JP2007037312A - Power supply device using piezoelectric transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an output voltage without deteriorating the control accuracy of an output current. <P>SOLUTION: A voltage detection electrode 11 detects an electrostatic induction voltage Vs by an output voltage Vo of a piezoelectric transformer 20. A drive voltage control device 15 controls a drive voltage Vs based on the electrostatic induction voltage Vs. A drive portion 17 supplies the controlled drive voltage Vd to the piezoelectric transformer 20, which transforms the supplied drive voltage Vd and supplies the voltage to a load 90 as the output voltage Vo. The voltage detection electrode 11 detects the electrostatic induction voltage Vs by the output voltage Vo and this operation is repeated. The output voltage Vo is detected indirectly by the voltage detection electrode 11 so that there is no need to use a resistor when detecting the output voltage Vo. Consequently, a current for detecting the output voltage Vo cannot be mixed with the output current Io, so that the output current Vo can be detected without deteriorating the control accuracy of the output current Io. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric transformer technology that transforms an alternating voltage using a resonance phenomenon of a piezoelectric vibrator, and more particularly to a power supply device using the piezoelectric transformer technology.

  In an electrophotographic apparatus such as a copying machine or a printer, a DC bias power source for applying a positive high voltage output and a negative high voltage output is used for a transfer device or the like. This DC bias power source applies, for example, a DC bias current of several μA opposite in polarity to the charged toner to the paper while controlling the constant current, transfers the toner onto the paper, and then cleans the toner adhering to the roller or the like. For this purpose, a DC bias current having a reverse characteristic to that before transfer is applied. As a DC bias power source that can output such positive and negative DC bias currents, a wound transformer has been mainly used.

  However, the winding transformer has a problem in terms of combustibility because an organic substance is used as an insulator. Also, since the DC bias power supply has an extremely small output current value of several μA, the winding transformer needs to be devised in terms of mounting and structure in order to minimize the leakage current.

  In order to compensate for these drawbacks, it is conceivable to form a DC bias power source using a piezoelectric transformer. Since the piezoelectric transformer is made of ceramics and does not require an organic insulator, there is no risk of combustion, and it has excellent characteristics that it can be easily reduced in size and weight. A conventional power supply device using a piezoelectric transformer is disclosed in, for example, Patent Document 1 below.

JP 2003-235255 A

  In a DC bias power source using a piezoelectric transformer, when the output current is controlled at a constant current, the output voltage becomes maximum when there is no load because the constant voltage is maintained by increasing the output voltage when the load resistance increases. . If this is left as it is, the piezoelectric transformer may be damaged by applying excessive mechanical vibration to the piezoelectric transformer. Therefore, it is conceivable to insert a resistor in the output circuit, detect the output voltage, and control the output voltage not to exceed a certain level. At this time, the current flowing through the resistor (hereinafter referred to as “output voltage detection current”) is, for example, 60 μA when the output voltage is 6 kV and the resistance value of the resistor is 100 MΩ.

  However, in the DC bias power supply, the output current flowing through the load is so small as several μA, and the output voltage detection current that is several tens of times the output current is mixed, so that the accuracy in controlling the output current is reduced. Problems arise. For example, when the output voltage detection current flows into the output current detection unit, the output current detection accuracy decreases.

  Furthermore, by feeding back the voltage drop of the resistor provided on the secondary side (output side) of the piezoelectric transformer to the primary side (input side), the insulation between the primary side and the secondary side is impaired. As a result, there arises a problem that, for example, noise affects each other on the primary side and the secondary side.

  Therefore, a first object of the present invention is to provide a power supply device using a piezoelectric transformer that can detect an output voltage without degrading the control accuracy of the output current. A second object of the present invention is to provide a power supply device using a piezoelectric transformer that can improve insulation between the primary side and the secondary side of the piezoelectric transformer.

  A power supply device according to the present invention includes a piezoelectric transformer that transforms an applied drive voltage and supplies it to a load as an output voltage, an output detection unit having voltage detection means for detecting the output voltage of the piezoelectric transformer, and an output detection unit. A drive voltage control unit that controls the drive voltage based on the detected output voltage, and a drive unit that applies the drive voltage controlled by the drive voltage control unit to the piezoelectric transformer are provided. The voltage detection means is a voltage detection electrode that detects an electrostatic induction voltage due to the output voltage of the piezoelectric transformer.

  An electrostatic induction voltage is generated around the piezoelectric transformer due to the output voltage of the piezoelectric transformer. At this time, if the output voltage is high, the electrostatic induction voltage is also high, and if the output voltage is low, the electrostatic induction voltage is low, so that the output voltage and the electrostatic induction voltage have a corresponding relationship. Therefore, the output voltage of the piezoelectric transformer can be indirectly detected by detecting the electrostatic induction voltage around the piezoelectric transformer.

  The voltage detection electrode in the present invention detects an electrostatic induction voltage due to the output voltage of the piezoelectric transformer. The drive voltage control unit controls the drive voltage based on the electrostatic induction voltage. The drive unit applies a controlled drive voltage to the piezoelectric transformer. The piezoelectric transformer transforms the applied drive voltage and supplies it as an output voltage to the load. The voltage detection electrode detects the electrostatic induction voltage due to the output voltage, and the above-described operation is repeated. Thus, since the output voltage is indirectly detected by the voltage detection electrode, it is not necessary to use a resistor when detecting the output voltage. Therefore, since the output voltage detection current and the output current are not mixed, the output voltage can be measured without degrading the control accuracy of the output current.

  The power supply device according to claim 2 is the power supply device according to claim 1, wherein the voltage detection electrode is formed on the printed wiring board on which the piezoelectric transformer is mounted together with the wiring of the printed wiring board.

