JP2000050646A - Drive circuit for piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the heat loss of a piezoelectric transformer which inputs an AC voltage from primary electrodes and outputs a transformed voltage from secondary electrodes through the utilization of piezoelectric effect by driving the transformer with a transformed voltage of the transformer. SOLUTION: An input power control section 20 controls drive voltages vd1 and vd2 which are generated from primary electrodes 401 and 402 of a piezoelectric transformer 40, so that they do not depend on a power supply voltage Vcc. When a resonance circuit is formed of the inductance of a coil 33 and the equivalent capacity between the primary electrodes 401 and 402 of the transformer 40, a transistor 21 is normally turned off and the current path going toward the primary electrode 401 from a power source 10 through the coil 33 is disconnected. Similarly, when a resonance circuit is formed of the inductance of a coil 34 and the equivalent capacity between the primary electrode 401 and 402 of the transformer 40, a transistor 22 is normally turned off, and the current path going toward the primary electrode 402 fro the power source 10 through the coil 34 is disconnected. Therefore, an excess current can be prevented from flowing in the transformer, and the heat loss of the transformer 40 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for supplying AC and high-voltage power to a certain load using a DC power supply voltage, and more particularly to a power supply circuit using a driving circuit for a piezoelectric transformer.

[0002]

2. Description of the Related Art Generally, to drive a certain load,
It is necessary to convert a DC power supply voltage into AC and high-voltage power.

Conventionally, an electromagnetic transformer type inverter has been frequently used as an electric circuit for converting a DC power supply voltage into AC and high-voltage power. However, the use of an electromagnetic transformer-type inverter results in a large-scale, large-mass, and low-efficiency electric circuit, which is a major obstacle to reducing the size, mass, and efficiency of the machine on which the electric circuit is mounted. Was.

In recent years, there has been an increasing demand for downsizing, downsizing, and low power consumption of inverters, and piezoelectric transformer type inverters having small size, small mass, and high efficiency have attracted attention. In addition, a cold-cathode tube inverter, which is well known as a specific example, requires a small-sized and high-efficiency, and means for keeping the tube current flowing through the cold-cathode tube constant in order to keep the luminance constant.

FIG. 14 shows a conventional piezoelectric transformer driving circuit. The piezoelectric transformer 40 converts the AC voltage vpt applied between the primary electrode 401 and the primary electrode 402 into an AC voltage vo having a different amplitude from vpt using a piezo effect,
An element for outputting to the secondary electrode. The step-up ratio Av of the piezoelectric transformer (Av is the amplitude ratio of the AC voltage value of vo output to the secondary electrode of the piezoelectric transformer with respect to the AC voltage value of vpt input between the primary electrodes) is as shown in FIG. 2B. At the resonance frequency fo of the piezoelectric transformer, the resonance frequency f
It decreases as one moves away from o. Further, the boost ratio Av of the piezoelectric transformer increases as the load impedance RL increases, as shown in FIG. 2D. Therefore, the driving circuit of the piezoelectric transformer needs a means for keeping the load current iol flowing through the load constant with respect to the fluctuation of the load impedance RL and the temperature change of the load.

A conventional piezoelectric transformer drive circuit is shown in FIG.
As shown in FIG.
An input power control unit 120 composed of an input power control circuit 123, a diode 131, a coil 132, and a coil 1;
A drive voltage generator 130 composed of 33, a transistor 134, and a transistor 135; a current-voltage converter 161; a voltage control oscillator 162; and a drive control circuit 163.
A buffer 164, a frequency control unit 160 including a buffer 165, a drive voltage detection circuit 170, a piezoelectric transformer 40, and a load 50. Due to the configuration of the driving circuit for the piezoelectric transformer, the driving circuit for the piezoelectric transformer includes the primary electrodes 401 and 402 of the piezoelectric transformer 40.
During this period, an AC voltage vpt is generated to drive the piezoelectric transformer 40, and the load current iol is controlled to be constant.

The frequency control unit 160 shown in FIG. 14 controls the transistors 134 and 13 so that the value of the tube current iol flowing out from the low voltage terminal 502 of the load becomes constant.
5 is a block for controlling the frequency of the pulse voltage output to each of the gates 1341 and 1351. The impedance R of the load 50 is determined by the frequency control unit 160.
With respect to the fluctuation of L and the temperature change of the load 50, the load current io
l can be kept constant, that is, the luminance of the load can be kept constant.

The primary electrode 401 of the piezoelectric transformer 40
And an energy efficiency value η for transmitting power supplied between the primary electrode 402 of the piezoelectric transformer 40 to the secondary electrode 403.
Is largest near the resonance frequency fo of the piezoelectric transformer as shown in FIG. 2A, and decreases as the distance from the resonance frequency fo increases. When a constant voltage vo is supplied to the load 50, the relationship between the driving voltage vd1 and the driving voltage vd2 generated at each of the primary electrode 401 of the piezoelectric transformer and the primary electrode 402 of the piezoelectric transformer and the driving voltage frequency is shown in FIG. 2B. FIG. 2C shows the boost ratio Av and the frequency characteristic of the piezoelectric transformer 40 shown in FIG.

