JP2011024362A - High-voltage power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-voltage power supply device that suppresses deterioration in drive efficiency of a piezoelectric transformer and widens an output voltage variable range. <P>SOLUTION: The high-voltage power supply device includes a piezoelectric transformer 20, a detecting part 12 for detecting an output voltage or an output current supplied from the piezoelectric transformer 20, and a control switching part 10 that executes switching between drive-voltage control for making the amplitude of a drive voltage of the piezoelectric transformer 20 variable and drive-frequency control for making the frequency of the drive voltage variable according to the output voltage or the output current detected by the detecting part 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high-voltage power supply device.

  In recent years, an image forming apparatus is required to have an tandem structure in order to improve productivity. In the tandem structure, since a high voltage is required for each color, the mounting area of the high-voltage power supply device is increased. In order to reduce the size of the high-voltage power supply device, a piezoelectric transformer may be used. The piezoelectric transformer is driven by applying an alternating voltage between primary electrodes (input electrodes).

Patent Document 1 discloses a technique in which an output voltage stop circuit outputs an output signal based on a comparison between a control signal and a reference voltage, and a voltage control transmitter stops driving of the piezoelectric transformer by the output signal.
JP 2006-340588 A

  An object of the present invention is to provide a high-voltage power supply device capable of suppressing a decrease in driving efficiency of a piezoelectric transformer and widening an output voltage variable range.

  The high-voltage power supply device according to claim 1 includes a piezoelectric transformer, a detection unit that detects an output voltage or an output current from the piezoelectric transformer, and the piezoelectric voltage according to the output voltage or the output current detected by the detection unit. It is characterized by comprising a control switching unit for switching between drive voltage control for changing the amplitude of the drive voltage of the transformer and drive frequency control for changing the frequency of the drive voltage.

  The high-voltage power supply apparatus according to claim 2, wherein the control switching unit performs the driving frequency control when the output voltage or the output current detected by the detection unit is greater than a predetermined first reference signal. Switching is performed so that when the output voltage or the output current is smaller than the first reference signal, switching is performed so that the drive voltage control is performed.

  The high-voltage power supply apparatus according to claim 3, wherein the control switching unit includes the output voltage or the output current detected by the detection unit, a predetermined second reference signal, and a predetermined third reference signal. Switching is performed so that the drive voltage control and the drive frequency control are performed according to the comparison result.

  According to a fourth aspect of the present invention, there is provided a high-voltage power supply apparatus comprising: a piezoelectric transformer; drive voltage control for making the amplitude of the drive voltage of the piezoelectric transformer variable according to an input output voltage target value signal; And a control switching unit for switching to the driving frequency control.

  The high-voltage power supply device according to claim 5, wherein the control switching unit performs switching so that the drive frequency control is performed when the output voltage target value signal is larger than a predetermined first reference signal, and the output voltage When the target value signal is smaller than the first reference signal, switching is performed so that the drive voltage control is performed.

  The high-voltage power supply apparatus according to claim 6, wherein the control switching unit determines the drive voltage according to a comparison result between the output voltage target value signal and a predetermined second reference signal and a predetermined third reference signal. Switching is performed so that the control and the drive frequency control are performed.

  The high-voltage power supply device according to claim 7 is a piezoelectric transformer, drive voltage control for varying the amplitude of the drive voltage of the piezoelectric transformer in accordance with an input control switching signal, and drive for varying the frequency of the drive voltage. And a control switching unit that performs switching with frequency control.

  According to the first aspect of the present invention, it is possible to suppress a decrease in driving efficiency of the piezoelectric transformer and widen the output voltage variable range.

  According to the second aspect of the present invention, it is possible to suppress a decrease in driving efficiency of the piezoelectric transformer and widen the output voltage variable range.

  According to the invention described in claim 3, the responsiveness and stability of the piezoelectric transformer are improved.

  According to the fourth aspect of the present invention, it is possible to suppress a decrease in driving efficiency of the piezoelectric transformer and widen the output voltage variable range.

  According to the fifth aspect of the present invention, it is possible to suppress a decrease in driving efficiency of the piezoelectric transformer and widen the output voltage variable range.