  Since the voltage detection electrode is formed simultaneously with the wiring of the printed wiring board, it is not necessary to provide a separate process for forming the voltage detection electrode. In addition, since the connection between the voltage detection electrode and the wiring of the printed wiring board is made at the same time when the wiring is formed, a separate process is unnecessary and the structure is simple.

  Alternatively, a piezoelectric transformer may be mounted on one surface of the printed wiring board, and a voltage detection electrode may be formed on the other surface of the printed wiring board so as to face the piezoelectric transformer. At this time, the piezoelectric transformer and the voltage detection electrode are opposed to each other with the printed wiring board interposed therebetween. Therefore, the creeping distance between the piezoelectric transformer and the voltage detection electrode is the distance from the piezoelectric transformer on one side of the printed wiring board to the voltage detection electrode on the other side of the printed wiring board through the peripheral edge of the printed wiring board. From long enough. Therefore, the insulation between the piezoelectric transformer and the voltage detection electrode is good.

  A power supply device according to a third aspect is the power supply device according to the first or second aspect, wherein the drive voltage control unit controls the drive voltage only by the electrostatic induction voltage detected by the voltage detection electrode.

  Since the voltage detection electrode is provided on the primary side, the insulation between the primary side and the secondary side is not impaired even if the voltage detection electrode is provided.

  The power supply device according to claim 4 is the power supply device according to claim 1 or 2, wherein the output detection unit further includes a current detection unit that detects an output current of the piezoelectric transformer, and the drive voltage control unit is the output detection unit. The drive voltage is controlled so that the output voltage detected in step 1 does not exceed the set value and the output current detected by the output detection unit becomes equal to the set value.

  When controlling the output current to be a set value, the output voltage is increased to maintain the set value as the output current decreases. However, when the output voltage becomes excessive, the piezoelectric transformer may be damaged. Therefore, the output voltage is detected by the voltage detection electrode, and control is performed so that the output voltage does not exceed the set value. As described above, since the output voltage can be measured without reducing the control accuracy of the output current, the present invention is suitable for the constant current control of the output current.

  A power supply device according to a fifth aspect is the power supply device according to the fourth aspect, wherein the drive voltage control unit controls the drive voltage by controlling at least one of a frequency of the drive voltage and a duty ratio.

  In general, in frequency control of a piezoelectric transformer, when the frequency is a resonance frequency, the output voltage (output current) and the efficiency are maximized. Generally, in the duty ratio control of the piezoelectric transformer, when the duty ratio is 50%, the output voltage (output current) and the efficiency are maximized. Therefore, by combining these conditions, the maximum value of the output current and efficiency can be obtained in the simultaneous frequency and duty ratio simultaneous control of a general piezoelectric transformer.

  The output voltage (output current) can be lowered regardless of whether the frequency of the drive voltage is higher or lower than the resonance frequency. However, it is preferable to use a higher frequency than the resonance frequency for the following reason. (1) If the output voltage is the same, the high frequency side is more efficient than the low frequency side. (2) When the frequency of the piezoelectric transformer is changed so as to obtain an output voltage exceeding a certain level, a nonlinear phenomenon as shown in FIG. 8 appears. That is, the frequency at which the maximum output voltage is obtained is different between the case where the resonance frequency is approached from the high frequency side and the case where the resonance frequency is approached from the low frequency side. In particular, when scanning from the lower frequency side, a so-called jump phenomenon occurs, and the output voltage change with respect to the frequency change becomes extremely large. Therefore, when scanning from the side higher than the resonance frequency, the output voltage change with respect to the frequency change is small, so that the output voltage can be controlled with high accuracy.

  The power supply device according to claim 6 is the power supply device according to claim 5, wherein the frequency and duty ratio at which the output current is maximum are F1 and D1, respectively, and the frequency and duty ratio at which the output current is minimum are F2 respectively. , D2, the drive voltage control unit brings the frequency and the duty ratio closer to F1 and D1, respectively, if the detected output current is smaller than the set value, and conversely if the detected output current is larger than the set value. The frequency and the duty ratio are made closer to F2 and D2, respectively.

  When the output voltage increases, the output current increases, and when the output voltage decreases, the output current also decreases. Therefore, the output voltage (output current) increases when the frequency of the drive voltage is brought close to F1. Here, when the duty ratio approaches D1, the output voltage (output current) increases. Therefore, the output voltage (output current) further increases when the frequency is close to F1 and the duty ratio is close to D1. On the other hand, when the frequency of the drive voltage is brought close to F2, the output voltage (output current) decreases. Further, when the duty ratio is brought close to D2, the output voltage (output current) decreases. Therefore, the output voltage (output current) is further reduced when the frequency is close to F2 and the duty ratio is close to D2. As described above, the frequency and the duty ratio can be controlled at the same time by making the frequency range and the duty ratio range constant.

  The power supply device according to claim 7 is the power supply device according to claim 5 or 6, wherein the drive voltage control unit includes a frequency control unit that generates a variable frequency triangular wave voltage Vb, and a triangular wave voltage Vb generated by the frequency control unit. And a voltage value variable DC voltage Va, and a duty ratio control unit that determines a duty ratio based on a time when Va <Vb and a time when Va> Vb, and based on an output voltage detected by the output detection unit A voltage control unit that changes at least one of the voltage value of the DC voltage Va and the frequency of the triangular wave voltage Vb, and at least one of the voltage value of the DC voltage Va and the frequency of the triangular wave voltage Vb based on the output current detected by the output detection unit. And a current control unit for changing.

