JP2009171832A - High-tension power supply, image forming device having the same, and circuit board of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To save time in a manually soldering process, reduce a mounting cost, and further eliminate a mounting error due to the manual processing in a piezotransducer-type high tension power supply. <P>SOLUTION: The high-tension power supply having a circuit board including the piezotransducer, a frequency control transmitter that generates a frequency signal to operate the piezotransducer in response to a control signal, a switching element that is connected to a primary side of the piezotransducer and performs switching operations in response to the frequency signal, a capacitor and an inductor composing a parallel resonant circuit that performs resonant operations with the switching element and switching operations, and a capacitive element that is connected between the power supply side of the inductor and a gland, wherein the capacitive element and inductor are disposed on the circuit substrate so as to be dipped in a solder flow tank prior to the dipping of the piezotransducer is provided. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a high voltage output circuit using a piezoelectric transformer, a high voltage power supply apparatus having the high voltage output circuit, an image forming apparatus having the high voltage power supply apparatus, and a circuit board thereof.

  In recent color laser printers or the like, an image of each color is formed by independently scanning light beams from a plurality of optical devices on a plurality of photoconductors provided corresponding to the respective colors. These color images are superimposed on the intermediate transfer belt and then transferred onto the recording paper. Such a method is called a tandem method, in which a plurality of color toner images are formed in parallel, and these are superimposed on an intermediate transfer belt and transferred onto a recording sheet, so that a final color image is formed. Time can be significantly reduced.

  In the electrophotographic process employed in such a color laser printer, for example, a DC voltage is used as a charging bias applied to the charging roller, a developing bias applied to the developing device, and a transfer bias applied to the transfer roller. ing. Each of these biases requires a high voltage. For example, in order to perform good transfer in the transfer bias, a DC voltage of 3 kV or more is usually required.

  Conventionally, a wound electromagnetic transformer has been used to generate a high voltage in a laser printer. However, this electromagnetic transformer is composed of a copper wire, a bobbin, and a magnetic core. When a voltage of 3 kV or more is applied as described above, an output current value is a small current of several μA, and thus a leakage current. Had to be minimized. Therefore, it is necessary to mold the winding of the transformer with an insulating material, and a large transformer is required as compared with the supplied power. For this reason, it has been an obstacle to miniaturization and weight reduction of the high-voltage power supply device.

  Therefore, in order to realize a reduction in size and weight of a high-voltage power supply device, a high-voltage generator that generates a high voltage using a thin and lightweight high-output piezoelectric transformer (piezoelectric ceramic transformer) has begun to be adopted. By using such a piezoelectric element made of ceramic as a piezoelectric transformer, a high voltage can be generated with efficiency higher than that of an electromagnetic transformer. In addition, since the distance between the primary and secondary electrodes can be increased regardless of the coupling between the primary side and the secondary side, it is not necessary to perform a special molding process for insulation. Thereby, there is an advantage that the high voltage generator can be made small and light, and it can contribute to the miniaturization of the device as compared with the case where the winding type electromagnetic transformer is used. As a high-voltage power supply device using such a piezoelectric transformer, for example, there is one described in Patent Document 1.

  FIG. 12 is a block diagram showing an example of a conventional high-voltage power supply device using a piezoelectric transformer. FIG. 12 shows an example of a circuit that outputs a negative bias (negative high voltage) as an example.

  In the figure, reference numeral 101 denotes a piezoelectric transformer of a high voltage power source. The output of the piezoelectric transformer 101 is rectified and smoothed to a negative voltage by the diodes 102 and 103 and the high voltage capacitor 104, and supplied from an output end 116 to a charging 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 through the protective resistor 108. On the other hand, a control signal Vcont of a high voltage power source, which is an analog signal, is input via a connection terminal 118 from a control unit (not shown) of a printer housing the high voltage power source device. This control signal is input to the inverting input terminal (− terminal) of the operational amplifier 109 via the resistor 114. Here, the operational amplifier 109, the resistor 114, and the capacitor 113 constitute an integrating circuit.

  The output of the operational amplifier 109 is connected to a voltage controlled oscillator (VCO) 110, and the output of the voltage controlled oscillator 110 is connected to an FET 111 connected to an LC parallel resonant circuit formed by an inductor 112 and a capacitor 115. The frequency of the signal output from the voltage controlled oscillator 110 increases as the input voltage of the voltage controlled oscillator 110 increases, and decreases as the input voltage decreases. Therefore, the voltage controlled oscillator 110 outputs a signal having a frequency corresponding to the level of the input voltage. The output signal of the voltage controlled oscillator 110 drives the above-described LC resonance circuit, so that a voltage corresponding to the control signal (Vcont) is finally supplied to the primary side of the piezoelectric transformer 101.

  FIG. 13 is a diagram showing the characteristics of the output voltage with respect to the drive frequency of the piezoelectric transformer 101.