  According to the sixth aspect of the present invention, the response and stability of the piezoelectric transformer are improved.

  According to the seventh aspect of the present invention, it is possible to suppress a decrease in driving efficiency of the piezoelectric transformer and widen the output voltage variable range.

FIG. 1 is a block diagram illustrating the high-voltage power supply device according to the first embodiment. FIG. 2 is a diagram illustrating a circuit configuration example of the high-voltage power supply device according to the first embodiment. FIG. 3 is a flowchart illustrating the operation of the high-voltage power supply device according to the first embodiment. FIG. 4 is a diagram illustrating a relationship between the output voltage or the control voltage, the drive frequency, and the amplitude of the drive voltage in the high-voltage power supply apparatus according to the first embodiment. FIG. 5 is a diagram illustrating the relationship between the driving frequency of the piezoelectric transformer, the step-up ratio, and the driving efficiency. FIG. 6 is a flowchart illustrating the operation of the high-voltage power supply device according to the second embodiment. FIG. 7 is a diagram illustrating the relationship between the output voltage or control voltage, the drive frequency, and the amplitude of the drive voltage in the high-voltage power supply apparatus according to the second embodiment. FIG. 8 is a block diagram illustrating the high-voltage power supply device according to the third embodiment. FIG. 9 is a flowchart illustrating the operation of the high-voltage power supply device according to the third embodiment. FIG. 10 is a flowchart illustrating the operation of the high-voltage power supply device according to the fourth embodiment. FIG. 11 is a block diagram illustrating a high-voltage power supply device according to the fifth embodiment. FIG. 12 is a flowchart illustrating the operation of the high-voltage power supply device according to the fifth embodiment.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a high-voltage power supply device according to the first embodiment. Although FIG. 1 shows an example of a positive output power source, the gist is the same for a negative output power source. With reference to FIG. 1, the structure of a high voltage power supply device will be described.

  As shown in FIG. 1, a voltage control unit 4 and a frequency control unit 6 are provided on the primary side of the piezoelectric transformer 20, and the voltage control unit 4 and the frequency control unit 6 are connected to a control switching unit 10. Yes. On the secondary side, a rectifying / smoothing unit including diodes 26 and 28 and a capacitor 30 is provided. Further, the input internal capacitances of the coil 16, the capacitor 18, and the piezoelectric transformer 20 form an LC resonance circuit.

  The output voltage of the piezoelectric transformer 20 is rectified and smoothed by the diodes 26 and 28 and the capacitor 30 and output to the output terminal 32. Further, the output voltage is input to the control switching unit 10 via the detection unit 12. A reference signal is input to the control switching unit 10, and the other end of the control switching unit 10 is connected to the voltage control unit 4 and the frequency control unit 6. The control switching unit 10 switches between the control by the voltage control unit 4 and the control by the frequency control unit 6 according to the output voltage from the piezoelectric transformer 20. A power supply voltage is supplied to the voltage control unit 4 from the terminal 2, and an output of the voltage control unit 4 is connected to one of the resistor 22, the capacitor 18, and the primary electrode of the piezoelectric transformer 20 via the coil 16. The output of the frequency control unit 6 is connected to the gate of a switch 14 that is, for example, a MOSFET. The drain of the switch 14 is connected to one of the primary electrodes of the piezoelectric transformer 20, and the source is grounded via a resistor 24. Similarly, the other primary electrode of the piezoelectric transformer 20, the capacitor 18, and the resistor 22 are grounded.

  The voltage control unit 4 controls the amplitude of the drive voltage input to the piezoelectric transformer 20 in accordance with an input control signal (not shown). The frequency control unit 6 switches the switch 14 in response to an input control signal (not shown), and the DC voltage output from the voltage control unit is subjected to LC resonance by the input internal capacitance of the coil 16, the capacitor 18, and the piezoelectric transformer 20. AC voltage is generated. The generated AC voltage (drive voltage) is input to the piezoelectric transformer 20. That is, the frequency control unit 6 controls the frequency of the drive voltage (drive frequency).

