JP2003086858A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer that can boost a voltage supplied to its input side at a high boosting ratio by transmitting the voltage to its output side by using the transversal slipping vibration of a piezoelectric material and can be made to perform self-excitation. SOLUTION: The piezoelectric transformer has impedance (15) for detection which is connected to an input electrode (18) and detects the feedback signal corresponding to the displacement of an input voltage from the connection with the electrode (18), and a driving circuit (13) which displaces the input voltage in accordance with the feedback signal obtained from the connection between the impedance (15) and electrode (18). The transformer is made to perform self-excitation while keeping the isolation between the input side and output side by causing feedback by means of a feedback signal from the input electrode (18) side.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer, and more particularly to a piezoelectric transformer which transmits a voltage supplied to an input side to an output side by using width-slip vibration of a piezoelectric material. The present invention relates to a step-up piezoelectric transformer. Conventionally, the step-up or step-down of alternating current is
It is made by an electromagnetic transformer. An electromagnetic transformer generally has a primary winding and a secondary winding, which are electromagnetically coupled by a magnetic core. In such a configuration, it is generally inevitable that the transformer occupies a considerable space. On the other hand, especially in the field of information processing devices, for example, CR
In many cases, a small transformer is required, such as a T display, an electrostatic printer, or a DC converter. Also, in some applications, the transformer needs to be small and capable of generating voltages as high as thousands of volts. There are also applications where a large output current is required, such as an output transformer. [0003] In a transformer using piezoelectric crystals or ceramics, there has been proposed a piezoelectric transformer that generates width-swing vibration in a piezoelectric substrate, performs resonance, and boosts the voltage. FIG. 20 shows a configuration diagram of an example of a piezoelectric transformer. The piezoelectric transformer 90 proposed above has a substantially rectangular lithium niobate (LiNbO3) having a length L in the longitudinal direction or Y 'direction and a width W in the lateral direction or Z' direction.
And a piezoelectric substrate made of a crystal plate of On the upper main surface of the piezoelectric substrate, a plurality of strip electrodes extending parallel to the Z 'direction orthogonal to the Y' direction are formed, and the plurality of electrodes are formed by a first electrode group E1,
It is divided into a second electrode group E2 and a third electrode group E3. Among them, the electrode group E1 includes input electrodes, and the electrode group E2 includes output electrodes. Each electrode of the electrode group E3 is not essential, but is formed between each electrode pair of the electrode group E1 or the electrode group E2, and is commonly connected and grounded. In this embodiment, the electrodes are formed only on the upper surface of the substrate, not on the lower surface. Each of the electrode groups E1 and E2 includes two electrodes E11, E12, E21 and E22, and the length L of the substrate 91 is set according to the wavelength of the transverse wave excited in the substrate. , E2 are formed corresponding to the nodes of vibration at which the stress is maximized. When an input AC voltage Vi is applied to an adjacent pair of electrodes of the electrode group E1, an electric field acting in the Y 'direction in accordance with the direction of polarization is applied to the surface of the piezoelectric substrate. When an electric field acting in a specific direction is applied to the piezoelectric substrate, width-slip vibration is excited corresponding to the large electromechanical coupling coefficient K15. As a result of the excitation of the width-slip vibration, a transverse wave propagating in the longitudinal direction Y 'of the substrate is generated, and the transverse wave causes an elastic displacement in the lateral direction of the substrate. The transverse wave propagating in the Y 'direction is reflected back and forth and resonates. The resonated vibration becomes a node where the stress is maximum below the output electrode E2, and generates an output voltage at the output electrode E2. [0011] However, the conventional piezoelectric transformer has problems that it cannot be self-excited and has poor driving efficiency. The present invention has been made in view of the above points, and has as its object to provide a piezoelectric transformer that can be self-excited. According to the present invention, an input voltage is applied to an input electrode formed on a piezoelectric substrate to cause the piezoelectric substrate to vibrate, and the piezoelectric substrate is formed on the piezoelectric substrate in response to the vibration. In a piezoelectric transformer that obtains an output voltage from the output electrode, a detection impedance that is connected to the input electrode and detects a feedback signal corresponding to a displacement of the input voltage from a connection point with the input electrode, and the detection impedance A drive circuit for displacing the input voltage in accordance with a feedback signal obtained from a connection point with the input electrode, applying feedback by a feedback signal from the input electrode side, and maintaining isolation between input and output. While self-excited. According to the present invention, the potential change on the input side of the piezoelectric transformer can be detected by the detection impedance, and the piezoelectric transformer can be self-excited. For this reason, the isolation between the input and the output is improved, and the self-excited oscillation allows the piezoelectric transformer to follow the fluctuation of the resonance frequency of the piezoelectric transformer due to the fluctuation of the temperature and to be driven with high efficiency. FIG. 1 is a schematic diagram showing a first embodiment of a piezoelectric transformer according to the present invention. The piezoelectric transformer 1 of this embodiment includes a piezoelectric substrate 2 that performs width-slip vibration, an input electrode 3 that applies a drive voltage to the piezoelectric substrate 2, and an output electrode 4 that outputs an output voltage from the piezoelectric substrate 2. The piezoelectric substrate 2 is formed of, for example, a single crystal of X-cut lithium niobate (LiNbO3), and width-slip vibration occurs in the 163 ° Y direction by applying a voltage. The size of the piezoelectric substrate 2 is set to a length L and a width W corresponding to the wavelength of the transverse wave excited in the substrate.