As shown in the figure, the piezoelectric transformer 101 has a characteristic that the output voltage becomes maximum at the resonance frequency f0, and it can be seen that the output voltage can be controlled by the frequency. Here, for example, the drive frequency when the specified output voltage Edc is output is fx. As described above, the output frequency of the voltage controlled oscillator 110 changes according to the control signal Vcont. Therefore, when the piezoelectric transformer 101 is controlled to obtain an output voltage higher than the output voltage Edc, the output frequency of the voltage controlled oscillator 110 is set to a frequency lower than fx. When the control is performed so as to obtain a voltage lower than the output voltage Edc, the output frequency of the voltage controlled oscillator 110 is set to a frequency higher than fx. That is, in the circuit shown in FIG. 12, the output voltage of the output terminal 116 is controlled at a constant voltage so as to be equal to the voltage determined by the voltage of the control signal Vcont input to the inverting input terminal (−terminal) of the operational amplifier 109. A negative feedback control circuit.
JP-A-11-206113

  However, the conventional piezoelectric transformer type high voltage power supply device has the following problems.

  When various components are automatically mounted on the circuit board of the piezoelectric transformer type high voltage power supply device, an excessive voltage is generated between the terminals due to the pyroelectric effect of the piezoelectric transformer due to the heat of the solder flow tank (solder tank). Due to this excessive voltage, the voltage applied to the FET 111 for driving the piezoelectric transformer connected via the wiring on the substrate exceeds the withstand voltage, and the FET 111 is destroyed. there were.

  To solve this problem, conventional piezoelectric transformer type high-voltage power supply devices automatically mount parts other than the piezoelectric transformer using a solder flow tank when mounting the board, and then manually solder the piezoelectric transformer to the board. Had gone. However, for example, a large number of piezoelectric transformers are mounted on a circuit board of a high-voltage power supply device used in a tandem color laser printer, and a lot of time is required for a manual soldering process, resulting in an increase in mounting cost. Further, since it is a soldering operation by human hands, there is a possibility that a mounting error may occur, and there is a limit in terms of improvement in yield and productivity.

  The present invention has been made for the purpose of solving the above-mentioned problems.

  The present invention is characterized by a high voltage output circuit that enables automatic mounting of a piezoelectric transformer on a substrate, a high voltage power supply device having the high voltage output circuit, and an image forming apparatus using the high voltage power supply device. The purpose is to provide.

In order to achieve the above object, a high-voltage power supply device according to one embodiment of the present invention has the following configuration. That is,
Piezoelectric transformer, frequency-controlled oscillator that generates a frequency signal for driving the piezoelectric transformer, a switching element that is connected to a primary side of the piezoelectric transformer and performs a switching operation according to the frequency signal, and a switching operation by the switching element A high-voltage power supply device having a circuit board having a capacitor and an inductor constituting a parallel resonant circuit that performs a resonant operation by:
The circuit board has a capacitive element connected between the power supply side of the inductor and the ground,
When the circuit board is soldered by the solder flow method, the capacitive element, the inductor, and the piezoelectric transformer are arranged so that the piezoelectric transformer is mounted after the capacitive element and the inductor are mounted. It is characterized by.

In order to achieve the above object, a high-voltage power supply device according to one embodiment of the present invention has the following configuration. That is,
Piezoelectric transformer, frequency-controlled oscillator that generates a frequency signal for driving the piezoelectric transformer, a switching element that is connected to a primary side of the piezoelectric transformer and performs a switching operation according to the frequency signal, and a switching operation by the switching element A high-voltage power supply device having an inductor for performing resonance operation by
The circuit board has a capacitive element connected between the power supply side of the inductor and the ground,
When the circuit board is soldered by the solder flow method, the capacitive element, the inductor, and the piezoelectric transformer are arranged so that the piezoelectric transformer is mounted after the capacitive element and the inductor are mounted. It is characterized by.

  According to the present invention, there is an effect that it is possible to prevent the components forming the drive circuit of the piezoelectric transformer from being broken and to automatically mount the piezoelectric transformer.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. .

  FIG. 1 is a diagram illustrating a specific configuration example of a tandem color laser printer including a high voltage power supply device according to the present embodiment.

  Laser light from the laser scanner (11Y, 11M, 11C, 11K) is applied to the surface of the photoconductor (13Y, 13M, 13C, 13K) charged by the charging bias applied to the charging roller (15Y, 15M, 15C, 15K). Irradiate. Thereby, an electrostatic latent image of an image corresponding to each color is formed on each photoconductor. The electrostatic latent image is visualized by attaching toner of each corresponding color by a developing bias applied to the developing devices (16Y, 16M, 16C, 16K). Subsequently, the toner adhering to each photoconductor is sequentially superimposed and transferred onto the intermediate transfer belt 19 by the transfer bias applied to the transfer rollers (18Y, 18M, 18C, 18K) to form a color toner image. To do. In the drawing, Y is yellow, M is magenta, C is cyan, and K is black. The charging roller, laser scanner, and developing unit are for each color (Y, M, C, K). Is provided.

