtained in which the ripple of the output voltage is also suppressed.

  With the above configuration, the apparent frequency characteristic of the piezoelectric transformer 101 shifts a predetermined frequency (ft) in the frequency axis direction as shown in FIG. 5, and any high voltage (Vht) (in the drawing) (Part indicated by a solid line) is output. FIG. 5 shows F2 on the horizontal axis as the drive frequency. In FIG. 5, ft indicates the shifted frequency. In this case, the output voltage of the piezoelectric transformer 101 is higher than the output voltage Vh0 before the shift, and Vht is output as the output voltage.

  Next, characteristics of the control voltage, drive frequency (VCO frequency), and output voltage when the high voltage output voltage is raised will be described with reference to FIGS. FIG. 6 shows a case where the output voltage normally rises to the target voltage (Vht) (FIG. 6C), the control voltage (Vcont) (FIG. 6A), and the drive frequency of the voltage controlled oscillator (VCO) 110 ( It is a figure which shows the waveform of (VCO frequency) (FIG.6 (b)). As the output control voltage shown in FIG. 6A rises, the output voltage of the operational amplifier 109 decreases, the drive frequencies F1 and F2 output alternately from the voltage controlled oscillator (VCO) 110 increase, and output alternately from the piezoelectric transformer 101. The output peak voltages (Vh1, Vh2) to be increased are also increased. Since the output voltage after rectification peaks and holds the higher of Vh1 and Vh2, in FIG. 6, the peak voltage of Vh2 is equal to Vht.

  On the other hand, FIG. 7 shows an abnormal load fluctuation of the high voltage output due to foreign matter mixed between the transfer roller 430 and the photosensitive drum 105 at the time of starting the high voltage output, instantaneous output voltage erroneous detection due to impulse external noise, etc. Waveform (FIG. 7 (c)), control voltage (Vcont) (FIG. 7 (a)), drive frequency (VCO frequency) of the voltage controlled oscillator (VCO) (FIG. 7) It is a figure which shows the waveform of (b). In this case, as in FIG. 7, the output voltage of the operational amplifier 109 decreases with the rise of the output control voltage due to the control voltage (Vcont), and the drive frequencies F1 and F2 output alternately from the voltage controlled oscillator (VCO) 110 increase. The output peak voltages (Vh1, Vh2) output alternately from the piezoelectric transformer 101 also increase.

  When an overshoot occurs in the output voltage of the voltage controlled oscillator (VCO) 110 due to the above-described causes, the drive frequency F2 exceeds the resonance frequency fo, the frequency further increases, and the voltage of Vh2 starts to decrease. By making the apparent frequency characteristic shown in FIG. 5 so that the voltage of Vh1 does not exceed the target voltage (Vht) at this time, the output of Vh1 increases as the frequency increases, and the output voltage becomes the target voltage (Vht). Controlled.

  In the present embodiment, a comparative integration circuit composed of an operational amplifier 109 and the like, a voltage controlled oscillator (VCO) 110, a piezoelectric transformer driving element composed of a transistor 111 and the like, and a frequency modulation element composed of a transistor 137 and the like are discrete components. Although it is configured, an IC may be formed on the same chip. In this case, the power supply device can be made smaller and lighter.

  According to the power supply device according to the present embodiment, it is possible to quickly control the rising and falling of the output voltage while controlling the drive frequency so as not to exceed the resonance frequency.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to the drawings. FIG. 8 is a diagram showing a configuration of a piezoelectric transformer type high-voltage power supply according to the second embodiment of the present invention. The difference from FIG. 1 according to the first embodiment is that the resistance element 124 of the frequency modulation circuit is directly connected to the frequency modulation signal (Fcont) from the DC controller 201 (not shown in FIG. 8). is there.

  With the configuration shown in FIG. 8, by outputting a frequency modulation signal (Fcont) from the D / A port of the DC controller 201, the charging threshold voltage can be varied in an analog manner, and as a result, the modulation frequency is changed linearly. It becomes possible.

  The frequency modulation element (124) modulates the drive frequency of the voltage controlled oscillator by a linearly changing modulation frequency.

