JP2007043804A - Piezoelectric transformer output detector and power supply using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric transformer output detector for accurately detecting an output voltage and an output current. <P>SOLUTION: The piezoelectric transformer output detector 10 is attached to a rectification section 30 for converting an AC voltage generated from a piezoelectric transformer 20 into a DC voltage and outputting it from output terminals 31, 32, and includes voltage detecting resistors 11, 12 for detecting the output voltage Vo as a voltage applied to a load 90 connected between the output terminal 31 and a ground terminal 91, a current detecting resistor 13 for detecting the output current Io as a current flowing in the load 90, and an operational amplifier 14 having an inverting input terminal 141, a non-inverting input terminal 142 and an output terminal 143. The non-inverting input terminal 142 is connected to the ground terminal 91. The inverting input terminal 141 is connected to the output terminal 32. The voltage detecting resistors 11, 12 are connected between the output terminals 31, 32. The current detecting resistor 13 is connected between the output terminal 143 and the inverting input terminal 141. <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 piezoelectric transformer output detection device and a power supply device using the same.

  In a high voltage generator using a piezoelectric transformer, constant voltage control for controlling the output voltage to be constant is common. However, there are cases where constant current control for controlling the output current to be constant is performed in a copying machine or printer using electrophotographic technology, or some air purifiers. In that case, it was not necessary to shift from constant current control to constant voltage control, and it was sufficient if the no-load voltage could be suppressed.

  In other words, in a DC bias power source using a piezoelectric transformer, when the output current is controlled at a constant current, the output voltage is maximized when there is no load because the constant current is maintained by increasing the output voltage when the load resistance increases. It becomes. If this is left as it is, the piezoelectric transformer may be damaged by applying excessive mechanical vibration to the piezoelectric transformer. Therefore, a resistor is inserted into the output circuit to detect the output voltage, and control is performed so that the output voltage does not exceed a certain level (for example, Patent Document 1).

Japanese Patent No. 3396017

  However, recently, a load requiring constant voltage characteristics and constant current characteristics has been used. For such a load, the specifications cannot be satisfied only by the conventional constant voltage control or the constant current control. Here, when the conventional technique is used to realize constant voltage and constant current control, a current (hereinafter referred to as “voltage detection current”) that flows through a resistor that detects an output voltage (hereinafter referred to as “voltage detection resistor”). And a current (hereinafter referred to as “current detection current”) flowing through a resistor for detecting an output current (hereinafter referred to as “current detection resistor”) flows in a mixed manner. For example, a current detection current flows through the voltage detection resistor, or conversely, a voltage detection current flows through the current detection resistor. As a result, there arises a problem that the detection accuracy of the output voltage and the output current is lowered.

  Accordingly, an object of the present invention is to provide a piezoelectric transformer output detection device capable of accurately detecting an output voltage and an output current and a power supply device using the same.

  The piezoelectric transformer output detection device according to the present invention is attached to a rectifying unit that converts an AC voltage generated by the piezoelectric transformer into a DC voltage and outputs the DC voltage from the first and second output terminals. The piezoelectric transformer output detection device according to the present invention includes a voltage detection resistor that detects an output voltage, which is a voltage applied to a load connected between the first output terminal and the ground terminal, and flows through the load. A current detection resistor for detecting an output current as a current and an operational amplifier having an inverting input terminal, a non-inverting input terminal, and an output terminal are provided. In addition, the non-inverting input terminal is connected to the ground terminal, the inverting input terminal is connected to the second output terminal, a voltage detection resistor is connected between the first output terminal and the second output terminal, and the output A current detection resistor is connected between the terminal and the inverting input terminal.

  For example, assume that a high voltage is output from the first output end and a low voltage is output from the second output end. At this time, the current flowing from the first output terminal to the second output terminal is the first output terminal → load → grounding terminal → inside of operational amplifier → output terminal → current detection resistor → second output terminal. The first loop is divided into a second loop including a first output terminal → a voltage detection resistor → a second output terminal. At this time, since the current output from the piezoelectric transformer is very small, the current flows from the ground end to the inside of the operational amplifier to the output terminal via, for example, the ground end in the power supply circuit that supplies a voltage to the operational amplifier.