  Here, the time when Va <Vb is the on time, and the time when Va> Vb is the off time. At this time, if the detected output current is lower than the set value, for example, the current control unit lowers the voltage value of the DC voltage Va and lowers the frequency of the triangular wave voltage Vb. Then, the duty ratio approaches 50% by increasing (ON time) / (ON time + OFF time), and the frequency approaches the resonance frequency by increasing (ON time + OFF time). Conversely, if the detected output current is higher than the set value, the current control unit, for example, increases the voltage value of the DC voltage Va and increases the frequency of the triangular wave voltage Vb. Then, the duty ratio is moved away from 50% by decreasing (ON time) / (ON time + OFF time), and the frequency is moved away from the resonance frequency by decreasing (ON time + OFF time).

  On the other hand, if the detected output voltage is lower than the set value, the voltage control unit does not operate. On the other hand, if the detected output voltage is higher than the set value (or if it is about to exceed the set value), the voltage control unit increases the voltage value of the DC voltage Va and increases the frequency of the triangular wave voltage Vb, for example. . Then, the duty ratio moves away from 50% by decreasing (ON time) / (ON time + OFF time), and the frequency moves away from the resonance frequency by decreasing (ON time + OFF time). In this way, the drive voltage control unit controls the frequency and duty used to apply the drive voltage so that the detected output current becomes equal to the set value and the detected output voltage does not exceed the set value. Control the ratio simultaneously.

  A power supply apparatus according to an eighth aspect of the present invention is the power supply apparatus according to any one of the first to seventh aspects, wherein the power supply apparatus is used as a DC bias power supply for an electrophotographic apparatus.

  This DC bias power supply is required to have characteristics that, for example, the output current varies from approximately 0 to several μA, the output voltage varies from several tens of volts to approximately 3 kV, and the load varies from several tens of MΩ to approximately 10 GΩ. The power supply device of the invention is suitable.

  In other words, the present invention forms a pattern (electrode) for detecting the induced voltage on the printed wiring board on which the piezoelectric transformer is mounted, having a certain distance from the conductive portion on the output side of the piezoelectric transformer, and the detection is performed there. The induced voltage is rectified to a DC voltage, and the maximum output voltage is controlled by that voltage. Since it is not in direct contact with the output side of the piezoelectric transformer, it does not affect the load characteristics of the piezoelectric transformer, and since it is detected separately from the output current detection part, accurate constant current control is possible. it can. Further, by detecting the induced voltage at a mechanically fixed position, a stable induced voltage proportional to the output voltage is detected, so that the accuracy of the no-load voltage can be ensured. In this way, in a high voltage power supply device for a piezoelectric transformer that performs control to operate an output current with a constant current in a wide load range, the no-load voltage can be stably controlled.

  According to the power supply device of the present invention, since the output voltage of the piezoelectric transformer is indirectly detected by the electrostatic induction voltage, a resistor for detecting the output voltage can be eliminated, so that the output current control accuracy can be improved. The output voltage can be detected without dropping. Moreover, according to the power supply device which concerns on this invention, there exists the following effect for every claim.

  According to the power supply device of the second aspect, by forming the voltage detection electrode together with the wiring on the printed wiring board on which the piezoelectric transformer is mounted, the voltage detection electrode can be formed simultaneously in the wiring forming process of the printed wiring board. In addition to this, the connection between the voltage detection electrode and the wiring of the printed wiring board is made at the same time when the wiring is formed, so that another process is unnecessary and the structure is simple. Therefore, the complexity of the manufacturing process and structure can be suppressed.

  According to the power supply device of the third aspect, by controlling the drive voltage only by the electrostatic induction voltage, it becomes possible to perform feedback control in the configuration on the primary side, so that insulation between the primary side and the secondary side is possible. Can be improved.

  According to the power supply device of the fourth aspect, the output voltage of the piezoelectric transformer is indirectly detected by the electrostatic induction voltage, so that the output voltage that tends to occur in the constant current control is increased, and the control accuracy of the output current is increased. Control without dropping.

  According to the power supply device of claim 5, by controlling at least one of the frequency and duty ratio of the drive voltage, the drive voltage control with a wide variable range of the output current is realized by combining the frequency control and the duty ratio control. it can.

  The power supply device according to claim 6, wherein the frequency and duty ratio of the driving voltage are set to one of a combination of a frequency and a duty ratio at which a minimum output current is obtained, or a combination of a frequency and a duty ratio at which a maximum output current is obtained. By bringing them closer, an extremely wide output current width can be obtained.

  The power supply device according to claim 7 changes the voltage value of the DC voltage Va and the frequency of the triangular wave voltage Vb based on the difference between the detected output current and the set output current, and compares the DC voltage Va with the triangular wave voltage Vb to compare the frequency and By defining the duty ratio, an extremely wide output current width can be obtained.

  According to the power supply device of the eighth aspect, for example, the characteristics in which the output current changes from almost 0 to several μA, the output voltage changes from several tens of V to about 3 kV, and the load changes from several tens of MΩ to about 10 GΩ. Therefore, it can be suitably used as a DC bias power source for an electrophotographic apparatus.

  FIG. 1 is a block diagram showing an embodiment of a power supply device according to the present invention. Hereinafter, description will be given based on this drawing.

  The power supply device 10 of the present embodiment includes a positive voltage power supply 101 that outputs a positive (plus) DC bias voltage, a negative voltage power supply 102 that outputs a negative (minus) DC bias voltage, a positive voltage power supply 101, and a negative voltage. The output switching part 12 which switches the output with the power supply 102 to either one, and the current detection part 13 which detects the electric current which flows into the load 90 are provided. For example, the output switching unit 12 supplies the input voltage Vin only to the positive voltage power supply 101 if the switching signal S is at the H level, and supplies the input voltage Vin only to the negative voltage power supply 102 if the switching signal S is the L level. .