The thickness of the piezoelectric substrate 2 is set to 0.2 to 0.3 mm. The input electrode 3 is composed of a first input electrode 3a and a second input electrode 3b which are separated from each other and arranged in parallel with each other. The first input electrode 3a is connected to an input terminal TIN1 connected to ground, and the second input electrode 3b is connected to an input terminal TIN2 connected to a drive voltage source. The output electrode 4 has first and second output electrodes 4a and 4b connected to the output terminals TOUT1 and TOUT2, and a Z-shaped coupling electrode for coupling the first output electrode 4a and the second output electrode 4b. 4c and 4d. First output electrode 4
a is connected to the output terminal TOUT1, and the second output electrode 4b is connected to the output terminal TOUT2. Output terminals TOUT1, TOUT2
Is connected to a load, and the first and second output electrodes 4 are connected to the load.
The output voltage generated between a and 4b is applied. FIG. 2 is a diagram for explaining the operation of the first embodiment of the piezoelectric transformer according to the present invention. When an input AC voltage Vi serving as a driving voltage is applied to the input terminals TIN1 and TIN2, the input AC voltage Vi is applied to the surface of the piezoelectric substrate 2 via the first input electrode 3a and the second input electrode 3b. . As a result, an electric field acting in the Y ′ direction is applied to the surface of the piezoelectric substrate 2. When an electric field acting on the piezoelectric substrate 2 in a specific direction is applied, width-slip vibration is excited corresponding to a large electromechanical coupling coefficient. As a result of the width-shear vibration being excited in the piezoelectric substrate 2, a transverse wave propagating in the longitudinal direction Y 'of the substrate is generated,
The transverse wave propagating in the Y 'direction, in which the elastic displacement accompanying the transverse wave occurs in the lateral direction of the piezoelectric substrate 2, is reflected back and forth and resonates. Regarding the width-slip vibration, a paper by Watanabe and Shimizu, "Energy trapping of higher-order width vibration in a piezoelectric strip and its application to a filter" IEICE Transactions A, vo1. J71-A, No. 8, pp. 14
89-1498. At this time, the length L of the piezoelectric substrate 2 is set in accordance with the wavelength of the transverse wave excited in the piezoelectric substrate 2, and the pitch between the input electrode 3 and the output electrode 4 has the maximum stress. It is set corresponding to the node of vibration. As shown in FIG. 2, when the piezoelectric substrate 2 resonates, the first output electrode 4a and the coupling electrode 4c coupled thereto, the coupling electrode 4c and the coupling electrode 4d coupled thereto, the coupling electrode 4d and the output coupled thereto are provided. A voltage V1 corresponding to the vibration of the piezoelectric substrate 2 is generated between each of the electrodes 4b. Therefore, if the terminal TOUT1 is at the ground level, the first output electrode 4a is at the ground level, and a voltage V1 is generated between the first output electrode 4a and the coupling electrode 4c.
The potential of c becomes V1. Further, since the voltage V1 is also generated between the coupling electrode 4c and the coupling electrode 4d, the coupling electrode 4d
Is obtained by adding the voltage V1 to the potential V1 of the coupling electrode 4c.