  The current flowing through the first loop is the current flowing through the load, that is, the output current. On the other hand, the voltage drop at the voltage detection resistor due to the current flowing in the second loop (the first output terminal → the voltage detection resistor → the voltage drop at the second output terminal) is the voltage applied to the load, that is, the output It is equal to the voltage (voltage drop at the first output terminal → load → ground terminal). Because the second output terminal is connected to the inverting input terminal and the non-inverting input terminal is connected to the ground terminal, the inverting input terminal becomes the same potential as the non-inverting input terminal by the virtual ground, that is, the ground potential. is there.

  At this time, the currents flowing through the first and second loops are independent of each other. That is, current detection current does not flow through the voltage detection resistor, and conversely, voltage detection current does not flow through the current detection resistor, so that the detection accuracy of the output voltage and output current is improved. The same applies when a low voltage is output from the first output end and a high voltage is output from the second output end.

  According to a second aspect of the present invention, in the piezoelectric transformer output detection device according to the first aspect, the output terminal is connected to the ground terminal via the internal impedance of the operational amplifier.

  At this time, since the current output from the piezoelectric transformer is very small, it flows through the internal impedance of the operational amplifier to the ground terminal → the operational amplifier internal → the output terminal or vice versa.

  The piezoelectric transformer output detection device according to claim 3 is the piezoelectric transformer output detection device according to claim 1 or 2, wherein the non-inverting input terminal is fixed to a constant potential instead of being connected to the ground terminal. That's it.

  Since the non-inverting input terminal is grounded, the voltage drop of the current detection resistor or the voltage detection resistor with respect to the inverting input terminal may be negative. In this case, by fixing the non-inverting input terminal to a positive constant potential, the voltage drop of the current detection resistor or the voltage detection resistor can be made positive, so that control is facilitated.

  The piezoelectric transformer output detection device according to claim 4 is the piezoelectric transformer output detection device according to any one of claims 1 to 3, wherein the rectifying units are arranged in opposite directions to the output end of the piezoelectric transformer. And a smoothing capacitor connected between the other end of the first rectifier diode and the other end of the second rectifier diode, and a first output. One end is connected to the other end of the first rectifier diode, and the second output end is connected to the other end of the second rectifier diode.

  In this case, the rectifier unit forms a double voltage rectifier circuit together with the internal capacitance of the piezoelectric transformer. Here, it is assumed that the directions of the first and second rectifier diodes are determined so that a high voltage is output from the first output terminal and a low voltage is output from the second output terminal. At this time, the current flowing through the piezoelectric transformer output detection device is as follows: the positive electrode of the smoothing capacitor → the first output terminal → the load → the ground terminal → the inside of the operational amplifier → the output terminal → the current detection resistor → the second output terminal → the smoothing capacitor. First loop consisting of negative electrode, positive electrode of smoothing capacitor → first output terminal → voltage detection resistor → second output terminal → second loop consisting of negative electrode of smoothing capacitor, and input terminal of piezoelectric transformer → grounding End → Operational amplifier inside → Output terminal → Current detection resistor → Second output terminal → Second rectifier diode → Piezoelectric transformer output terminal → Piezoelectric transformer output terminal → First rectifier diode -> Smoothing capacitor-> Current detection resistor-> Output terminal-> Inside of operational amplifier-> Ground end-> Fourth loop consisting of piezoelectric transformer input end

  The third loop is a current loop that charges the internal capacitance of the piezoelectric transformer with the negative half wave of the AC voltage generated in the piezoelectric transformer. The fourth loop is a current loop that charges the smoothing capacitor together with the charging voltage of the internal capacitance of the piezoelectric transformer by the positive half wave of the AC voltage generated by the piezoelectric transformer. The first and second loops are current loops that supply a load by discharging a smoothing capacitor. The first and second loops are as described above. The current flowing in the current detection resistor by the third loop and the current flowing in the current detection resistor by the fourth loop are opposite in direction and equal in magnitude. For example, a capacitor is connected in parallel to the current detection resistor. Is offset by Therefore, a voltage drop due to only the current due to the first loop, that is, the output current, occurs in the current detection resistor.

  The piezoelectric transformer output detection device according to claim 5 is the piezoelectric transformer output detection device according to claim 4, wherein one end of the first rectifier diode is an anode and the other end is a cathode, and the second rectifier diode is one end. It is a cathode and the other end is an anode. In this case, the rectifier outputs a positive voltage and current.

  The piezoelectric transformer output detection device according to claim 6 is the piezoelectric transformer output detection device according to claim 4, wherein one end of the first rectifier diode is a cathode and the other end is an anode, and one end of the second rectifier diode is an end. It is an anode and the other end is a cathode. In this case, the rectifier outputs a negative voltage and current.