  The positive voltage power source 101 transforms the applied drive voltage Vd and supplies it to the load 90 as an output voltage Vo, and a voltage detection unit 14 having a voltage detection electrode 11 that detects the output voltage Vo of the piezoelectric transformer 20. A drive voltage controller 15 that controls the drive voltage Vd based on the output voltage Vo detected by the voltage detector 14, and a drive unit 16 that applies the drive voltage Vd controlled by the drive voltage controller 15 to the piezoelectric transformer 20. It is equipped with. The drive unit 16 includes an FET 161, an inductor 162, a capacitor 163, and the like.

  The driving voltage control unit 15 compares the triangular wave voltage Vb generated by the frequency control unit 60 with the frequency control unit 60 that generates the variable frequency triangular wave voltage Vb, and the voltage value variable DC voltage Va, and Va <Vb. A duty ratio controller 70 that determines a duty ratio based on a certain time and a time Va> Vb, and a voltage value of the DC voltage Va and a frequency of the triangular wave voltage Vb based on the output voltage Vo detected by the voltage detector 14. A voltage control unit 40 that changes at least one of the voltages and a current control unit 50 that changes at least one of the voltage value of the DC voltage Va and the frequency of the triangular wave voltage Vb based on the output current Io detected by the current detection unit 13 are provided. .

  An FV conversion unit 17 and a reference voltage unit 18 are attached to the input side of the positive voltage power source 101. For example, the F-V converter 17 receives a control signal PWM corresponding to a set value of the output current Io. The reference voltage unit 18 outputs a reference voltage Vr corresponding to the set value of the output current Io to the drive voltage control unit 15. Thus, the drive voltage control unit 14 controls at least one of the frequency F and the duty ratio Du of the drive voltage Vd so that the output current Io detected by the current detection unit 13 becomes equal to the set value. At the same time, the drive voltage control unit 14 controls at least one of the frequency F and the duty ratio Du of the drive voltage Vd so that the output voltage Vo detected by the voltage detection unit 14 does not exceed a separately set value. . Note that the FV conversion unit 17 and the reference voltage unit 18 are unnecessary if the reference voltage Vr is always constant, for example.

  A high-voltage rectifying unit 191 is attached to the output side of the positive voltage power supply 101. The high voltage rectifier 191 rectifies the output voltage Vo of the piezoelectric transformer 20 into a positive DC voltage and applies it to the load 90. The negative voltage power supply 102 has substantially the same configuration as the positive voltage power supply 101 except for the high voltage rectification unit 192. The high voltage rectifier 192 rectifies the output voltage Vo of the piezoelectric transformer 20 into a negative DC voltage and applies it to the load 90. In the positive voltage power supply 101 and the negative voltage power supply 10, the same components are denoted by the same reference numerals.

  The piezoelectric transformer 20 is provided with primary electrodes 22 and 23 and a secondary electrode 24 on a piezoelectric vibrating body 21, the primary side is polarized in the thickness direction (vertical direction in FIG. 1), and the secondary side in the length direction (FIG. 1). It is polarized in the horizontal direction). The primary electrodes 22 and 23 are opposed to each other with the piezoelectric vibrator 21 interposed therebetween. The piezoelectric vibrating body 21 is made of piezoelectric ceramics such as PZT and has a plate shape (cuboid shape). In the longitudinal direction of the piezoelectric vibrator 21, primary electrodes 22 and 23 are provided from one end to, for example, half of the length, and a secondary electrode 24 is provided at the other end. When the drive voltage Vd having the natural resonance frequency fr determined by the length dimension is input to the primary side, strong mechanical vibration is caused by the inverse piezoelectric effect, and a high output voltage Vo corresponding to the vibration is output from the secondary side by the piezoelectric effect. . The output voltage Vo is applied to the load 90.

  Next, the operation and effect of the power supply device 10 will be described. An electrostatic induction voltage Vs is generated around the piezoelectric transformer 20 by the output voltage Vo of the piezoelectric transformer 20. At this time, if the output voltage Vo is high, the electrostatic induction voltage Vs also becomes high, and if the output voltage Vo is low, the electrostatic induction voltage Vs also becomes low. Therefore, the output voltage Vo and the electrostatic induction voltage Vs have a correspondence relationship. Therefore, the voltage detection electrode 11 can indirectly detect the output voltage Vo of the piezoelectric transformer 20 by detecting the electrostatic induction voltage Vs around the piezoelectric transformer 20.

  Thus, the voltage detection electrode 11 detects the electrostatic induction voltage Vs due to the output voltage Vo of the piezoelectric transformer 20. The drive voltage control unit 15 controls the drive voltage Vs based on the electrostatic induction voltage Vs. The drive unit 17 applies the controlled drive voltage Vd to the piezoelectric transformer 20. The piezoelectric transformer 20 transforms the applied drive voltage Vd and supplies it to the load 90 as the output voltage Vo. The voltage detection electrode 11 detects the electrostatic induction voltage Vs due to the output voltage Vo, and the above-described operation is repeated. At this time, since the output voltage Vo is indirectly detected by the voltage detection electrode 11, it is not necessary to use a resistor when detecting the output voltage Vo. Therefore, since the current for detecting the output voltage Vo cannot be mixed in the output current Io, the output voltage Vo can be detected without reducing the control accuracy of the output current Io.