In the drive circuit shown in FIG. 14, a primary electrode 401 of the piezoelectric transformer and a primary electrode 402 of the piezoelectric transformer
Between the coil 132 and the coil 1
When the inductances of the piezoelectric transformers 33 are set to be equal to each other, the primary electrode 401 of the piezoelectric transformer 40 and the piezoelectric transformer 40
Drive voltage vd1 generated at each of the primary electrodes 402
The drive voltage vd2 is an approximate half-wave sine wave having an amplitude about three times the power supply voltage value Vcc. Therefore, the amplitudes of the drive voltage vd1 and the drive voltage vd2 are equal to the power supply voltage value V
It increases in proportion to cc. Therefore, in order to drive the piezoelectric transformer 40 with high efficiency, the drive circuit needs to have the power supply voltage V
The frequency range in which the value of the energy efficiency η of the piezoelectric transformer 40 is large with respect to the increase in cc (frequency f1 or more and f2
Means for driving the piezoelectric transformer 4
A means for reducing the amplitude of the drive voltage vd1 and the drive voltage vd2 input to 0 to a fixed value vd or less is required.

The input power control unit 120 shown in FIG. 14 includes a coil 132 and a coil 133 of the drive voltage generation unit 130.
To control the current flowing through the primary electrode 4 of the piezoelectric transformer 40.
01 and the amplitudes of the drive voltage vd1 and the drive voltage vd2 input to the primary electrode 402 of the piezoelectric transformer 40 are controlled.
From the timing chart shown in FIG.
21 is always on, the drive voltage vd1 and the drive voltage v
The amplitude of d2 is about three times the power supply voltage.

[0011] As shown in FIG.
When the on / off switching operation of the transistor 121 is performed at twice the frequency of the on / off switching operation of the transistor 135, and the time during which the transistor 121 is turned on is shortened, the coil 132 is turned on compared with the case where the transistor 121 is always on. In addition, the electromagnetic energy stored in the coil 133 decreases, and the amplitudes of the drive voltage vd1 and the drive voltage vd2 decrease.

As shown in FIG. 14, the driving circuit includes a driving voltage vd generated at the primary electrode 401 of the piezoelectric transformer 40.
1 is detected by the drive voltage detection circuit 170, and the ON / OFF time of the transistor 121 is controlled so that the drive voltage vd1 and the drive voltage vd2 do not exceed a value vd arbitrarily set regardless of the rise of the power supply voltage Vcc. Change the ratio. Even when the power supply voltage Vcc is increased by the input power control unit 120, the drive circuit holds the amplitudes of the drive voltage vd1 and the drive voltage vd2 at a constant value vd, and the drive voltage frequency f1 or more f2 at which the energy efficiency value η is always large. The piezoelectric transformer 40 can be driven in the following range.

However, when the above operation is performed in the input power control circuit 123, the primary electrode 401 of the piezoelectric transformer 40 or the primary electrode of the piezoelectric transformer 40 in which a drive voltage is generated by resonance during the time when the transistor 121 is turned on. A current path is formed between the electrode 402 and the power supply 10. In this case, the primary electrode 40 of the piezoelectric transformer 40 is
1 or il1 and il2 in FIG.
Inflow like. The excess current flows through the load 50
Are not supplied to the transistor 121 and the transistor 1
Since heat loss occurs due to the on-resistance of the transistor 34 and the transistor 135, the efficiency of the drive circuit is reduced. Further, as shown in FIG.
Since the maximum current of each of the currents iq1 and iq2 flowing through the circuit increases, it is necessary to use a transistor having a high rated current, which makes it difficult to reduce the size, mass, and cost of the drive circuit. Further, in this case, as shown in FIG. 16, the drive voltage vd1 and the drive voltage vd2 are distorted,
The high frequency component of the voltage vpt input between the primary electrode 401 and the primary electrode 402 of the piezoelectric transformer 40 increases, and as a result, unnecessary vibration of the piezoelectric transformer 40 occurs, which causes deterioration and breakage of the piezoelectric transformer 40. Becomes

In order to solve such a problem, Japanese Patent Application Laid-Open No. 9-219292 discloses a cold cathode using a phase shift circuit for changing the voltage phase so that the output voltage of a piezoelectric transformer becomes a set voltage. A tube lighting inverter is disclosed. According to this cold-cathode tube lighting inverter, even when the output voltage changes, the oscillation frequency is controlled so that a predetermined output voltage can always be obtained, and the cold-cathode tube lighting inverter that maintains stable brightness. It can be provided.

In addition, for the purpose of solving the problems of the prior art, Japanese Patent Application Laid-Open No. 9-63778 discloses that a current limiting resistor is connected in series between an output of a driving circuit and an input electrode of a piezoelectric transformer. A piezoelectric transformer type cold-cathode fluorescent lamp driving device characterized by the following is disclosed. According to this piezoelectric transformer type cold cathode fluorescent lamp driving device, it is said that pulsation can be suppressed by making the value of the current flowing through the cold cathode fluorescent lamp substantially constant.