On the other hand, the recording paper 21 accommodated in the cassette 22 is fed by the paper feed roller 25 with its conveyance timing adjusted so that the toner image on the intermediate transfer belt 19 is transferred by the secondary transfer roller 29. . The recording paper 21 is conveyed by a registration roller 27, and a color toner image on the intermediate transfer belt 19 is transferred by a secondary transfer roller 29. Further, the recording paper 21 on which the color toner image is placed is fixed by the fixing device 30, and finally a color printed matter is obtained.
[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. However, the circuit diagrams shown in the embodiments described later are merely examples, and the present invention is not limited to these configurations.

  In the first embodiment, a capacitive element (capacitor) for reducing a voltage increase due to the pyroelectric effect of the piezoelectric transformer is connected between the power supply voltage Vcc and the ground. The capacitive element reduces the application of an excessive voltage generated by heating the piezoelectric transformer in the solder flow tank to the components of the drive circuit of the piezoelectric transformer. Thereby, destruction of the components used for the drive circuit of the piezoelectric transformer can be prevented. Moreover, it is not necessary to use a component having an excessive withstand voltage.

  FIG. 2 is a circuit diagram showing a configuration of a drive circuit of a piezoelectric transformer as a power supply circuit unit in the high voltage power supply device according to the first embodiment. Here, a high voltage power supply device that typically outputs a negative bias will be described as an example. The configuration of the high-voltage power supply device according to each embodiment described below is effective for both positive voltage and negative voltage outputs. As an example of the image forming apparatus provided with the high voltage power supply apparatus according to each of the following embodiments, a tandem color image forming apparatus shown in FIG.

  FIG. 2 shows a driving circuit for applying a voltage to a charging roller for charging a photoconductor on which a yellow (Y) image is formed and a charging roller for charging a photoconductor on which a magenta (M) image is formed. Is a circuit connected in parallel. In FIG. 2, Y and M are added to the end of the reference numerals of the respective drive circuits for yellow (Y) and magenta (Y). The configuration of the drive circuit is the same.

  In FIG. 2, each drive circuit is configured to be branched from a bypass capacitor 200 and wired. The bypass capacitor 200 provided at the branch point of the power supply is provided to prevent frequency interference when each drive circuit is driven at a different frequency. Therefore, the bypass capacitor 200 is preferably disposed in the vicinity of a power supply line from which power is branched to each drive circuit, and is generally disposed in the vicinity of a power supply connector (not shown).

  In the configuration of the drive circuit of the high voltage power supply device of the first embodiment shown in FIG. 2, the difference from the conventional example of FIG. 12 is that a capacitor 120Y is connected between the power supply side Vcc terminal of the inductor 112Y and the ground. In the point. Further, unlike the bypass capacitor 200 described above, the capacitor 120Y is arranged for each drive circuit as shown in the figure. The control of the piezoelectric transformer 101 is the same as the operation described above with reference to FIG. Therefore, the same parts as those in FIG. 12 described above are denoted by the same symbols, and description thereof is omitted.

  Next, the operation of the piezoelectric transformer driving circuit according to the first embodiment will be described with reference to FIG.

  FIG. 3 is a waveform diagram showing operation waveforms of each part of the high-voltage power supply device using the piezoelectric transformer according to the first embodiment.

  Reference numeral 300 denotes a voltage waveform of the signal 121 (FIG. 2) applied to the gate of the FET (switching element) 111. Reference numeral 301 denotes a voltage waveform appearing at the drain of the FET 111. Reference numeral 302 denotes a current flowing through the inductor 112.

  When the voltage indicated by 300 becomes equal to or higher than the threshold voltage of the gate of the FET 111 and the FET 111 is turned on, a current flows through the inductor 112 and the energy of the inductor 112 is accumulated. Next, when the voltage indicated by 300 decreases and the FET 111 is turned off, resonance occurs between the inductor 112 and the capacitor 115 as indicated by 301. By driving the FET 111 so that the on-period of the FET 111 starts when the resonance voltage is 0V, the resonance is efficiently and continuously repeated.

  On the other hand, a current waveform flowing through the inductor 112 during the resonance operation is indicated by 302. If the FET 111 is turned on now, the current flows through the FET 111 through the inductor 112. Subsequently, when the FET 111 is turned off, the current continues to flow so as to charge the capacitor 115 by the inductive action of the inductor 112. Further, after the current flowing through the inductor 112 becomes zero and the voltage appearing at the drain of the FET 111 becomes the maximum, the current regeneration operation is started conversely. As a result, current flows into the power supply Vcc side from the capacitor 115 and a regenerative diode (not shown) in the FET 111. Thus, the piezoelectric transformer 101 is vibrated by applying a voltage sufficiently boosted by the resonance operation, and generates a high voltage on the secondary side.