  Further, the drive voltage control unit 15 may control the drive voltage Vd only by the electrostatic induction voltage Vs detected by the voltage detection electrode 11, that is, without providing the current detection unit 13. In this case, since the voltage detection electrode 11 is provided on the primary side of the piezoelectric transformer 20, the insulation between the primary side and the secondary side of the piezoelectric transformer 20 is not impaired even if the voltage detection electrode 11 is provided.

  2 shows an example of the voltage detection electrode in the power supply device of FIG. 1, FIG. 2 [1] is a plan view of the voltage detection electrode, and FIG. 2 [2] is a cross-sectional view taken along the line II in FIG. The transformer side is shown above). Hereinafter, a description will be given based on FIG. 1 and FIG.

  The piezoelectric transformer 20 is sealed in a resin case 25. The voltage detection electrode 11 is formed together with the wiring 31 on the printed wiring board 30 on which the piezoelectric transformer 20 is mounted.

  The printed wiring board 30 is a general one composed of an insulating plate 32, a conductor film 33, an insulating film 34, and the like. The insulating plate 32 and the insulating film 34 are made of synthetic resin, for example. The conductor film 33 is, for example, a copper foil, and is processed into a predetermined shape to become the wiring 32 or the voltage detection electrode 11. Although not shown, a conductive film and an insulating film are provided on the surface 35 of the insulating plate 32, the components (not shown) of the piezoelectric transformer 20 and the power supply device 10 are mounted, and wiring (not shown) is also formed. ing. Wirings 32 and voltage detection electrodes 11 are formed on the back surface 36 of the insulating plate 32, and these are covered with an insulating film 34. However, in FIG. 2 [1], the insulating film 34 is omitted.

  Next, a method for forming the wiring 32 and the voltage detection electrode 11 on the printed wiring board 30 will be described. First, an insulating plate 32 having a conductor film 33 formed on the entire surface is prepared. Then, the conductor film 33 is processed into a predetermined shape using, for example, photolithography and etching, and the wiring 32 and the voltage detection electrode 11 are obtained. Finally, the wiring 32 and the voltage detection electrode 11 are covered with an insulating film 34 except for the soldered portion of the wiring 32.

  Thus, since the voltage detection electrode 11 is formed simultaneously with the wiring 31 of the printed wiring board 30, it is not necessary to provide another process for forming the voltage detection electrode 11. In addition, since the connection between the voltage detection electrode 11 and the wiring 31 of the printed wiring board 30 is made at the same time when the wiring 31 is formed, a separate process is unnecessary and the structure is simple. Therefore, according to the power supply device 10 of the present embodiment, it is possible to suppress the complexity of the manufacturing process and the structure while having a configuration capable of self-oscillation without inhibiting the vibration of the piezoelectric transformer 20.

  In the present embodiment, the piezoelectric transformer 20 is mounted on one surface of the printed wiring board 30, and the voltage detection electrode 11 is formed on the other surface of the printed wiring board 30 so as to face the piezoelectric transformer 20. That is, the piezoelectric transformer 20 and the voltage detection electrode 11 are opposed to each other with the printed wiring board 30 interposed therebetween. Therefore, the creeping distance between the piezoelectric transformer 20 and the voltage detection electrode 11 is the distance L1 from the piezoelectric transformer 20 to the peripheral end 37 of the printed wiring board 30, the thickness of the printed wiring board 30, and the voltage detection electrode 11 to the printed wiring board. Since it is the sum of the distance L2 to 30 peripheral ends 37, it is sufficiently long. Therefore, according to the drive circuit 10 of the present embodiment, the creeping distance between the piezoelectric transformer 20 and the voltage detection electrode 11 can be sufficiently increased even when the piezoelectric transformer 20 and the voltage detection electrode 11 are brought close to each other. The insulation between the piezoelectric transformer 20 and the voltage detection electrode 11 can be improved without impairing the sensitivity.

  FIG. 3 is a circuit diagram showing the configuration of the input side of the piezoelectric transformer in the power supply device of FIG. FIG. 5 is a waveform diagram showing waveforms in each part of the power supply device of FIGS. 1 and 3. 6 is a waveform diagram showing the operation of the power supply device of FIG. 1, FIG. 6 [1] is a case where the output current (output voltage) is lowered, and FIG. 6 [2] is a case where the output current (output voltage) is increased. This is the case. Hereinafter, description will be made based on FIGS. 1, 3, 5, and 6.

  FIG. 3 shows specific examples of the frequency control unit 60, the duty ratio control unit 70, the voltage control unit 40, and the current control unit 50. The duty ratio controller 70 compares the DC voltage Va (waveform A in FIG. 5) with the triangular wave voltage Vb (waveform B in FIG. 5), and based on the time when Va <Vb and the time when Va> Vb, The frequency F and the duty ratio Du (waveform C in FIG. 5) used when applying Vd (waveform D in FIG. 5) are determined. The frequency control unit 60 generates a triangular wave voltage Vb. The voltage control unit 40 changes the frequency of the triangular wave voltage Vb based on the output voltage signal Vv output from the voltage detection unit 14. The current control unit 50 changes the voltage value of the DC voltage Va based on the difference between the output current signal Vi output from the current detection unit 13 and the reference voltage Vr output from the reference voltage unit 18, and changes the triangular wave voltage Vb. Change the frequency.

  Next, the configuration and operation of each unit will be described in more detail.