  FIG. 2 is a diagram illustrating a circuit configuration example of the high-voltage power supply device. The circuit configuration will be described with reference to FIG.

  As shown in FIG. 2, the voltage control unit 4 includes a transistor 40, resistors 42 and 44, and a Zener diode 46, and controls the amplitude of the driving voltage of the piezoelectric transformer 20 by operating the transistor 40 as a dropper. The power supply voltage Vcc is input to the resistor 42 and the emitter of the transistor 40.

  The frequency control unit 6 includes resistors 52, 54, 56, and 58, a capacitor 62, an operational amplifier 60, and a MOSFET 64. An output signal from the piezoelectric transformer 20 is input to the inverting input terminal (− terminal) of the operational amplifier 60, and a reference voltage for circuit operation is input from the terminal 50 to the non-inverting input terminal (+ terminal). The output terminal of the operational amplifier 60 is connected to the gate of the MOSFET 64. The source of the MOSFET 64, the resistor 58 and the capacitor 62 are grounded, and the drain of the MOSFET 64 is connected to the non-inverting input terminal (+ terminal) of the operational amplifier 70.

  When the non-inverting input terminal (+ terminal) voltage of the operational amplifier 60 is lower than the inverting input terminal (−terminal) voltage of the operational amplifier 60, a charging current flows through the capacitor 62, and the non-inverting input terminal voltage of the operational amplifier 60 increases. When the non-inverting input terminal voltage of the operational amplifier 60 exceeds the inverting input terminal voltage, the output of the operational amplifier 60 becomes HIGH, and the MOSFET 64 is turned on. Then, the charge accumulated in the capacitor 62 due to the charging current is discharged through the MOSFET 64, and the non-inverting input terminal voltage of the operational amplifier 60 decreases. With the above operation, the non-inverting input terminal voltage of the operational amplifier 60 changes in a triangular wave shape, and the frequency of the triangular wave becomes the frequency of the drive voltage input to the piezoelectric transformer 20.

  The control switching unit 10 includes an operational amplifier 80, a capacitor 78, a resistor 82, and Zener diodes 74 and 76. An output signal from the piezoelectric transformer 20 is input to the non-inverting input terminal (+ terminal) of the operational amplifier 80 via the detection unit 12, and a reference signal is input to the inverting input terminal (− terminal) from the terminal 8 via the resistor 82. Is done. The output terminal of the operational amplifier 80 is connected to the frequency control unit 6 and the non-inverting input terminal (+ terminal) of the operational amplifier 70 through the Zener diode 74 and the resistor 66, and is connected to the voltage control unit 4 through the Zener diode 76 and the resistor 44. The transistor 40 is connected to the base.

  Next, the operation of the high voltage power supply device will be described. FIG. 3 is a flowchart showing the operation of the high-voltage power supply device, and FIG. 4 is a diagram showing the relationship between the output voltage or control voltage (described later), the drive frequency and the amplitude of the drive voltage in the high-voltage power supply device. In the first embodiment, the horizontal axis in FIG. 4 represents the output voltage, and the vertical axis represents the drive frequency and the amplitude of the drive voltage.

  As shown in FIG. 3, first, a drive voltage is input to the primary terminal of the piezoelectric transformer 20 (step S10).

  The piezoelectric transformer 20 boosts and outputs the drive voltage at a boost ratio corresponding to the frequency (drive frequency) of the input drive voltage (step S11). The step-up ratio is the ratio between the amplitude of the output voltage of the piezoelectric transformer and the amplitude of the drive voltage.

  The control switching unit 10 compares the output voltage Vout from the piezoelectric transformer 20 detected by the detection unit 12 with a predetermined first reference signal voltage (reference voltage) V1, and determines whether Vout is smaller than V1. (Step S12).

  In the case of Yes, it progresses to step S13. As illustrated in FIG. 4, the control switching unit 10 performs switching so that the voltage control unit 4 performs control to change the amplitude of the drive voltage. At this time, the drive frequency is controlled to be constant (f2) by the frequency controller 6.