  Next, the pyroelectric effect when the power supply circuit board of the high voltage power supply device shown in FIG. 2 is mounted will be described. In FIG. 2, an arrow A indicates the transport direction when the substrate including the power supply circuit portion surrounded by the dotted line portion is flow-mounted. Although FIG. 2 shows a power supply circuit configuration having two drive circuits, the number of drive circuits is not limited to two, and it can be provided according to the required number of voltage outputs and arranged on one substrate. Also, other circuits other than the drive circuit can be arranged on the same substrate as the substrate on which the drive circuit is mounted.

  A high voltage power supply device including the piezoelectric transformer 101 and its driving circuit is placed in a solder flow tank when each component is automatically mounted on a circuit board. At this time, heat is applied to the piezoelectric transformer 101 and the polarization balance on the surface of the piezoelectric transformer is lost. When the polarization balance is lost, a pyroelectric charge amount Qconst is generated between the primary side terminals of the piezoelectric transformer 101. This pyroelectric charge amount Qconst is a charge amount depending on the length and thickness of the piezoelectric transformer 101 and varies depending on the shape of the piezoelectric transformer 101. This pyroelectric charge amount Qconst is Qconst = C0 × V0 based on a generated voltage V0 when a heat equivalent to the temperature profile of the solder flow tank is applied to the piezoelectric transformer alone and a primary side parasitic capacitance C0 of the piezoelectric transformer 101Y. Can be sought.

  With reference to FIGS. 4-7, the voltage rise which generate | occur | produces between the terminals of the piezoelectric transformer 101 when passing a solder flow tank is demonstrated.

  4 and 5, as a comparative explanation for explaining the effect based on the configuration of the first embodiment, the case of the conventional high-voltage power supply device (FIG. 12) not provided with the capacitor 120 as shown in FIG. I will explain it.

  FIG. 4 is a diagram showing a specific example in which the piezoelectric transformer 101, the resonance capacitor 115, the resonance inductor 112, and the FET 111 are arranged on the substrate 400. Here, the substrate 400 is conveyed in the direction of arrow A in the drawing and enters the solder flow tank, and the substrate 400 is lowered in the solder flow tank and comes into contact with the molten solder from below the substrate.

  FIG. 5 is a diagram for explaining the temperature rise and voltage rise of the piezoelectric transformer when the substrate 400 shown in FIG. 4 is automatically mounted in the solder flow tank.

  In the figure, reference numeral 510 denotes a voltage increase of the primary side terminal of the piezoelectric transformer 101 with respect to the time axis on the horizontal axis. Reference numeral 511 denotes a voltage rise at the primary side terminal of the piezoelectric transformer 101, and the time axis thereof is matched with the voltage rise 510 at the primary side terminal.

  The substrate 400 is conveyed toward the solder flow tank along the time axis. First, at timing 520, the preheating process is entered. Reference numeral 521 denotes a preheating step before being immersed in the solder flow tank. In this step, the temperature of the substrate 400 is gradually raised to prevent a rapid temperature change of the substrate 400 and components to be mounted. By this preheating step 521, a voltage is gradually generated between the primary side terminals of the piezoelectric transformer 101 as indicated by 510. Subsequently, at a timing 522, the preheating process is terminated and the solder flow tank is entered. Further, at timing 523, the piezoelectric transformer 101 is immersed in the solder flow tank. At this time, the temperature of the piezoelectric transformer 101 becomes the highest, and the maximum charge Qconst is generated at both ends of the primary side terminal of the piezoelectric transformer 101.

  The voltage generated at the primary terminal of the piezoelectric transformer 101 is directly applied to the wiring 130 shown in FIG. 4 when the primary terminal comes into contact with the copper foil pattern at the land or through hole by clinch or the like. A voltage generated at the primary terminal and the wiring 130 of the piezoelectric transformer 101 is indicated by 511 in FIG.

  A capacitor 115 for resonance driving is connected to the wiring 130. Here, the voltage V1 generated in the wiring 130 is expressed by the following equation (1). Here, the primary side parasitic capacitance C0 of the piezoelectric transformer 101, the generated charge Qconst of the primary side terminal of the piezoelectric transformer 101, and the capacitance of the capacitor 115 are C1.

V1 = Qconst / (C1 + C0) (1)
Then, at timing 524, the voltage V1 generated in the wiring 130 remains maintained until the other terminal of the primary terminal of the piezoelectric transformer 101 is immersed in the solder flow tank. At timing 524, the other terminal on the primary side of the piezoelectric transformer 101 is immersed in the solder flow tank, so that both terminals on the primary side of the piezoelectric transformer 101 are short-circuited, and the potential V1 is "0". Become.