  The supply voltages V1 and V2 are predetermined voltage values obtained by lowering the input voltage Vi using a Zener diode or a voltage dividing resistor (V2> V1). The frequency control unit 60 includes a comparator 61, an FET 62, a capacitor 63, resistors 64-68, and the like. The divided voltage V1− of the supply voltage V1 generated by the resistors 64 and 65 is applied to the −input terminal of the comparator 61. The charging voltage V1 + of the capacitor 63 is applied to the + input terminal of the comparator 61. The charging voltage V1 + gradually increases with a time constant determined by the resistor 66 and the capacitor 63. When the charging voltage V1 + exceeds the divided voltage V1-, the output voltage of the comparator 61 becomes H level, whereby the FET 62 is turned on and the charging voltage V1 + is discharged. By repeating this operation, a continuous triangular wave voltage Vb is generated. The time constant determined by the resistor 66 and the capacitor 63 is set to the frequency F when the output current Io is reduced to the minimum value, that is, the highest frequency F.

  The duty ratio control unit 70 includes a comparator 71, a diode 72, a capacitor 73, resistors 74 to 77, and the like. The capacitor 73 is for noise countermeasures. A DC voltage Va, which is a divided voltage of the supply voltage V <b> 1 generated by the resistors 75 and 76, is applied to the − input terminal of the comparator 71. The triangular wave voltage Vb output from the frequency control unit 60 is applied to the + input terminal of the comparator 71. The comparator 71 outputs an L level voltage if Va> Vb, and outputs an H level voltage if Va <Vb. The L level output time is the off time, and the H level output time is the on time. Accordingly, the H level output time / (L level output time + H level output time) is the duty ratio Du, and 1 / (L level output time + H level output time) is the frequency F.

  The DC voltage Va is set higher than the voltage value at which the set value of the output current Io is minimized or the divided voltage V1− determined by the resistors 64 and 65. If the DC voltage Va is the same as the divided voltage V1-, the output of the comparator 71 becomes L level when the duty ratio Du is 0%. When the DC voltage Va is lowered in this state, the duty ratio Du increases, and when the DC voltage Va is lowered to ½ of the initial value, the duty ratio Du becomes 50%.

  The current control unit 50 includes a comparator 51, diodes 52 and 53, capacitors 54 to 56, resistors 57 to 59, and the like. The capacitor 54 is for phase compensation between the input and output of the comparator 51. The diode 52 and the resistor 58 are for charging the capacitor 63, and the diode 53 and the resistor 59 are for adjusting the DC voltage Va. The resistor 57 is for current limiting, and the capacitors 55 and 56 are for noise countermeasures. The reference voltage Vr is applied to the + input terminal of the comparator 51, and the output current signal Vi output from the current detector 13 is applied to the − input terminal of the comparator 51. The comparator 51 outputs an L level voltage if Vi <Vr, and outputs an H level voltage if Vi> Vr. However, the output current signal Vi in the positive voltage power source 101 is set so as to decrease as the output current Io increases and to increase as the output current Io decreases.

  When the H level voltage is output from the comparator 51, a current flows through the resistor 58 → the diode 52 → the capacitor 63, thereby increasing the charging current of the capacitor 63. As a result, since the slope of the triangular wave voltage Vb becomes steep, the frequency F of the triangular wave voltage Vb increases (FIG. 6 [2] → [1]). Further, when the H level voltage is output from the comparator 51, the current flowing through the resistor 76 increases through the diode 53 and the resistor 59, so that the DC voltage Va increases, so the duty ratio Du decreases ( FIG. 6 [2] → [1]). At this time, when the L level voltage is output from the comparator 51, the reverse bias voltage is applied to the diodes 52 and 53 and the current does not flow, so the frequency F of the triangular wave voltage Vb decreases and the duty ratio Du increases ( FIG. 6 [1] → [2]).

  The resistance value of the resistor 58 covers the maximum value and the maximum load of the output current Io in a range where the charging time constant of the capacitor 63 does not fall below the resonance frequency when the output of the comparator 51 becomes an L level voltage. Set the frequency so that it is possible. The resistor 59 changes the divided voltage of the resistor 75 and the resistor 76, that is, the DC voltage Va.

  Further, the output current signal Vi in the negative voltage power source 102 is set so as to increase as the output current Io decreases and decrease as the output current Io increases. Therefore, contrary to the comparator 51 in the positive voltage power supply 101, the output current signal Vi is applied to the + input terminal and the reference voltage Vr is applied to the − input terminal.

  The voltage control unit 40 includes a comparator 41, a diode 42, a capacitor 43, resistors 44 and 45, and the like. The capacitor 43 is for phase compensation between the input and output of the comparator 41. The diode 42 and the resistor 44 are for charging the capacitor 63. The resistor 45 is for current limiting. The output voltage signal Vv output from the voltage detector 14 is applied to the + input terminal of the comparator 41, and the supply voltage V <b> 1 is applied to the − input terminal of the comparator 41. The comparator 41 outputs an L level voltage if Vv <V1, and outputs an H level voltage if Vv> V1. However, the output voltage signal Vv is set so as to increase as the output voltage Vo increases and decrease as the output voltage Vo decreases.

  When the H level voltage is output from the comparator 41, a current flows through the resistor 44, the diode 42, and the capacitor 63, whereby the charging current of the capacitor 63 increases. As a result, since the slope of the triangular wave voltage Vb becomes steep, the frequency F of the triangular wave voltage Vb increases (FIG. 6 [2] → [1]). At this time, when an L level voltage is output from the comparator 51, a reverse bias voltage is applied to the diode 42 and no current flows, so the frequency F of the triangular wave voltage Vb decreases (FIG. 6 [1] → [2]). ).

  FIG. 4 is a circuit diagram showing the configuration of the output side of the piezoelectric transformer in the power supply device of FIG. Hereinafter, description will be given based on FIG. 1 and FIGS. 4 to 6.

  In FIG. 4, specific examples of the high voltage rectification units 191 and 192, the voltage detection unit 14, and the current detection unit 13 are shown.