  In No, it progresses to step S14. As shown in FIG. 4, the control switching unit 10 performs switching so that the frequency control unit 6 performs control to make the drive frequency variable. At this time, the drive frequency is swept between f1 and f2. In addition, the amplitude of the drive voltage is constant.

  After steps S13 and S14, the process returns to step S10. As described above, in the high-voltage power supply device according to the first embodiment, if the output voltage Vout is smaller than the reference voltage V1, the voltage control unit 4 performs control to change the amplitude of the drive voltage (drive voltage control). On the other hand, if the output voltage Vout is greater than the reference voltage V1, the frequency control unit 6 performs control to change the drive frequency (drive frequency control). That is, the control switching unit 10 performs switching between drive voltage control and drive frequency control in accordance with the output voltage Vout from the piezoelectric transformer 20 detected by the detection unit 12.

  Here, the characteristics of the piezoelectric transformer will be described. FIG. 5 is a diagram illustrating the relationship between the driving frequency of the piezoelectric transformer, the step-up ratio, and the driving efficiency. The horizontal axis represents the drive frequency, and the vertical axis represents the boost ratio and drive efficiency. A solid line represents the boost ratio, and a broken line represents the drive efficiency.

  As shown in FIG. 5, the boost ratio increases near the resonance frequency f0 and peaks at the resonance frequency f0. Accordingly, the step-up ratio decreases at a frequency far away from the resonance frequency f0. Further, as indicated by hatching in the figure, the piezoelectric transformer 20 has a spurious region in which the monotonicity of the step-up ratio is not established, and the response and stability of the output voltage are reduced in this region. In general, the driving efficiency exhibits a peak in the frequency f1 to f2, that is, in the vicinity of the resonance frequency f0.

  On the other hand, in the drive voltage control method for controlling the input voltage to the piezoelectric transformer, the amplitude of the output voltage of the piezoelectric transformer is proportional to the amplitude of the drive voltage if the drive frequency is constant. In the drive voltage control, for example, a dropper such as a transistor is used to reduce the amplitude of the drive voltage. Therefore, a power loss occurs, and the power loss increases as the input voltage increases.

  As shown in FIG. 4, according to the first embodiment, frequency control is performed in a region where the driving efficiency of the piezoelectric transformer 20 is high by setting the range in which the frequency control unit 6 sweeps the driving frequency to f1 to f2. It becomes. That is, the drive efficiency of the piezoelectric transformer 20 is improved as compared with the case where the control is performed only with either the drive voltage control or the drive frequency control. Further, by setting the upper limit of the sweep frequency to the frequency f2 not included in the spurious region, the responsiveness and stability of the piezoelectric transformer 20 are improved as compared with the case where the upper limit of the sweep frequency is not provided.

  As shown in FIG. 4, in the region where the amplitude of the drive voltage is higher than V1, drive frequency control is performed, so that an increase in power loss due to the dropper is suppressed. Therefore, the output voltage variable range is widened.

  In addition, since the output detection voltage of the piezoelectric transformer 20 is input to the control switching unit 10 and switching is performed, it is not necessary to consider variations in the driving characteristics of the piezoelectric transformer 20, and the driving frequency control is performed in an optimum state.

  The second embodiment is an example in which the control is switched according to the comparison result between the output voltage or output current of the piezoelectric transformer and the second reference signal and the third reference signal which are two reference signals. The configuration of the high-voltage power supply device is the same as that shown in FIGS. FIG. 6 is a flowchart illustrating the operation of the high-voltage power supply device according to the second embodiment. FIG. 7 is a diagram illustrating a relationship between an output voltage or a control voltage (described later), a drive frequency, and an amplitude of the drive voltage in the high-voltage power supply device according to the second embodiment. In FIG. 7, the horizontal axis represents the output voltage, and the vertical axis represents the drive frequency and the amplitude of the drive voltage. When the second reference voltage is V2 and the third reference voltage is V3, V2 <V3. First, the operation of the high-voltage power supply device will be described with reference to FIG. 6, but the description of steps S10 and S11 described in the first embodiment will be omitted.