  Further, when the substrate 400 is pulled out of the solder flow tank at a timing 526 through a period 525 in which the piezoelectric transformer 101 passes while being immersed in the solder flow tank, the above-described short circuit between both terminals is released. At this time, a voltage is generated again at the primary side terminal of the piezoelectric transformer 101. This voltage gradually decreases as the heat of the piezoelectric transformer 101 cools.

  In the process described above, the voltage V 1 generated in the wiring 130 is applied between the source and drain of the FET 111. This voltage V 1 is lower than the pyroelectric voltage V 0 generated by the piezoelectric transformer 101 alone due to the capacitance C 1 of the capacitor 115. However, this capacitor 115 is provided for the resonance operation, and its capacitance C1 is specifically a value of about several hundred pF, and cannot play the role of sufficiently reducing the voltage. For this reason, the voltage V1 becomes a high voltage and may exceed the withstand voltage between the drain and source of the FET 111, thereby possibly destroying the FET 111.

  Next, with reference to FIG.6 and FIG.7, the circuit structure of the high voltage power supply device which concerns on 1st Embodiment, and its effect are demonstrated. A feature of the high voltage power supply according to the first embodiment is the presence of the capacitor 120 described above with reference to FIG. The capacitor 120 is inserted between the power supply line of the inductor 112 and the ground. Further, the capacitance C2 of the capacitor 120 is characterized by a sufficiently large value with respect to the primary side parasitic capacitance C0 of the piezoelectric transformer 101.

  FIG. 6 is a diagram showing an example of a specific arrangement of the piezoelectric transformer, the resonance capacitor, the resonance inductor, and the switching FET on the substrate 401 of the drive circuit of the high voltage power supply device according to the first embodiment of the present invention.

  The piezoelectric transformer 101, the resonance capacitor 115, the resonance inductor 112, and the FET 111 have the same configuration as shown in FIG.

  FIG. 7 is a diagram for explaining the temperature rise and voltage rise of the piezoelectric transformer when the substrate 401 of FIG. 6 is conveyed in the direction of arrow A and enters the solder flow mounting process from preheating. In FIG. 7, as in FIG. 5, the voltage generated at the primary terminal of the piezoelectric transformer 101 is applied to the wiring 130 in contact with the copper foil pattern at the land or through hole by clinch or the like. Is done. In FIG. 7, portions common to FIG. 5 are denoted by the same symbols.

  Reference numeral 712 denotes a voltage generated at the primary side terminal of the piezoelectric transformer 101 and the wiring 130. Reference numeral 521 denotes a preheating step, during which a voltage similar to that shown in FIG. Subsequently, the substrate 401 is transported to the solder flow tank, and before the piezoelectric transformer 101 contacts the solder in the solder flow tank at timing 523, the capacitor 120 and the inductor 112 are immersed in the solder flow tank at timing 527, and the copper foil is removed. Connected to the pattern. At the timing 527, a path is established in which the charge generated at the primary side terminal of the piezoelectric transformer 101 is charged to the capacitor 120 via the inductor 112. Thereby, the voltage generated in the wiring 130 is reduced.

  Accordingly, when the piezoelectric transformer 101 is immersed in the solder flow bath at the timing 523, the voltage V2 that rises due to the pyroelectric effect is expressed by the following equation (2), where C2 is the capacitance of the capacitor 120Y.

V2 = Qconst / (C2 + C1 + C0) (2)
Thus, this voltage V2 is applied to the FET 111. Here, the voltage V2 needs to be lower than the maximum rated voltage Vdss between the drain and source of the FET 111. That is, the necessary capacitance C2 of the capacitor 120 needs to satisfy the condition of the expression (3).

C2> (Qconst / Vdss) -C1-C0 (3)
Generally, it is represented by C2> (Q / V) -C1-C0.

  When the capacitance C2 of the capacitor 120 satisfies this condition, the voltage V2 that rises due to the pyroelectric effect becomes equal to or lower than the maximum rated voltage between the drain and source of the FET 111.

  As is apparent from a comparison between FIG. 5 and FIG. 7, in the high voltage power supply device according to the first embodiment, the voltage V 2 generated at the primary side terminal of the piezoelectric transformer 101 is Compared to the voltage V1, it is greatly reduced. As a result, it is possible to prevent destruction of the components of the drive circuit during automatic mounting of the FET 111 by the solder flow bath.

  In the arrangement configuration described with reference to FIG. 6, only the maximum rated voltage between the source and the drain of the FET 111 is targeted.

  FIG. 8 is a diagram illustrating a specific arrangement example of the piezoelectric transformer, the resonance capacitor, the resonance inductor, and the switching FET on the substrate 801 of the drive circuit of the high-voltage power supply device as another example of the first embodiment. In FIG. 8, the same parts as those in FIG. 6 are indicated by the same symbols.