V1. Further, the coupling electrode 4d and the second output electrode 4
Since the voltage V1 is also generated between the second electrode b and the second electrode b, the potential of the second output electrode 4b becomes 3V1 obtained by adding the voltage V1 to the potential 2V1 of the coupling electrode 4d. Therefore, a voltage 3V1 can be generated between the first output electrode 4a and the second output electrode 4b. As described above, according to the present embodiment, the first output electrode 4a and the second output electrode 4b are coupled to each other through the coupling electrodes 4c and 4d, which is three times the voltage V1 originally generated. Voltage 3V1 can be obtained, and the boost ratio can be increased. In this embodiment, three coupling gaps 5a, 5b, 5c are formed between the first output electrode 4a and the second output electrode 4b by two patterns of coupling electrodes 4c, 4d. Although the step-up ratio is three times higher, the step-up ratio is further increased by providing a larger number of coupling electrodes between the first output electrode 4a and the second output electrode 4b and increasing the number of coupling gaps. Can be done. For example, if the number of coupling gaps is m, the step-up ratio can be multiplied by m. FIG. 3 is a block diagram of a piezoelectric transformer according to a second embodiment of the present invention. In the figure, the same components as those of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, two pairs of input electrodes are formed in parallel. The input electrode 6 according to the present embodiment includes a first input electrode 6a, a second input electrode 6b, a third input electrode 6c, and a fourth input electrode 6d formed on the piezoelectric substrate 2. First input electrode 6a, second input electrode 6
b, the third input electrode 6c, and the fourth input electrode 6d are alternately arranged, the first input electrode 6a and the third input electrode 6c are connected integrally, and the second input electrode 6b and the fourth input electrode 6c are connected to each other. The input electrode 6d is integrally connected. The first and third input electrodes 6a and 6d are connected to an input terminal TIN1 connected to the ground, and the second and fourth input electrodes 6a and 6d are connected to the ground.
Input electrodes 6b and 6d are connected to an input terminal TIN2 to which a drive voltage is applied. The first to fourth input electrodes 6a to 6a
d, first and second output electrodes 4a, 4b, coupling electrode 4c,
The distance from 4d and the size of the piezoelectric substrate 2 are determined according to the oscillation frequency. FIG. 4 is a configuration diagram of a third embodiment of the piezoelectric transformer according to the present invention. In this embodiment, each of the input electrode and the output electrode is constituted by nine pairs of electrodes, and a pair of separation electrodes for input / output separation is provided between the input electrode and the output electrode. The input electrodes 7 of this embodiment are formed by alternately arranging linear electrodes 7a and 7b extending in the vertical direction in the figure on the piezoelectric substrate 2 in the horizontal direction in the figure. A voltage is applied, and the electrode 7b is grounded. The separation electrode 8 is formed on the surface of the piezoelectric substrate 2 on which the input electrode 7 is formed, adjacent to the input electrode 7, and a pair of linear electrodes 8a extending linearly in the vertical direction in the drawing. , 8
b are alternately arranged in the left-right direction in the figure, and both are grounded. Further, the output electrode 9 is the first output electrode 9
a, a second output electrode 9b, and coupling electrodes 9c and 9d. The first input electrode 9a is arranged on the upper side in the figure, and the second input electrode 9b is arranged on the lower side in the figure. The first output electrode 9a and the second output electrode 9b are coupled via coupling electrodes 9c and 9d, respectively, as in the first embodiment. The pitch of the input electrode 7, the separation electrode 8, and the output electrode 9 and the size of the piezoelectric substrate 2 are determined by the output voltage frequency. Here, for example, the length L of the piezoelectric substrate 2 is set to 15.2 mm corresponding to 19 wavelengths of the transverse wave, and the width W is set to 8 mm.
The width of the electrodes 7, 8, and 9 is 0.2 mm, and the distance between adjacent electrodes is 0.
If it is 1 mm, the piezoelectric substrate 2 resonates at 4.835 MHz. At this time, three times the voltage can be obtained between the output terminals of this embodiment as compared with the case where the output electrodes are formed in the same size and linearly. FIG. 5 shows a block diagram of a booster circuit using the piezoelectric transformer of the present invention. The booster circuit 11 includes a DC power supply 12, a drive circuit 13, a piezoelectric transformer 14, a feedback impedance 15, and an amplifier circuit 16. The piezoelectric transformer 14 is, for example, shown in FIGS.