  A power supply device according to the present invention includes a piezoelectric transformer output detection device according to the present invention, a piezoelectric transformer that transforms an applied drive voltage to generate a high-voltage AC voltage, and an AC voltage generated by the piezoelectric transformer is converted to a DC voltage. A rectifier that converts and supplies the output voltage to the load, a drive voltage controller that controls the drive voltage based on the output voltage and output current detected by the piezoelectric transformer output detector, and a drive controlled by the drive voltage controller And a drive unit that applies a voltage to the piezoelectric transformer.

  In other words, in the present invention, constant voltage control and constant current control are performed by using the characteristics of the operational amplifier and feeding the current flowing through the voltage detection resistor back to the rectifying unit by virtual grounding and not passing through the current detection resistor. It can be performed with high accuracy.

  According to the piezoelectric transformer output detection device of the present invention, for example, when a high voltage is output from the first output end of the rectifying unit and a low voltage is output from the second output end of the rectifying unit, Output terminal-> Load-> Ground terminal-> Operational amplifier inside-> Output terminal-> Current detection resistor-> Current detection current loop consisting of second output terminal and first output terminal-> Voltage detection resistor-> Second output terminal Since the current detection current does not flow through the voltage detection resistor or the voltage detection current does not flow into the current detection resistor. The detection accuracy of the output voltage and output current can be improved. Moreover, according to this invention, there exist the following effects for every claim.

  According to the piezoelectric transformer output detection device according to claim 2, the output terminal of the operational amplifier is connected to the ground terminal via the internal impedance of the operational amplifier, so that the ground terminal is connected to the ground terminal via the internal impedance of the operational amplifier. A current detection current can be reliably passed between the output terminal of the operational amplifier.

  According to the piezoelectric transformer output detection device of the third aspect, the voltage drop of the current detection resistor or the voltage detection resistor can be made positive by fixing the non-inverting input terminal to a constant potential. It can be simplified.

  According to the piezoelectric transformer output detection device of the fourth aspect, even when the rectification unit is a double voltage rectification circuit, currents other than the output current flowing through the current detection resistor cancel each other out. The output current can be accurately detected.

  According to the power supply device according to the present invention, since the output voltage and the output current can be accurately detected by using the piezoelectric transformer output detection device according to the present invention, highly accurate constant voltage constant current control can be realized.

  FIG. 1 is a circuit diagram showing a first embodiment of a piezoelectric transformer output detection device according to the present invention. FIG. 2 is a circuit diagram showing an example of an equivalent circuit of a general operational amplifier. Hereinafter, description will be given based on these drawings.

  The piezoelectric transformer output detection device 10 according to the present embodiment is attached to a rectifying unit 30 that converts an alternating voltage generated by the piezoelectric transformer 20 into a direct current voltage and outputs it from output terminals 31 and 32. The piezoelectric transformer output detection device 10 includes voltage detection resistors 11 and 12 that detect an output voltage Vo that is a voltage applied to a load 90 connected between the output terminal 31 and the ground terminal 91, and a load 90. And an operational amplifier 14 having an inverting input terminal 141, a non-inverting input terminal 142, and an output terminal 143. The non-inverting input terminal 142 is connected to the ground terminal 91, the inverting input terminal 141 is connected to the output terminal 32, and the voltage detection resistors 11 and 12 are connected between the output terminal 31 and the output terminal 32, and the output The current detection resistor 13 is connected between the terminal 143 and the inverting input terminal 141.

  In the present embodiment, an AC component absorbing and noise absorbing capacitor 15 is connected in parallel to the current detection resistor 13, and a noise absorbing capacitor is connected between both ends of the voltage detection resistor 11 and the ground terminal 91. Capacitors 16 and 17 are connected. Further, the voltage detection resistors 11 and 12 divide the output voltage Vo. A voltage drop in the voltage detection resistor 11 is output as an output voltage signal Vv corresponding to the output voltage Vo. An output current Io flows through the current detection resistor 13 as will be described later. A voltage drop in the current detection resistor 13 is output as an output current signal Vi corresponding to the output current IVo.

  The operational amplifier 14 has an extremely large input impedance Ri, an extremely small output impedance Ro, and an extremely large open loop gain An. The output terminal 143 is connected to the ground terminal 91 via an internal impedance composed of the output impedance Ro of the operational amplifier 14 or the like.