  As shown in FIG. 6, the control switching unit 10 determines whether the output voltage Vout is greater than the second reference voltage V2 (step S15).

  In No, it progresses to Step S16. As shown in FIG. 7, the control switching unit 10 performs switching so that drive voltage control is performed. At this time, the driving frequency is constant at f2 as in the first embodiment.

  In the case of Yes, it progresses to step S17. The control switching unit 10 determines whether the output voltage Vout is smaller than the third reference voltage V3.

  If No in step S17, the process proceeds to step S18. As shown in FIG. 7, the control switching unit 10 performs switching so that drive frequency control is performed. At this time, the lower limit of the drive frequency is f1, as in the first embodiment. In addition, the amplitude of the drive voltage is constant.

  If Yes in step S17, the process proceeds to step S19. As shown in FIG. 7, the control switching unit 10 performs switching so that drive voltage control and drive frequency control are performed. After steps S16, 18 and 19, the process returns to step S10.

  According to the second embodiment, like the first embodiment, the driving efficiency of the piezoelectric transformer 20 is improved and the output voltage variable range is widened. In addition, the responsiveness and stability of the high-voltage output are improved by variably controlling the driving voltage and the driving frequency simultaneously in the range of V2 to V3.

  In the first and second embodiments, the detection unit 12 detects the output voltage of the piezoelectric transformer 20 and the control switching unit 10 compares it with the reference voltage. However, the detection unit 12 detects the output current, and the control switching unit 10 It may be compared with the current of the reference signal.

  The third embodiment is an example in which the control switching unit 10 switches control according to the comparison result between the output voltage target value signal and the reference signal. FIG. 8 is a block diagram illustrating the high-voltage power supply device according to the third embodiment, and FIG. 9 is a flowchart illustrating the operation of the high-voltage power supply device.

  As shown in FIG. 8, the output signal from the piezoelectric transformer 20 is not input to the control switching unit 10, and the output voltage target value signal is input from the terminal 9. The control switching unit 10 performs switching according to the output voltage target value signal. The description of the same configuration as that already described in FIG. 2 is omitted. Next, the operation of the high-voltage power supply device will be described with reference to FIG.

  As shown in FIG. 9, the output voltage target value signal is input to the control switching unit 10 (step S10).

  The control switching unit 10 compares the voltage (control voltage) Vtarget of the output voltage target value signal with a predetermined reference voltage V1, and determines whether Vtarget is smaller than V1 (step S20).

  In the case of Yes, it progresses to step S13. As shown in FIG. 4, the control switching unit 10 performs switching so that drive voltage control is performed. In Example 3, the horizontal axis in FIG. 4 represents the control voltage.

  In No, it progresses to step S14. The control switching unit 10 performs switching so that drive frequency control is performed. After steps S13 and S14, the process returns to step S20.

  According to the third embodiment, like the first embodiment, the driving efficiency of the piezoelectric transformer 20 is improved and the output voltage variable range is widened. Moreover, since a detection part becomes unnecessary, the number of parts of a high voltage power supply device is reduced.

  The fourth embodiment is an example in which the control switching unit 10 switches control according to the comparison result between the output voltage target value signal, the second reference signal, and the third reference signal. The configuration of the high-voltage power supply device is the same as that shown in FIG. FIG. 10 is a flowchart illustrating the operation of the high-voltage power supply device according to the fourth embodiment.

  As shown in FIG. 10, it is determined whether the output voltage target value signal Vtarget is larger than the second reference voltage V2 (step S21).

  In No, it progresses to Step S16. As shown in FIG. 7, the control switching unit 10 performs switching so that drive voltage control is performed. In Example 4, the horizontal axis in FIG. 7 represents the control voltage.

  In the case of Yes, it progresses to step S22. It is determined whether the output voltage target value signal Vtarget is smaller than the third reference voltage V3.

  If No in step S22, the process proceeds to step S18. As shown in FIG. 7, the control switching unit 10 performs switching so that drive frequency control is performed.

  If Yes in step S22, the process proceeds to step S19. As shown in FIG. 7, the control switching unit 10 performs switching so that drive voltage control and drive frequency control are performed.