  The high-voltage rectifying unit 191 includes diodes 193 and 194, capacitors 195 and 196, a resistor 197, and the like. The high-voltage rectifying unit 191 rectifies the AC voltage (waveform E in FIG. 5) output from the piezoelectric transformer 20 into a positive DC voltage. The output voltage Vo is applied to the load 90. At this time, the current flowing through the load 90 is a positive output current Io +. The high voltage rectifying unit 192 has the same configuration as the high voltage rectifying unit 191 except that the directions of the diodes 193 ′ and 194 ′ are opposite to each other, and the AC voltage output from the piezoelectric transformer 20 (waveform E in FIG. 5) is negative. The output voltage is rectified to a negative output voltage Vo and applied to the load 90. At this time, the current flowing through the load 90 is a negative output current Io−.

  The voltage detection unit 14 includes a diode 141, a capacitor 142, and resistors 143 to 145. The electrostatic induction voltage Vs generated from the piezoelectric transformer 20 is detected by the voltage detection electrode 11 provided in the vicinity of the piezoelectric transformer 20 and is input to the voltage detection unit 14. The voltage detection unit 14 converts the electrostatic induction voltage Vs formed of an AC voltage into a DC voltage, and outputs this to the voltage control unit 40 as an output voltage signal Vv.

  The current detection unit 13 includes diodes 131 and 132 and resistors 133 to 134. The positive output current Io + passes through the diode 131 and the resistor 133 and becomes an output current signal Vi having a lower voltage value as its absolute value increases. The negative output current Io− passes through the diode 132 and the resistor 134 and becomes an output current signal Vi having a higher voltage value as its absolute value increases. The current detection unit 13 outputs an output current signal Vi corresponding to the output currents Io + and Io− to the current control unit 50.

  Next, the overall operation of the power supply apparatus 10 will be described with reference to FIGS.

  The power supply apparatus 10 of this embodiment includes an FV conversion unit 17 and a reference voltage unit 18 that set an arbitrary output current Io. The FV conversion unit 17 receives the control signal PWM output from another device. The reference voltage unit 18 outputs a reference signal Vr having a voltage value (for example, 0 to 5 V) corresponding to the duty ratio (for example, 0 to 100%). The reference signal Vr is output to the + input terminal of the comparator 51 as a set value corresponding to the output current Io.

  On the other hand, when the selection signal S is input, the output switching unit 12 supplies the DC input voltage Vin to either the positive voltage power supply 101 or the negative voltage power supply 102. Supply voltages V1 and V2 are generated from the input voltage Vin, the supply voltage V1 is further divided to generate a DC voltage Va, and a triangular wave voltage Vb is generated by the frequency control unit 60 (waveforms A and B in FIG. 5). ). Then, the comparator 71 compares the DC voltage Va and the triangular wave voltage Vb, and outputs an H level voltage or an L level voltage (waveform C in FIG. 5). The FET 161 is turned on / off by the frequency F and the duty ratio Du of the waveform C, whereby the drive voltage Vd (waveform D in FIG. 5) is applied to the piezoelectric transformer 20. Then, the piezoelectric transformer 20 transforms the drive voltage Vd and outputs an AC voltage (waveform E in FIG. 4). This AC voltage is rectified to become a DC output voltage Vo and supplied to the load 90. The output voltage Vo is detected by the voltage detector 14 and output to the + input terminal of the comparator 41 as the output voltage signal Vv. A supply voltage V1 that is a voltage value corresponding to the upper limit value of the output voltage Vo is applied to the negative input terminal of the comparator 41. At this time, the output current Io flowing through the load 90 is detected by the current detector 13 and output to the negative input terminal of the comparator 51 as the output current signal Vi. A reference voltage Vr corresponding to the set value of the output current Io is applied to the + input terminal of the comparator 51. Here, only the current controller 50 of the positive voltage power supply 101 will be described.

  Here, it is assumed that the output current Io has decreased from the set value due to a load change or the like. Then, since the output current signal Vi increases as the output current Io decreases, the comparator 51 outputs an L level voltage when Vr <Vi. As a result, the gradient of the triangular wave voltage Vb becomes gentle and the DC voltage Va decreases, whereby the frequency F decreases and the duty ratio Du increases (FIG. 6 [1] → [2]). As a result, the output voltage Vo increases and the output current Io also increases.

  On the contrary, it is assumed that the output current Io has increased from the set value due to load fluctuation or the like. Then, the comparator 51 outputs an H level voltage when Vr> Vi. As a result, the slope of the triangular wave voltage Vb becomes steep and the DC voltage Va rises, whereby the frequency F rises and the duty ratio Du decreases (FIG. 6 [2] → [1]). As a result, the output voltage Vo decreases and the output current Io also decreases.

  Further, if the output voltage Vo rises and exceeds the upper limit value, the output voltage signal Vv rises as the output voltage Vo rises. Therefore, the comparator 41 outputs an H level voltage when V1 <Vv. . As a result, since the slope of the triangular wave voltage Vb becomes steep, the frequency F decreases, so the output voltage Vo decreases.

  Note that the output change when the frequency F is changed and the output change when the duty ratio Du is changed are much steeper when the frequency F is changed than when the duty ratio Du is changed. Therefore, the output is balanced at a certain point even if the frequency F and the duty Du are changed simultaneously.

  FIG. 7 is a graph showing an example of the relationship between the frequency F and the duty ratio Du and the output voltage Vo in the power supply device 10.