  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 AC voltage Vo ′ corresponding to the vibration is output from the secondary side by the piezoelectric effect. The The AC voltage Vo ′ is converted into a DC positive voltage output voltage Vo by the rectifier 30 and applied to the load 90.

  The rectifier 30 includes a rectifier diode 33 having an anode connected to the secondary electrode 24 of the piezoelectric transformer 20, a rectifier diode 34 having a cathode connected to the secondary electrode 24, an anode of the rectifier diode 34, and a cathode of the rectifier diode 33. The output terminal 31 is connected to the cathode of the rectifier diode 33 via the current limiting resistor 36, and the output terminal 32 is connected to the cathode of the rectifier diode 34. Is. The rectifier 30 constitutes a double voltage rectifier circuit together with the internal capacitance (not shown) of the piezoelectric transformer 20, and outputs a positive DC high voltage output voltage Vo from the output terminal 31.

  Next, the operation of the piezoelectric transformer output detection device 10 will be described.

  The current flowing through the piezoelectric transformer output detection device 10 is as follows: positive electrode of the smoothing capacitor 35 → output terminal 31 → load 90 → grounding terminal 91 → inside of operational amplifier 14 → output terminal 143 → current detection resistor 13 → output terminal 32 → smoothing capacitor A first loop composed of 35 negative electrodes, a second loop composed of the positive electrode of the smoothing capacitor 35 → the output terminal 31 → the voltage detection resistor 12, 11 → the output terminal 32 → the negative electrode of the smoothing capacitor 35, and the piezoelectric transformer 20. A third loop composed of the primary electrode 23 → the ground terminal 91 → the inside of the operational amplifier 14 → the output terminal 143 → the current detection resistor 13 → the output terminal 32 → the rectifier diode 34 → the secondary electrode 24 of the piezoelectric transformer 20; 20 secondary electrode 24 → rectifier diode 33 → smoothing capacitor 35 → current detection resistor 13 → output terminal 143 → inside of operational amplifier 14 → connection Divided into a fourth loop consisting of primary electrodes 23 of the end 91 → the piezoelectric transformer 20.

  The current flowing through the first loop is the current flowing through the load 90, that is, the output current Io. On the other hand, the voltage drop at the voltage detection resistors 11 and 12 due to the current flowing through the second loop (the voltage drop at the output terminal 31 → the voltage detection resistors 11, 12 → the terminal terminal 32) is applied to the load 90. It is equal to the voltage, that is, the output voltage Vo (voltage drop at the output end 31 → the load 90 → the ground end 91). Because the output terminal 32 is connected to the inverting input terminal 141 and the non-inverting input terminal 142 is connected to the ground terminal 91, the inverting input terminal 141 is set to the same potential as the non-inverting input terminal 142 by the virtual ground, that is, the ground potential. Because it becomes.

  At this time, the currents flowing through the first and second loops are independent of each other. That is, since the current detection current does not flow through the voltage detection resistor 11 and the voltage detection current does not flow through the current detection resistor 13, the detection accuracy of the output voltage Vo and the output current Io is high. improves.

  The current flowing through the third loop is a current that charges the internal capacitance of the piezoelectric transformer 20 by the negative half wave of the AC voltage Vo ′ generated in the piezoelectric transformer 20. The current flowing through the fourth loop is a current that charges the smoothing capacitor 35 together with the charging voltage of the internal capacitance of the piezoelectric transformer 20 by the positive half wave of the AC voltage Vo ′ generated by the piezoelectric transformer 20. Since the current flowing in the current detection resistor 13 by the third loop and the current flowing in the current detection resistor 13 by the fourth loop are opposite in direction and equal in magnitude, they are connected in parallel to the current detection resistor 13. It is canceled out by the capacitor 15. Therefore, a voltage drop due to only the current by the first loop, that is, the output current Io occurs in the current detection resistor 13.

  Next, a supplementary explanation of the operation of the operational amplifier 14 in the path from the ground end 91 of the first loop → the inside of the operational amplifier 14 → the output terminal 143 → the current detection resistor 13 → the output end 32 will be supplemented. The operational amplifier 14 outputs a voltage (that is, an output current signal Vi) corresponding to r × Io to the output terminal 143 in order to maintain the virtual ground in the first loop, that is, to set the output terminal 32 to the ground potential. . Here, r is the resistance value of the current detection resistor 13. As a result, there are two voltage sources, the smoothing capacitor 35 and the operational amplifier 14, in the first loop. Then, due to superposition, the sum of the currents from the two voltage sources becomes the current that actually flows. However, since the voltage of the smoothing capacitor 35 is several kV, for example, and the voltage of the operational amplifier 14 is several volts, for example, the current flowing through the operational amplifier 14 can be ignored.