  According to the fourth embodiment, the driving efficiency of the piezoelectric transformer 20 is improved as in the second embodiment, and the output voltage variable range is widened. Further, the response and stability of the piezoelectric transformer 20 are improved. As in the third embodiment, since the detection unit is not necessary, the number of parts of the high-voltage power supply device is reduced.

  In the third and fourth embodiments, the control switching unit 10 compares the voltage of the output voltage target value signal with the voltage of the reference signal. However, the current of the output voltage target value signal is compared with the current of the reference signal. Also good.

  The fifth embodiment is an example in which the control switching unit 10 performs switching according to a control switching signal. FIG. 11 is a block diagram showing a high-voltage power supply device according to the fifth embodiment, and FIG. 12 is a flowchart showing an operation of the high-voltage power supply device according to the fifth embodiment.

  As shown in FIG. 11, the output voltage target value signal is input from the terminal 11 to the control switching unit 10. The control switching unit 10 performs switching according to the output voltage target value signal. Next, the operation of the high-voltage power supply device will be described with reference to FIG.

  As shown in FIG. 12, the control switching unit 10 determines whether the control switching signal Vsw is input (step S30).

  In the case of Yes, it progresses to step S13. The control switching unit 10 performs switching so that drive voltage control is performed.

  In No, it progresses to step S14. The control switching unit 10 performs switching so that drive frequency control is performed.

  The above operation is merely an example. Another operation example will be described. For example, when the drive voltage control is being performed, if the control switching signal Vsw is input to the control switching unit 10, the control switching unit 10 performs switching so that the drive frequency control is performed. Further, for example, when the drive frequency control is being performed, if the control switching signal Vsw is input to the control switching unit 10, the control switching unit 10 performs switching so that the drive voltage control is performed. That is, the control switching unit 10 performs switching between driving voltage control and driving frequency control in response to the input of the control switching signal.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Voltage controller 4
Frequency control unit 6
Control switching unit 10
Detection unit 12
Switch 14
Piezoelectric transformer 20

Claims (7)

A piezoelectric transformer,
A detection unit for detecting an output voltage or an output current from the piezoelectric transformer;
Switching between drive voltage control for changing the amplitude of the drive voltage of the piezoelectric transformer and drive frequency control for changing the frequency of the drive voltage according to the output voltage or the output current detected by the detection unit. A high-voltage power supply device comprising: a control switching unit that performs the operation. The control switching unit performs switching so that the drive frequency control is performed when the output voltage or the output current detected by the detection unit is larger than a predetermined first reference signal,
2. The high-voltage power supply device according to claim 1, wherein switching is performed so that the drive voltage control is performed when the output voltage or the output current is smaller than the first reference signal.   The control switching unit is configured to output the driving voltage according to a comparison result between the output voltage or the output current detected by the detection unit and a predetermined second reference signal and a predetermined third reference signal. The high-voltage power supply apparatus according to claim 1, wherein switching is performed so that control and drive frequency control are performed. A piezoelectric transformer,
A control switching unit that switches between driving voltage control for changing the amplitude of the driving voltage of the piezoelectric transformer and driving frequency control for changing the frequency of the driving voltage in accordance with an output voltage target value signal that is input; A high voltage power supply device comprising: The control switching unit performs switching so that the drive frequency control is performed when the output voltage target value signal is larger than a predetermined first reference signal,
5. The high-voltage power supply apparatus according to claim 4, wherein switching is performed so that the drive voltage control is performed when the output voltage target value signal is smaller than the first reference signal.   The control switching unit performs the drive voltage control and the drive frequency control according to a comparison result between the output voltage target value signal and a predetermined second reference signal and a predetermined third reference signal. 5. The high-voltage power supply device according to claim 4, wherein switching is performed so that the A piezoelectric transformer,
A control switching unit that switches between driving voltage control for changing the amplitude of the driving voltage of the piezoelectric transformer and driving frequency control for changing the frequency of the driving voltage in accordance with an input control switching signal; A high-voltage power supply device characterized by:

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