  FIG. 9 is a diagram showing the operation of each part during frequency modulation in the second embodiment. A waveform a2 in FIG. 9A is a frequency modulation signal (Fcont), and the waveform a2 shows a waveform that linearly changes between Vfc (L) and Vfc (H) in a cycle 2T (s). . The charging threshold voltage linearly changes between Vsc (L) and Vsc (H) in synchronization with the frequency modulation signal (Fcont), and the inverted input terminal waveform of the comparator 121 (waveform b in FIG. 9B). The voltage at which the capacitor 120 is switched from charging to discharging as shown in FIG. Thus, the drive frequency (VCO frequency) of the voltage controlled oscillator (VCO) 110 is modulated while changing between F1 (L) and F2 (H) (F1 (L) <F2 (H)) (FIG. Waveform c) of 9 (c). When both F1 (L) and F2 (H) are less than or equal to the resonance frequency of the piezoelectric transformer 101, the output voltage of the piezoelectric transformer 101 is on the F2 (H) side where the drive frequency is high, as in the first embodiment. (Vh2 (H)) is higher than that on the F1 (L) side (Vh1 (H)) (waveform d in FIG. 9D).

  With the above configuration, the apparent frequency characteristic of the piezoelectric transformer 101 is a characteristic that outputs the highest voltage generated between the frequencies F1 (L) and F2 (H) that are frequency-modulated, as shown in FIG. It becomes. That is, until the frequency of F2 (H) exceeds the resonance frequency f0, a voltage obtained by driving the piezoelectric transformer 101 at the frequency F2 (H) is output, the frequency of F2 (H) exceeds f0, and F1 (L Until the frequency of) exceeds f0, the output voltage when the piezoelectric transformer 101 is driven at f0 is maintained. FIG. 10 shows the frequency of F2 (H) on the horizontal axis. By making the apparent frequency characteristics of the piezoelectric transformer 101 as shown in FIG. 10, an overshoot occurs in the output voltage of the voltage controlled oscillator (VCO) 110 for the same reason as in the first embodiment, and F2 (H) Since the output voltage can maintain the maximum output (Vhtmax) until the frequency of F1 (L) exceeds the resonance frequency f0 even when the frequency of the high frequency power supply circuit exceeds the resonance frequency fo, the high voltage power supply circuit In the case of FIG. 10, the output voltage can be controlled to the target voltage in the frequency region on the left side of the drawing with respect to the resonance frequency f0.

  According to the power supply device according to the present embodiment, it is possible to quickly control the rising and falling of the output voltage while controlling the drive frequency so as not to exceed the resonance frequency.

[Third Embodiment]
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. FIG. 11 is a diagram showing a configuration of a piezoelectric transformer type high-voltage power supply according to the third embodiment of the present invention. The difference from FIG. 1 according to the first embodiment is that the output voltage detection signal input to the non-inverting input terminal (+ terminal) of the operational amplifier 109 is separately provided from a voltage follower circuit configured by the operational amplifier 200. In this way, the resistor 124 of the frequency modulation circuit and the collector of the transistor 137 are connected.

  The resistor 201 is an output protection resistor of the operational amplifier 200.

  A modulation width variable element (201) that varies the modulation width for modulating the drive frequency based on the output of the frequency modulation element and the output voltage (Vout) output from the rectifying element is further provided.

  With the configuration shown in FIG. 11, as described in the first embodiment, frequency hopping between the modulation frequencies (F1, F2) is performed, and the charging threshold voltage is changed according to the output voltage of the high-voltage power source. The modulation width of the frequency modulation can be changed according to the output voltage of the power supply.

  Here, the relationship between the output voltage detection signal (Vsns) and the output voltage is expressed by the following equation (5).

  First, the output voltage detection signal outputs a value of the following expression according to the output voltage (Vout).

Vsns = α + β · Vout (5)
Here, α and β are expressed by equations (6) and (7).

α = R107 x R105 ÷ (R106 x R107 + R107 x R105 + R105 x R106) x Vref ... (6)
β = R106 x R107 ÷ (R106 x R107 + R107 x R105 + R105 x R106) ... (7)
At this time, the charging threshold voltage Vsc2 (off) when the transistor 137 is turned off is obtained as equation (8).

Vsc2 (off) = γ + δ · Vsns
= Γ + δ · α + δ · β · Vout (8)
Here, γ and δ are expressed by equations (9) and (10), respectively.

γ = R123 x R124 ÷ (R122 x R123 + R123 x R124 + R124 x R122) x 24V ... (9)
δ = R122 × R123 ÷ (R122 × R123 + R123 × R124 + R124 × R122) ... (10)
Similarly, the charging threshold voltage Vsc2 (ON) when the transistor 137 is on can be obtained as equation (11).

Vsc2 (ON) = γ + δ · α (11)
The charging threshold voltage changes by ΔVsc expressed by equation (12) when the transistor 137 is turned on / off.