  FIG. 3 is a circuit diagram (partly including a block) showing the first embodiment of the power supply device according to the present invention. Hereinafter, description will be given based on this drawing.

  The power supply device 100 of the present embodiment includes a piezoelectric transformer output detection device 10, a piezoelectric transformer 20 that transforms an applied drive voltage Vd to generate a high-voltage AC voltage Vo ′, and an AC voltage Vo generated by the piezoelectric transformer 20. The rectifier 30 that converts' to a DC voltage and supplies it to the load 90 as the output voltage Vo, and the drive voltage control that controls the drive voltage Vd based on the output voltage Vo and the output current Io detected by the piezoelectric transformer output detection device 10 And a driving unit 110 that applies the driving voltage Vd controlled by the driving voltage control unit 120 to the piezoelectric transformer 20.

  Since the piezoelectric transformer output detection device 10, the piezoelectric transformer 20, and the rectifying unit 30 are as described above, detailed description thereof is omitted. The drive unit 110 includes BJTs 111 and 112, an FET 113, an inductor 114, a capacitor 115, and the like. The BJTs 111 and 112 constitute a complementary circuit and function as a buffer.

  The drive voltage control unit 120 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 variable voltage DC voltage Va, and Va <Vb. A duty ratio controller 70 that determines the duty ratio Du based on a certain time and a time Va> Vb, and a voltage controller that changes the frequency of the triangular wave voltage Vb based on the output voltage Vo detected by the piezoelectric transformer output detector 10. 40, a current control unit 50 that changes 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 piezoelectric transformer output detection device 10, and a reference signal Vr generated by the reference voltage unit 124 An on / off control unit 80 for stopping the operation of the drive unit 110 to reliably turn off the output voltage Vo when a certain level is reached. That.

  The drive voltage control unit 120 is additionally provided with a Zener diode 121, a capacitor 122, a resistor 123, a reference voltage unit 124, and the like. The Zener diode 121 and the like step down the DC input voltage Vin and generate the supply voltage V2. The reference voltage unit 124 receives the control signal PWM output from another device, and 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 corresponds to a constant current Io1 used in constant current control.

  FIG. 4 [1] is a circuit diagram illustrating a configuration example of a frequency control unit and a duty ratio control unit in the power supply device of FIG. FIG. 4 [2] is a graph showing constant voltage constant current control in the power supply device of FIG. FIG. 5 is a waveform diagram showing waveforms in each part of the power supply device of FIG. 6 is a waveform diagram showing the operation of the power supply device of FIG. 3, 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, a description will be given with reference to FIGS.

  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 piezoelectric transformer output detection device 10. 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 piezoelectric transformer output detection device 10 and the reference signal Vr output from the reference voltage unit 124, and also changes the triangular wave voltage. Change the frequency of Vb.

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

  The supply voltage V1 is a predetermined voltage value obtained by lowering the supply voltage V2 using a Zener diode or a voltage dividing resistor (not shown). The frequency control unit 60 includes a comparator 61, an FET 62, a capacitor 63, resistors 64-68, a diode 72, a resistor 74, 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. In the present embodiment, the output current Io decreases as the frequency F is increased. The diode 72 and the resistor 74 are for temperature correction. Usually, a variable resistor is used as the resistor 74, and the resistance value is set so that the frequency F does not exceed the resonance point.

  The duty ratio control unit 70 includes a comparator 71, a capacitor 73, resistors 75 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 and 55, resistors 56 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 capacitor 55 is for preventing abnormal oscillation. The reference signal Vr is applied to the − input terminal of the comparator 51, and the output current signal Vi output from the piezoelectric transformer detection device 10 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 is set so as to increase as the output current Io increases and decrease 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, an amplifier may be used instead of the comparator 51. In this case, a voltage corresponding to the output current signal Vi is output to the frequency control unit 60 and the duty ratio control unit 70.