In the arrangement shown in FIG. 8, the gate and drain of the FET 111 are short-circuited first in the order of entry into the solder flow bath. In this case, a voltage V 2 that rises due to the pyroelectric effect is applied between the gate and source of the FET 111. Therefore, in order to prevent the breakdown of the FET 111, the voltage V2 needs to be lower than the maximum rated voltage Vgss between the gate and the source of the FET 111. That is, the required capacitance C2 of the capacitor 120 needs to satisfy the condition of the following formula (4): C2> (Qconst / Vgss) −C1−C0 ... Formula (4)
By doing so, the voltage V2 that rises due to the pyroelectric effect is equal to or lower than the maximum rated voltage between the gate and the source of the FET 111, and it is possible to prevent the FET 111 from being destroyed during automatic mounting by the solder flow bath.

  Next, the capacitance C2 of the capacitor 120 will be described using specific numerical values.

  Now, the generated voltage of the piezoelectric transformer alone at a temperature of about 260 ° C. during automatic mounting in the solder flow tank is set to 900V. The primary parasitic capacitance of this piezoelectric transformer is 500 pF, the capacitance of the resonance capacitor is 470 pF, and the maximum rated voltage of the gate-source voltage of the FET is 30V. The capacitance C2 of the capacitor 120 at this time must satisfy the condition of the following formula (5).

C2> (Qconst / Vgss) -C1-C0
> (900V × 500pF / 30) -470pF-500pF
> 0.014 μF (5)
From this, it can be seen that the capacitor 120 needs to have a capacitance of 0.014 μF or more in order to prevent the FET 111 from being destroyed.

  As described above, the drive circuit of the high voltage power supply apparatus according to the first embodiment includes the piezoelectric transformer 101, the voltage controlled oscillator 110, and the FET 111 that performs switching driving according to the frequency of the frequency signal output from the voltage controlled oscillator 110. And have. Furthermore, a capacitor 115 and an inductor 112 are provided in which a parallel resonance circuit is formed so as to perform a resonance operation by the switching operation of the switching element. In addition, a power supply side terminal connected to the inductor 112 and a pyroelectric voltage reducing capacitor 120 connected between the grounds are provided. The capacitor 120 and the inductor 112 are arranged on the substrate so as to be immersed in the solder flow before the piezoelectric transformer 101 during automatic mounting using the solder flow tank of the piezoelectric transformer 101. Thereby, the voltage rise by the pyroelectric effect of the piezoelectric transformer 101 which generate | occur | produces at the time of automatic mounting using a solder flow tank can be reduced.

  Further, in the first embodiment, the capacitance of the capacitor 120 is set to a value that allows selection of the capacitor and the switching element that are optimal for the power supply device. As a result, automatic mounting by the solder flow tank is possible while reliably preventing the FET as a switching element from being destroyed.

  This eliminates the need for manual operation such as soldering of the piezoelectric transformer, thereby reducing the mounting cost and improving the reliability of the parts after automatic mounting by the solder flow.

The arrangement of the circuit elements (components) shown in FIGS. 6 and 8 according to the first embodiment is merely an example, and the present invention is not limited to this. However, in a board that performs automatic mounting by solder flow, mounting the capacitor 120 and the inductor 112 so as to be immersed in the solder flow before the piezoelectric transformer 101 is an important component of this embodiment.
[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described.

  FIG. 9 is a diagram illustrating the configuration of a piezoelectric transformer drive circuit in the high-voltage power supply device according to the second embodiment of the present invention. In FIG. 9, the same parts as those in FIG. 2 are denoted by the same symbols, and the description thereof is omitted.

  Compared with the drive circuit of the high voltage power supply device according to the first embodiment described above, the difference is that the parallel resonance capacitor 115 of FIG. 2 does not exist. Here, as a resonance circuit, the parasitic capacitance of the piezoelectric transformer 101 is used as a resonance capacitor. Even in the case of this configuration, as in the first embodiment, it is arranged on the substrate 1001 as shown in FIG. 10, and the capacitance C2 of the capacitor 120 is determined by the following equation (5).

C2> (Qconst / Vgss) -C0 (5)
FIG. 10 is a diagram showing a specific example in which a piezoelectric transformer, a resonance capacitor, a resonance inductor, and a switching FET are arranged on the substrate of the drive circuit of the high voltage power supply device according to the second embodiment. In FIG. 10, portions common to FIG. 6 are denoted by the same symbols.

  The capacitor 120 having the capacity calculated by the above equation (5) is connected between the power supply Vcc and the ground. As a result, as shown in FIG. 10, the capacitor 120 and the inductor 112 are immersed in the solder flow before the piezoelectric transformer 101 during automatic mounting using the solder flow bath.

  That is, as in the case of FIG. 6 described above, the capacitor 120 and the inductor 112 are immersed in the solder flow bath and connected to the copper foil pattern. As a result, a path is established in which the charge generated at the primary terminal of the piezoelectric transformer 101 is charged to the capacitor 120 via the inductor 112. Thus, the voltage generated in the wiring 130 is reduced.