Lithium niobate (LiN
The input / output electrodes 18 and 19 are formed on a piezoelectric substrate 17 of bO3) or the like. When a voltage of a predetermined frequency is applied to the input electrode 18 side, the piezoelectric transformer 14
7 resonates, and an output voltage is generated on the output electrode 19 side accordingly. FIG. 6 shows an equivalent circuit diagram of the piezoelectric transformer 14. The equivalent circuit of the piezoelectric transformer 14 includes an internal resistor R1, an inductance L1, and capacitors C1 to C3, and resonates with an input signal of a predetermined frequency. An input voltage is applied to the input electrode 18 of the piezoelectric transformer 14 from the drive circuit 13. Further, a feedback impedance 15 is connected between the piezoelectric transformer 14 and the drive circuit 13, and the input voltage fluctuation of the piezoelectric transformer 14 is supplied to the amplifier circuit 16 by the feedback impedance 15. The amplifier circuit 16 amplifies the input voltage fluctuation of the piezoelectric transformer 14 and supplies it to the drive circuit 13. The drive circuit 13 operates using the DC power supply 12 as a drive voltage, and supplies a drive voltage to the input electrode 18 of the piezoelectric transformer 14 according to a feedback signal supplied from the amplifier circuit 16. The piezoelectric transformer 14 resonates with the drive voltage of the drive circuit 13 and transmits energy to the output electrode 19. A load 20 is connected to the output electrode 19 and supplies power to the load 20. FIG. 7 is a circuit diagram showing a first embodiment of the booster circuit of the present invention. The drive circuit 13 includes N-channel field-effect transistors F1, F3, a P-channel field-effect transistor F2, and a resistor R11. The N-channel field effect transistor F1 constitutes an input transistor. The drain is connected to a DC power supply 12 via a resistor R11. The source is grounded. The gate 12 is supplied with a feedback signal from an amplifier circuit 16. A connection point between the drain of the N-channel field-effect transistor F1 and the resistor R11 is connected to a P-channel field-effect transistor F2 constituting an inverter.
And the gate of the N-channel field effect transistor F3. P-channel field effect transistors F2 and N
The connection point of the channel field effect transistor F3 is connected to the input electrode 18 of the piezoelectric transformer 14. In the drive circuit 13, the N-channel field-effect transistor F1 switches according to the feedback signal from the amplifier circuit 16, and the P-channel field-effect transistors F2 and N2 respond accordingly.
The switching of the channel field effect transistor F3 is controlled in reverse, and the drive signal is supplied to the first input electrode 18a of the piezoelectric transformer 17 by controlling the current supplied from the DC power supply 12. The first input electrode 18a of the piezoelectric transformer 17
Is grounded via a feedback impedance 15. In this embodiment, the feedback impedance 15 is constituted by a capacitor C1, and the input electrode 1 of the piezoelectric transformer
A signal having a level corresponding to the vibration generated in the piezoelectric transformer 1
4 and the capacitor C1. According to this embodiment, by providing the feedback impedance 15 composed of the capacitor C1, a feedback signal is obtained from the input electrode 18 side of the piezoelectric transformer 14, and the piezoelectric transformer 14 can be self-excited. Therefore, the inductor L1 of the piezoelectric transformer 14, the capacitors C1, C2,
Even if the value of C3 or the like fluctuates and the resonance frequency shifts, the drive signal can follow the shift, and the drive can always be performed in an optimum state. Therefore, isolation between the input electrode 18 side and the output electrode 19 side can be obtained. At this time, in this embodiment, since the capacitor C11 is used as the feedback impedance 15, the capacitor C11 is connected to the equivalent circuit of the piezoelectric transformer 14 shown in FIG.
4 slightly shifts from the case where only the piezoelectric transformer 14 is used. FIG. 8 is a circuit diagram of a booster circuit according to a second embodiment of the present invention. 5, the same components as those in FIGS. 5 and 7 are denoted by the same reference numerals, and the description thereof will be omitted. In this embodiment, the feedback impedance 15 is constituted by the inductance L11, and the other components are the same as those shown in FIG. In this embodiment, since the feedback impedance 15 is formed by the inductor L11, the equivalent circuit of the piezoelectric transformer 14 shown in FIG.
Is added, the resonance frequency of the piezoelectric transformer 14 shifts in the opposite direction to that of the capacitor C11. FIG. 9 shows a block diagram of a booster circuit according to a third embodiment of the present invention. 5, the same components as those in FIGS. 5, 7, and 8 are denoted by the same reference numerals, and description thereof will be omitted. This embodiment uses a resistor R12 as the feedback impedance 15 shown in FIGS. 5, 7, and 8. By using the resistor R12, the resonance frequency f0 of the piezoelectric transformer 14 is not affected, and the resonance frequency f0 of the feedback impedance 15 is not affected.