  The on / off control unit 80 includes a comparator 81, resistors 82 and 83, and the like. The supply voltage V <b> 3 is applied to the negative input terminal of the comparator 81. The supply voltage V3 is a value obtained by dividing the supply voltage V2 by the resistors 82 and 83, and the duty ratio of the control signal PWM corresponds to, for example, 5%. A reference signal Vr is applied to the + input terminal of the comparator 81. The output terminal of the comparator 81 is connected to the bases of the BJTs 111 and 112. The comparator 81 outputs an L level voltage if Vr <V3, and outputs an H level voltage if Vr> V3.

  The voltage control unit 40 includes a comparator 41, a diode 42, capacitors 43 and 44, resistors 45 to 47, 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 45 are for charging the capacitor 63. Resistors 46 and 47 are for current limiting. The output voltage signal Vv output from the piezoelectric transformer detection device 10 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 45, 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]). ).

  Next, the overall operation of the power supply apparatus 100 will be described with reference to FIGS.

  First, the reference signal Vr is output to the + input terminal of the comparator 51 as the set value of the output current Io, that is, the constant current Io1. On the other hand, supply voltages V1 and V2 are generated from the input voltage Vin, and 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 (waveform A in FIG. 5). , B). 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 piezoelectric transformer detection device 10 and output to the + input terminal of the comparator 41 as the output voltage signal Vv. The supply voltage V1 corresponding to the constant voltage Vo1 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 detection unit 13 and output to the positive input terminals of the comparators 51 and 81 as the output current signal Vi. The reference signal Vr corresponding to the constant current Io1 is applied to the negative input terminal of the comparator 51. A supply voltage V3 corresponding to the no-load current Io2 is applied to the negative input terminal of the comparator 81.

  Here, it is assumed that the output current Io rises due to a load change or the like and exceeds a certain current Io1. Then, since the output current signal Vi increases as the output current Io increases, 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 increases, so that the frequency F increases and the duty ratio Du decreases (FIG. 6 [2] → [1]). As a result, the output current Io decreases.

  On the contrary, it is assumed that the output current Io decreases and falls below the constant current Io1. Then, 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 current Io increases.

  Here, it is assumed that the output voltage Vo rises due to a load change or the like and exceeds a certain voltage Vo1. Then, as the output voltage Vo increases, the output voltage signal Vv also increases. 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 increases, so that the output voltage Vo decreases (FIG. 6 [2] → [1]).

  On the contrary, it is assumed that the output voltage Vo decreases and falls below a certain voltage Vo1. Then, as the output voltage Vo decreases, the output voltage signal Vv also decreases, so that the comparator 41 outputs an L level voltage when V1> Vv. As a result, since the slope of the triangular wave voltage Vb becomes gentle, the frequency F decreases, and the output voltage Vo increases (FIG. 6 [1] → [2]).

  Further, as a characteristic of the piezoelectric transformer 20, even if the frequency F is increased considerably, the output does not become zero because the next resonance point approaches. Therefore, if the duty ratio of the control signal PWM is greater than 5%, an H level voltage is output from the comparator 81 and the operation of the drive unit 110 is maintained. However, if the duty ratio of the control signal PWM is smaller than 5%, an L level voltage is output from the comparator 81, and the operation of the drive unit 110 is forcibly stopped.

  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.

  With the above operation, constant voltage and constant current control as shown in FIG. 4 [2] can be realized. In addition, according to the power supply device 100, since the output voltage Vo and the output current Vi can be accurately detected by using the piezoelectric transformer output detection device 10, high-precision constant voltage and constant current control can be realized.

  FIG. 7 is a circuit diagram showing a second embodiment of the piezoelectric transformer output detection device according to the present invention. Hereinafter, description will be given based on these drawings. However, the same parts as those in FIG.

  The rectifying unit 30 ′ in the present embodiment is different from the first embodiment in that the directions of the rectifying diodes 33 ′ and 34 ′ are reversed. As a result, a negative DC high voltage output voltage Vo is output from the output terminal 31. Output. The piezoelectric transformer output detection device 10 ′ in this embodiment has a constant voltage power supply 18, and the non-inverting input terminal 142 has a constant potential compared to the first embodiment in which the non-inverting input terminal 142 is connected to the ground terminal 91. The difference is that it is fixed at Vx. The constant voltage power source 18 can be constituted by, for example, a resistor that divides the supply voltages V1, V2, and the like.