As described above, according to the second embodiment, it is possible to select a capacitive element in consideration of a withstand voltage of a driving circuit component of a piezoelectric transformer in which a switching element that is a semiconductor element such as an FET is used. As a result, it is possible to perform automatic mounting by a solder flow while reliably preventing destruction of used parts. As a result, it is possible to prevent the component from being destroyed during automatic mounting using the solder flow tank of the FET.
[Third Embodiment]
The third embodiment of the present invention will be described below. Here, unlike the first embodiment, a case where the substrate 1101 is reflow mounted will be described.

  FIG. 11 is a diagram illustrating a substrate on which components of a driving circuit of a piezoelectric transformer, which are all configured by surface mount type elements, are arranged as an example of the third embodiment. The numbers in the figure correspond to the same numbers described in FIG. 2 described in the first embodiment.

  In the case of reflow mounting, the terminals of the components mounted on the substrate 1101 with cream solder are connected to each other via the print pattern. Therefore, the arrangement shown in FIG. 11 of the third embodiment is not an important component of the present invention, but is merely described as an example for explanation.

  Further, unlike the first embodiment, the drain and gate of the FET 111 are not short-circuited by solder. Therefore, when determining the capacitance of the capacitor 120, only the maximum rated voltage Vdss between the drain and source of the FET 111 needs to be considered. That is, the capacitance value C2 of the capacitor 120 is as follows, assuming that the charge amount Qconst generated between the primary terminals of the piezoelectric transformer 101, the primary parasitic capacitance of the piezoelectric transformer 101 is C0, and the capacitance of the resonance driving capacitor 115 is C1. (6) is satisfied.

C2> (Qconst / Vdss) -C1-C0 (6)
Thereby, the voltage generated by the pyroelectric effect of the piezoelectric transformer 101 during the reflow mounting becomes equal to or lower than the maximum rated voltage of the FET 111. In this way, reflow mounting can be performed without damaging the FET.

  As described above, the drive circuit of the high voltage power supply device according to the third embodiment has the following configuration. That is, a piezoelectric transformer, a frequency control oscillator, a switching element that is driven to switch by an output signal from the frequency control oscillator, and a capacitor and an inductor that form a parallel resonance circuit so as to perform a resonance operation by the switching operation. Furthermore, it has a capacitor connected between the power supply side terminal connected to the inductor and the ground. And the capacity | capacitance of the capacitor | condenser connected between the power supply side terminal connected to an inductor, and a ground is determined by the above-mentioned Formula (6).

  As a result, it is possible to select the most suitable capacitive element (capacitor) and switching element for the high-voltage power supply device according to this embodiment. Further, reflow mounting is possible while reliably preventing the switching element from being destroyed.

  According to the third embodiment, by providing a capacitive element for reducing a voltage increase due to the pyroelectric effect of the piezoelectric transformer, the voltage applied to the drive circuit component of the piezoelectric transformer even when the substrate is reflow-mounted. Can be reduced. As a result, it is possible to reliably prevent the use parts from being destroyed, leading to the reliability of the apparatus. In addition, there is an effect that cost can be reduced by not performing manual mounting, and that component reliability after reflow mounting can be improved.

It is a figure which shows the specific structural example of the tandem type color laser printer provided with the high voltage power supply device which concerns on this embodiment. It is a circuit diagram which shows the structure of the high voltage power supply device which has a piezoelectric transformer which concerns on 1st Embodiment. It is a wave form diagram which shows the operation | movement waveform of each part of the high voltage power supply device using the piezoelectric transformer which concerns on 1st Embodiment. It is a figure which shows the specific example of arrangement | positioning of the piezoelectric transformer, resonance capacitor, resonance inductor, and switching FET on the board | substrate of the conventional high voltage power supply device. It is a figure explaining the temperature rise and voltage rise of a piezoelectric transformer when the board | substrate shown in FIG. 4 is mounted automatically by a solder flow tank. It is a figure which shows the specific example of arrangement | positioning of the piezoelectric transformer, the capacitor | condenser for resonance, the inductor for resonance, and switching FET in the board | substrate of the high voltage power supply device which concerns on 1st Embodiment. It is a figure explaining the temperature rise and voltage rise of a piezoelectric transformer when the board | substrate of FIG. 6 is conveyed in the direction of the arrow and the automatic mounting process using a solder flow tank is implemented from preheating. It is a figure which shows the other example of specific arrangement | positioning of the piezoelectric transformer, the capacitor | condenser for resonance, the inductor for resonance, and switching FET in the board | substrate of the high voltage power supply device which concerns on 1st Embodiment. It is a block diagram explaining the structure of the high voltage power supply device which concerns on 2nd Embodiment of this invention. It is a figure which shows the specific example of arrangement | positioning of the piezoelectric transformer, the capacitor | condenser for resonance, the inductor for resonance, and switching FET in the board | substrate of the high voltage power supply device which concerns on 2nd Embodiment. It is a figure explaining the board | substrate comprised in the board | substrate of the high-voltage power supply device which concerns on 3rd Embodiment by all the elements of a surface mount type. It is a figure which shows an example of the conventional high voltage power supply circuit using a piezoelectric transformer. It is a figure showing the characteristic of the output voltage with respect to the drive frequency of the piezoelectric transformer of FIG.