Does not occur. At this time, the loss can be reduced by reducing the value of the resistor R12. FIG. 10 shows a frequency characteristic diagram of the booster circuit.
In the figure, a broken line indicates the use of the capacitor C11 as the feedback impedance 15, a dashed line indicates the use of the inductor L11, and a solid line indicates the use of the resistor R12. The characteristics using the capacitor C11 shift to the high frequency side, and the characteristics using the inductor L11 shift to the low frequency side, and both of them can be driven at the maximum voltage without any loss. The characteristics using the resistor R12 do not shift. According to the above-described booster circuit 11, a high-frequency output of about 5 MHz can be easily obtained. FIG. 11 is a block diagram showing a first embodiment of the discharge tube lighting device according to the present invention. In this embodiment, the discharge tube 21
Are connected to, for example, a load 20 of the booster circuit 11 shown in FIGS. 5, 7, and 9, and are driven at a high frequency of several MHz. At this time, for example, the piezoelectric transformer 1 shown in FIGS. 1, 3, and 4 is used as the piezoelectric transformer 14. With the above configuration, the discharge tube 21 is driven at a high frequency of several MHz to realize lighting at a low voltage. FIG. 12 is a diagram for explaining the lighting operation. Discharge tube 2
As shown in FIG. 12A, an Ar gas is sealed at a gas pressure of 20 Torr in a glass tube 23 coated with a fluorescent film 22 on its inner surface as shown in FIG. The discharge tube 21 shown in FIG.
By driving at a high frequency, the cathode drop voltage for accelerating the electrons e can be reduced, and plasma can be excited from the vicinity of the electrode 24, so that a potential distribution as shown in FIG. 12B can be obtained. FIG. 13 is an operation explanatory diagram when the discharge tube 21 is driven at a low frequency of about 30 kHz. When the discharge tube 21 is driven at a low frequency, a dark portion exists near the cathode, where electrons are accelerated to excite plasma, and the acceleration voltage (cathode drop voltage) does not contribute to light emission. In the case of, the ratio of the occupancy becomes large. This is based on the materials of the Japan Institute of Illumination Study Group (Light Generation and Related Systems Study Group “Recent Trends of Fluorescent Lamps” LS-92-
1-6, February 27, 1992, Lighting Information Session,
See Trends in Fluorescent Lamps for Backlights, Masayuki Kobayashi and Yuji Danno). As described above, according to the present embodiment, since the cathode drop voltage can be reduced, the discharge tube can emit light with high efficiency. FIGS. 14 and 15 are explanatory diagrams of the operation of this embodiment. FIG. 14 (A) shows a tube diameter of 8 mm and an Ar gas pressure of 20 To.
14B shows the potential distribution of a cold cathode tube having a tube diameter of 6 mm and an Ar gas pressure of 10 Torr. FIG.
The pipes shown in Fig. 4 have a pipe length of 80 mm and a pipe length of 100, respectively.
3 shows the frequency dependence of the luminous efficiency of a mm tube. The tube voltage in FIG. 14 is the product of the measured value V and the power factor cos φ. FIG.
The luminous efficiency at 5 is standardized by the luminance of each tube measured at 40 kHz. According to these data, it is apparent that the cathode drop voltage is reduced above a certain frequency (MHz band), and the luminous efficiency is improved. FIG. 16 is a block diagram of a discharge tube lighting device according to a second embodiment of the present invention. In the figure, the same components as those of FIG. 11 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, a feedback circuit 22 is provided on the output electrode 19 side of the piezoelectric transformer 14, a feedback signal is generated by the feedback circuit 22, and self-excitation is performed by controlling the drive circuit 13. The feedback circuit 22 includes resistors R21 and R2.