  In this graph, one output voltage Vo on the horizontal axis corresponds to one frequency F and one duty ratio Du on the vertical axis. For example, when the reference voltage Vr is 0.15 V, as shown in the figure, the frequency F is 165.00 kHz (F1) and the duty ratio Du is 51% (D1), and the maximum output voltage 3300 V (that is, the maximum output current). Is obtained. If the reference voltage Vr is 2.38 V, the frequency F is 188.23 kHz (F2) and the duty ratio Du is 21% (D2), as shown in the figure, and the minimum output voltage 6 V (that is, the minimum output current). Is obtained.

  FIG. 8 is a graph showing an example of the relationship between the frequency F and the output voltage Vo in the power supply device 10.

  The frequency F of the drive voltage Vd is always higher than the resonance frequency of the piezoelectric transformer 20. In the figure, the case of scanning from the high frequency side is indicated by a solid line, and the case of scanning from the low frequency side is indicated by a two-dot chain line. Specifically, the frequency F of the drive voltage Vd is always higher than the frequency (164 kHz) at which the maximum value of the output voltage Vo (that is, the maximum output current) is obtained when scanning from the low frequency side.

  Needless to say, the present invention is not limited to the above embodiment. For example, instead of controlling the frequency F and the duty ratio Du of the drive voltage Vd, the drive voltage Vd may be controlled by controlling the input voltage Vin.

It is a block diagram which shows one Embodiment of the power supply device which concerns on this invention. FIG. 2 shows an example of a voltage detection electrode in the power supply device of FIG. 1, FIG. 2 [1] is a plan view of the voltage detection electrode, and FIG. 2 [2] is a cross-sectional view taken along line II in FIG. (Illustrated above). FIG. 2 is a circuit diagram illustrating a configuration of an input side of a piezoelectric transformer in the power supply device of FIG. 1. FIG. 2 is a circuit diagram illustrating a configuration of an output side of a piezoelectric transformer in the power supply device of FIG. 1. It is a wave form diagram which shows the waveform in each part of the power supply device of FIG.1 and FIG.3. FIGS. 6A and 6B are waveform diagrams showing the operation of the power supply device of FIG. 1. FIG. 6 [1] shows a case where the output current (output voltage) is lowered, and FIG. is there. 2 is a graph showing an example of the relationship between the frequency and duty ratio of a drive voltage and the output voltage in the power supply device of FIG. 1. 2 is a graph showing an example of a relationship between a drive voltage frequency and an output voltage in the power supply device of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Power supply device 101 Positive voltage power supply 102 Negative voltage power supply 11 Voltage detection electrode (output detection part, voltage detection means)
12 Output switching unit 13 Current detection unit (output detection unit)
133,134 Resistor (output detection unit, current detection means)
14 Voltage detector (output detector)
DESCRIPTION OF SYMBOLS 15 Drive voltage control part 16 Drive part 20 Piezoelectric transformer 30 Printed wiring board 40 Voltage control part 50 Current control part 60 Frequency control part 70 Duty ratio control part 90 Load

Claims (8)

A piezoelectric transformer that transforms the applied drive voltage and supplies it to the load as an output voltage, an output detection unit having voltage detection means for detecting the output voltage of the piezoelectric transformer, and an output voltage detected by the output detection unit A power supply device using a piezoelectric transformer, comprising: a driving voltage control unit that controls the driving voltage based on the driving voltage control unit; and a driving unit that applies the driving voltage controlled by the driving voltage control unit to the piezoelectric transformer.
The voltage detection means is a voltage detection electrode that detects an electrostatic induction voltage due to an output voltage of the piezoelectric transformer.
A power supply device using a piezoelectric transformer. The voltage detection electrode is formed on the printed wiring board on which the piezoelectric transformer is mounted together with the wiring of the printed wiring board.
A power supply device using the piezoelectric transformer according to claim 1. The drive voltage control unit has a function of controlling the drive voltage only by an electrostatic induction voltage detected by the voltage detection electrode.
A power supply device using the piezoelectric transformer according to claim 1. The output detection unit further includes current detection means for detecting an output current of the piezoelectric transformer,
The drive voltage control unit adjusts the drive voltage so that the output voltage detected by the output detection unit does not exceed a set value and the output current detected by the output detection unit is equal to the set value. Have the ability to control,
A power supply device using the piezoelectric transformer according to claim 1. The drive voltage control unit has a function of controlling the drive voltage by controlling at least one of a frequency and a duty ratio of the drive voltage;
A power supply device using the piezoelectric transformer according to claim 4. When the frequency and the duty ratio at which the output current is maximum are F1 and D1, respectively, and the frequency and the duty ratio at which the output current is minimum are F2 and D2, respectively.
If the detected output current is smaller than the set value, the drive voltage control unit brings the frequency and the duty ratio closer to F1 and D1, respectively. Conversely, the detected output current is less than the set value. If larger, the frequency and the duty ratio have a function of approaching F2 and D2, respectively.
A power supply device using the piezoelectric transformer according to claim 5. The drive voltage controller is
A frequency control unit for generating a variable frequency triangular wave voltage Vb;
A duty ratio control unit that compares the triangular wave voltage Vb generated by the frequency control unit with a DC voltage Va having a variable voltage value and determines the duty ratio based on a time in which Va <Vb and a time in which Va>Vb; ,
A voltage control unit that changes at least one of the voltage value of the DC voltage Va and the frequency of the triangular wave voltage Vb based on the output voltage detected by the output detection unit;
A current control unit that changes at least one of the voltage value of the DC voltage Va and the frequency of the triangular wave voltage Vb based on the output current detected by the output detection unit;
A power supply device using the piezoelectric transformer according to claim 5 or 6. Used as a DC bias power source for electrophotographic devices,
A power supply device using the piezoelectric transformer according to claim 1.

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