Claims (9)

Piezoelectric transformer, frequency-controlled oscillator that generates a frequency signal for driving the piezoelectric transformer, a switching element that is connected to a primary side of the piezoelectric transformer and performs a switching operation according to the frequency signal, and a switching operation by the switching element A high-voltage power supply device having a circuit board having a capacitor and an inductor constituting a parallel resonant circuit that performs a resonant operation by:
The circuit board has a capacitive element connected between the power supply side of the inductor and the ground,
When the circuit board is soldered by the solder flow method, the capacitive element, the inductor, and the piezoelectric transformer are arranged so that the piezoelectric transformer is mounted after the capacitive element and the inductor are mounted. A high-voltage power supply device.   The capacitance C2 of the capacitive element is defined as Q, the amount of pyroelectric charge generated in the piezoelectric transformer when soldered by the solder flow method, C0, the parasitic capacitance of the primary side of the piezoelectric transformer, C1, 2. The high-voltage power supply apparatus according to claim 1, wherein the voltage of the switching element connected to the primary side of the piezoelectric transformer satisfies a condition of C2> Q / V-C0-C1 where V is a withstand voltage. . Piezoelectric transformer, frequency-controlled oscillator that generates a frequency signal for driving the piezoelectric transformer, a switching element that is connected to a primary side of the piezoelectric transformer and performs a switching operation according to the frequency signal, and a switching operation by the switching element A high-voltage power supply device having an inductor for performing resonance operation by
The circuit board has a capacitive element connected between the power supply side of the inductor and the ground,
When the circuit board is soldered by the solder flow method, the capacitive element, the inductor, and the piezoelectric transformer are arranged so that the piezoelectric transformer is mounted after the capacitive element and the inductor are mounted. A high-voltage power supply device.   The capacitance C2 of the capacitive element is defined as Q, the amount of pyroelectric charge generated in the piezoelectric transformer when soldered by the solder flow method, C0, the parasitic capacitance on the primary side of the piezoelectric transformer, and the primary side of the piezoelectric transformer. 4. The high-voltage power supply device according to claim 3, wherein a condition of C2> Q / V-C0 is satisfied, where V is a withstand voltage of the connected switching element.   An image forming apparatus comprising the high voltage power supply device according to claim 1. A circuit board on which an element that outputs high voltage is mounted,
A piezoelectric transformer,
A frequency controlled oscillator for generating a frequency signal for driving the piezoelectric transformer;
A switching element connected to a primary side of the piezoelectric transformer and performing a switching operation according to the frequency signal;
A resonance circuit that performs a resonance operation by a switching operation by the switching element, the resonance circuit including a capacitor and an inductor;
A capacitive element connected between the power supply side of the inductor and the ground;
When the circuit board is soldered by the solder flow method, the capacitive element, the inductor, and the piezoelectric transformer are arranged so that the piezoelectric transformer is mounted after the capacitive element and the inductor are mounted. A circuit board characterized by.   The capacitance C2 of the capacitive element is defined as Q, the amount of pyroelectric charge generated in the piezoelectric transformer when soldered by the solder flow method, C0, the parasitic capacitance of the primary side of the piezoelectric transformer, C1, 7. The circuit board according to claim 6, wherein a voltage of the switching element connected to the primary side of the piezoelectric transformer satisfies a condition of C2> Q / V-C0-C1 where V is a withstand voltage. A circuit board on which an element that outputs high voltage is mounted,
A piezoelectric transformer,
A frequency controlled oscillator for generating a frequency signal for driving the piezoelectric transformer;
A switching element connected to a primary side of the piezoelectric transformer and performing a switching operation according to the frequency signal;
An inductor for performing a resonance operation by a switching operation by the switching element;
A capacitive element connected between the power supply side of the inductor and the ground;
When the circuit board is soldered by the solder flow method, the capacitive element, the inductor, and the piezoelectric transformer are arranged so that the piezoelectric transformer is mounted after the capacitive element and the inductor are mounted. A circuit board characterized by.   The capacitance C2 of the capacitive element is defined as Q, the amount of pyroelectric charge generated in the piezoelectric transformer when soldered by the solder flow method, C0, the parasitic capacitance on the primary side of the piezoelectric transformer, and the primary side of the piezoelectric transformer. 9. The circuit board according to claim 8, wherein when the withstand voltage of the connected switching element is V, the condition of C2> Q / V-C0 is satisfied.

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