  Since the negative output voltage Vo is output from the output terminal 31, the output voltage signal Vv and the output current signal Vi decrease as the output voltage Vo and the output current Ii increase. That is, when the non-inverting input terminal 12 is grounded, the output voltage signal Vv and the output current signal Vi are always negative. Therefore, by fixing the non-inverting input terminal 142 to the positive constant potential Vx, the output voltage signal Vv and the output current signal Vi can always be made positive, so that the control becomes easy.

  Note that a power supply device using the piezoelectric transformer output detection device 10 ′ and the rectifying unit 30 ′ can be configured according to the power supply device 100 of FIG. 3. However, in the present embodiment, contrary to the power supply apparatus 100, the output voltage signal Vv and the output current signal Vi decrease as the output voltage Vo and the output current Ii increase.

1 is a circuit diagram showing a first embodiment of a piezoelectric transformer output detection device according to the present invention. FIG. It is a circuit diagram which shows an example of the equivalent circuit of a general operational amplifier. 1 is a circuit diagram (partly including a block) showing a first embodiment of a power supply device according to the present invention. FIG. 4 [1] is a circuit diagram illustrating a configuration example of a frequency control unit and a duty ratio control unit in the power supply device of FIG. FIG. 4 [2] is a graph showing constant voltage constant current control in the power supply device of FIG. It is a wave form diagram which shows the waveform in each part of the power supply device of FIG. FIG. 6 is a waveform diagram illustrating the operation of the power supply device of FIG. 3, in which FIG. 6 [1] is a case where the output current (output voltage) is lowered, and FIG. is there. It is a circuit diagram which shows 2nd embodiment of the piezoelectric transformer output detection apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,10 'Piezoelectric transformer output detection apparatus 11 Voltage detection resistor 13 Current detection resistor 14 Operational amplifier 141 Inverting input terminal of operational amplifier 142 Non-inverting input terminal of operational amplifier 143 Output terminal of operational amplifier 20 Piezoelectric transformer 30, 30' Rectifier 31, 32 Output end of rectifier 90 Load 91 Ground end 100 Power supply 110 Drive unit 120 Drive voltage controller Vo Output voltage Io Output current

Claims (7)

A piezoelectric transformer output detection device attached to a rectifying unit that converts an alternating voltage generated by a piezoelectric transformer into a direct current voltage and outputs the direct voltage from the first and second output ends,
A voltage detection resistor for detecting an output voltage which is a voltage applied to a load connected between the first output terminal and the ground terminal; and a current detection resistor for detecting an output current which is a current flowing through the load And an operational amplifier having an inverting input terminal, a non-inverting input terminal and an output terminal,
The non-inverting input terminal is connected to the ground terminal, the inverting input terminal is connected to the second output terminal, and the voltage detection resistor is between the first output terminal and the second output terminal. And the current detection resistor is connected between the output terminal and the inverting input terminal,
A piezoelectric transformer output detection device. The output terminal is connected to the ground terminal via an internal impedance of the operational amplifier.
The piezoelectric transformer output detection device according to claim 1. The non-inverting input terminal is fixed to a constant potential instead of being connected to the ground terminal.
The piezoelectric transformer output detection device according to claim 1 or 2. The rectifier unit includes first and second rectifier diodes connected at opposite ends to the output end of the piezoelectric transformer, the other end of the first rectifier diode, and the second rectifier diode. A smoothing capacitor connected between the other end of the rectifier diode, the first output end connected to the other end of the first rectifier diode, and the second output end connected to the second rectifier. Connected to the other end of the diode,
The piezoelectric transformer output detection device according to claim 1, wherein the piezoelectric transformer output detection device is a piezoelectric transformer output detection device. The first rectifier diode has the one end as an anode and the other end as a cathode,
The second rectifier diode has the one end as a cathode and the other end as an anode.
The piezoelectric transformer output detection device according to claim 4. The first rectifier diode has the one end as a cathode and the other end as an anode,
The second rectifier diode has the one end as an anode and the other end as a cathode.
The piezoelectric transformer output detection device according to claim 4.
The piezoelectric transformer output detection device according to any one of claims 1 to 6, the piezoelectric transformer that transforms an applied drive voltage to generate a high-voltage AC voltage, and an AC voltage generated by the piezoelectric transformer. The rectifying unit that converts the DC voltage to supply the load as the output voltage, the drive voltage control unit that controls the drive voltage based on the output voltage and the output current detected by the piezoelectric transformer output detection device, A drive unit that applies the drive voltage controlled by the drive voltage control unit to the piezoelectric transformer;
A power supply device comprising:

Images