2, consisting of an amplifier 23 and a phase adjustment circuit 24. In the feedback circuit 22, the voltage fluctuation of the output electrode 14 of the piezoelectric transformer 14 is reduced by the resistors R21 and R22, then amplified by the amplifier 23, and the phase is adjusted by the phase adjustment circuit 24 so that oscillation occurs. Drive circuit 1
Supply 3 As described above, since self-excited vibration is performed by the piezoelectric transformer 14, a high-frequency voltage of several MHz can be applied to the discharge tube 21. In FIGS. 11 and 16, the piezoelectric transformer 1
4 is assumed to have the power supply structure shown in FIG. 1, FIG. 3, and FIG. 4, but is not limited thereto, and can be realized by other electrodes or a piezoelectric transformer having a crystal structure of a piezoelectric substrate. It is sufficient that a high frequency voltage of MHz can be applied to the discharge tube 21. FIG. 17 is a block diagram showing a third embodiment of the discharge tube lighting device according to the present invention. 15, the same components as those of FIG. 15 are denoted by the same reference numerals, and the description thereof will be omitted. In this embodiment, a resonance circuit 31 composed of a coil L21 and a capacitor C21 is used as high-frequency high-voltage generating means. In this embodiment, the voltage V2 applied to the discharge tube 21 is represented by V2 = Q.V1 where V1 is the input voltage and Q is the quality factor of the resonance circuit 31. FIG. 18 is a block diagram of a discharge tube lighting device according to a fourth embodiment of the present invention. 16, the same components as those in FIGS. 16 and 17 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, a resonance circuit 42 using a resonator 41 and a capacitor C31 is used as high-frequency high-voltage generating means. FIG. 19 shows an equivalent circuit diagram of the resonator 41. The resonator 41 is composed of an equivalent capacitance C0, an additional capacitance Cd, and an inductance L, and resonates at a frequency determined by the above factors. In this embodiment, the voltage V2 applied to the discharge tube 21 is the input voltage V1, the discharge tube 21 and the resonance circuit 42.
Assuming that the quality factor of the resonance system is Q, the equivalent capacitance of the resonator 41 is C0, and the capacitance of the external capacitor C31 is C1, V2 = QV1C0 / (C1 + C0). As described above, according to the present invention, since the self-oscillation is performed by the signal fed back from the input electrode side, the self-oscillation can be performed while isolating the input / output electrodes. It has features such as being able to.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a first embodiment of a piezoelectric transformer according to the present invention. FIG. 2 is an operation explanatory view of a first embodiment of the piezoelectric transformer of the present invention. FIG. 3 is a configuration diagram of a second embodiment of the piezoelectric transformer according to the present invention. FIG. 4 is a configuration diagram of a third embodiment of the piezoelectric transformer of the present invention. FIG. 5 is a block diagram of a first embodiment of the booster circuit of the present invention. FIG. 6 is an equivalent circuit diagram of a piezoelectric transformer. FIG. 7 is a circuit configuration diagram of a first embodiment of the booster circuit of the present invention. FIG. 8 is a circuit diagram of a booster circuit according to a second embodiment of the present invention. FIG. 9 is a circuit configuration diagram of a third embodiment of the booster circuit of the present invention. FIG. 10 is a frequency characteristic diagram of the booster circuit of the present invention. FIG. 11 is a block diagram of a first embodiment of the discharge tube lighting device of the present invention. FIG. 12 is a diagram illustrating the operation of the discharge tube lighting device of the present invention. FIG. 13 is an explanatory diagram of an operation of the discharge tube in low-frequency driving. FIG. 14 is an operation explanatory view of the first embodiment of the discharge tube lighting device of the present invention. FIG. 15 is an operation explanatory view of the first embodiment of the discharge tube lighting device of the present invention. FIG. 16 is a configuration diagram of a second embodiment of the discharge tube lighting device of the present invention. FIG. 17 is a configuration diagram of a discharge tube lighting device according to a third embodiment of the present invention. FIG. 18 is a configuration diagram of a fourth embodiment of the discharge tube lighting device according to the present invention. FIG. 19 is an equivalent circuit diagram of a resonator. FIG. 20 is a configuration diagram of an example of a piezoelectric transformer. [Description of Signs] 1 piezoelectric transformer 2 piezoelectric substrate 3 input electrode 4 output electrode 4a first output electrode 4b second output electrode 4c, 4d coupling electrode 11 booster circuit 12 DC power supply 13 drive circuit 14 piezoelectric transformer 15 feedback impedance 16 amplifier circuit 21 discharge tube

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Hidenori Fukushima             1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa             Fujitsu Limited

Claims (1)

Claims: 1. An input voltage is applied to an input electrode formed on a piezoelectric substrate to vibrate the piezoelectric substrate, and output from an output electrode formed on the piezoelectric substrate in response to the vibration. In a piezoelectric transformer for obtaining a voltage, a detection impedance connected to the input electrode and detecting a feedback signal according to a displacement of the input voltage from a connection point with the input electrode; and a detection impedance of the detection impedance and the input electrode. A drive circuit for displacing the input voltage in accordance with a feedback signal obtained from a connection point, performing feedback by a feedback signal from the input electrode side, and performing self-excitation while maintaining isolation between input and output. A piezoelectric transformer characterized by the following.