ΔVsc = δ · β · Vout (12)
Since the frequency modulation width increases as the change amount (ΔVsc) of the charging threshold voltage increases, the frequency modulation width can be increased as the output voltage (Vout) of the high-voltage power supply increases. With the configuration shown in FIG. 11, the apparent frequency characteristic of the piezoelectric transformer 101 is shifted by a predetermined frequency (ft1) in the frequency axis direction as shown in FIG. 12, and any high voltage (Vht1) (see FIG. The portion indicated by the solid line in the figure) is output. It is possible to suppress fluctuations in the output voltage of the piezoelectric transformer 101 due to frequency modulation when the output voltage is low (when Vht2 (drive frequency ft2) or less) (in FIG. 12, the broken line portion and the solid line portion overlap).

  According to the power supply device of the present embodiment, by frequency hopping between the modulation frequencies, making the modulation frequency width variable according to the output voltage, and further increasing the modulation frequency width as the absolute value of the output voltage increases. The integration time constant of the control voltage (Vcont) determined by the resistor 114 and the capacitor 113 is increased, and the output voltage can be quickly controlled to rise and fall.

  According to the power supply device according to the present embodiment, it is possible to quickly control the rising and falling of the output voltage while controlling the drive frequency so as not to exceed the resonance frequency.

It is a figure which shows the structure of the piezoelectric transformer type high voltage power supply concerning 1st Embodiment of this invention. 1 is a configuration diagram of an image forming apparatus including a power supply device using a piezoelectric transformer. It is the figure which showed operation | movement of each part at the time of the frequency modulation in the power supply device concerning 1st Embodiment. It is a figure which shows the frequency characteristic of the piezoelectric transformer concerning 1st Embodiment. It is a figure which shows the apparent frequency characteristic of the piezoelectric transformer at the time of the frequency modulation of 1st Embodiment. It is a figure which shows the characteristic of the control voltage at the time of the high voltage | pressure start-up at the time of normal time concerning 1st Embodiment, a drive frequency (VCO frequency), and an output voltage. It is a figure which shows the characteristic of the control voltage at the time of the high voltage | pressure start time at the time of the overshoot generation concerning 1st Embodiment, a drive frequency (VCO frequency), and an output voltage. It is a figure which shows the structure of the piezoelectric transformer type high voltage power supply concerning 2nd Embodiment. It is the figure which showed each part operation | movement at the time of the frequency modulation in the power supply device concerning 2nd Embodiment. It is a figure which shows the apparent frequency characteristic of the piezoelectric transformer at the time of the frequency modulation of 2nd Embodiment. It is a figure which shows the structure of the piezoelectric transformer type high voltage power supply concerning 3rd Embodiment of this invention. It is a figure which shows the apparent frequency characteristic of the piezoelectric transformer at the time of the frequency modulation of 3rd Embodiment. It is a figure which shows the prior art example of a piezoelectric transformer type high voltage power supply.

Claims (8)

The piezoelectric transformer that performs voltage output, the rectifier that outputs the voltage output from the piezoelectric transformer by rectifying and smoothing the load, and the output voltage output by the rectifier and the input control voltage are compared. The comparison element, a voltage controlled oscillator capable of controlling the drive frequency to be output according to the output voltage output from the comparison element, and driving the piezoelectric transformer based on the drive frequency controlled by the voltage controlled oscillator A power supply device having a piezoelectric transformer driving element to
A power supply apparatus comprising: a frequency modulation element for modulating a drive frequency of the voltage controlled oscillator based on an input frequency modulation signal. 2. The power supply according to claim 1, wherein the frequency modulation element modulates the driving frequency of the voltage controlled oscillator by alternately hopping two frequencies according to an ON / OFF period of the frequency modulation signal. apparatus. The power supply device according to claim 1, wherein the frequency modulation element modulates a driving frequency of the voltage controlled oscillator by a linearly changing modulation frequency. 2. A modulation width variable element that varies a modulation width for modulating the drive frequency based on an output of the frequency modulation element and an output voltage output by the rectifying element. 4. The power supply device according to any one of items 1 to 3. The power supply device according to claim 4, wherein the modulation width variable element widens the modulation width as an absolute value of the output voltage increases. 2. The same IC chip is provided with the comparison element, the voltage controlled oscillator, the piezoelectric transformer driving element, the frequency modulation element, and the modulation width variable element. The power supply apparatus in any one of thru | or 5. The power supply device according to any one of claims 1 to 6,
An image forming apparatus comprising: an image forming unit configured to form an image with a voltage output generated by the power supply device. The image forming apparatus according to claim 7, wherein the image forming unit forms an image by an electrophotographic process.

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