[0016]

However, Japanese Patent Laid-Open No. 9-2
The inverter for cold-cathode lighting using the phase shift circuit that changes the phase of the voltage of No. 19292 has a mechanism for suppressing and controlling the current from the power supply when the current from the power supply flows into the piezoelectric transformer. And there may still be excess current from the power supply. Therefore, it is hard to recognize that the efficiency of the driving circuit of the piezoelectric transformer is improved. In addition, the piezoelectric transformer type cold cathode fluorescent lamp driving device disclosed in Japanese Patent Application Laid-Open No. 9-63778 does not have a mechanism for suppressing and controlling the current from the power supply when the current from the power supply flows into the piezoelectric transformer. Excess current from the power supply may be present.
Therefore, it is hard to recognize that the efficiency of the driving circuit of the piezoelectric transformer is improved. In order to solve this problem, the present invention increases the amplitude of an AC voltage to make the current flowing through a load constant, and adjusts the voltage input between the primary electrodes of the piezoelectric transformer to drive the piezoelectric transformer with high efficiency. It is another object of the present invention to reduce the unnecessary vibration of the piezoelectric transformer and the heat loss of the transistor and the diode by maximizing the step-up ratio of the piezoelectric transformer and reducing the excessive current flowing into the drive voltage generator.

Further, the structure of the phase shift circuit of the inverter for lighting between the cold cathodes using the phase shift circuit for changing the phase of the voltage disclosed in Japanese Patent Application Laid-Open No. 9-219292 is similar to that of an induction motor. As can be seen from the structure in which a series winding with a large current is distributed on the stator side and a shunt winding is provided on the winding rotor side, the size of the device tends to be large and it is difficult to reduce the size easily. Have. Therefore,
It is difficult to reduce the size of the piezoelectric transformer drive circuit. In order to solve this problem, the present invention eliminates the need to use a transistor with a high rated current by reducing the inflow of excessive current into the drive voltage generating unit. It is an object to achieve downsizing of a drive circuit of a transformer.

[0018]

According to a first aspect of the present invention, there is provided a driving circuit for driving a piezoelectric transformer, comprising: an input power control section for inputting power from a DC power supply; and an input power control section for inputting power from the input power control section. A driving voltage generator for outputting an AC voltage, a frequency controller for controlling the frequency of the AC voltage, a driving voltage detecting circuit for detecting a voltage generated by the driving voltage generator, and an AC voltage input from a primary electrode. A piezoelectric transformer that outputs an AC voltage from the secondary electrode using the piezoelectric effect, and a load that is driven by the electric power transformed by the piezoelectric transformer.

Therefore, according to the piezoelectric transformer drive circuit of the first invention of the present application, in the input power control section,
The power supplied from the DC power supply to the drive voltage generator is controlled by an input signal from the frequency controller. The driving voltage generator receives the power input from the input power controller and converts the input power into an AC voltage. The drive voltage detection circuit detects a value of an AC voltage generated in the drive voltage generation unit, and inputs the voltage value to the input power control unit. That is, the input power control unit controls power supplied from the power supply to the drive voltage generation unit according to input signals from the frequency control unit and the drive voltage detection circuit. Also, the piezoelectric transformer drive circuit of the present invention applies the AC voltage generated by the drive voltage generator to the primary electrode of the piezoelectric transformer, and as a result, boosts the voltage at the primary electrode to the secondary electrode by the piezoelectric effect. Voltage is generated,
The voltage is applied to a load.

According to a second aspect of the present invention, in the driving circuit device for a piezoelectric transformer according to the first aspect of the present invention, the input power control section comprises a transistor, a buffer, and an input power control circuit.

Therefore, according to the piezoelectric transformer drive circuit of the second invention of the present application, the input power control section adjusts the power supplied from the power supply to the drive voltage generation section by switching the transistor on and off. . The input power control circuit transmits a signal to a transistor through an output buffer based on an input signal from the frequency control unit and the drive voltage detector. By these series of operations, an excessive current to the drive voltage generating section is suppressed.

According to a third aspect of the present invention, there is provided a driving circuit device for a piezoelectric transformer according to the first or second aspect of the present invention.
The driving voltage generator includes a diode, a coil, and a transistor.

Therefore, according to the piezoelectric transformer drive circuit of the third invention of the present application, the drive voltage generation section switches the transistor on and off based on the input signal from the frequency control section, thereby providing the power supply. A resonance circuit is formed by the diode, the coil, and the piezoelectric transformer using the energy stored in the coil from, and as a result, a sine wave voltage is generated.

According to a fourth aspect of the present invention, in the driving circuit device for a piezoelectric transformer according to any one of the first to third aspects of the present invention, the frequency control section includes a current-voltage conversion circuit and a voltage-controlled oscillation circuit. And a drive control circuit and a buffer.

Therefore, according to the piezoelectric transformer driving circuit of the fourth invention of the present application, the frequency control section inputs the current flowing from the load to the current-voltage conversion circuit, converts the current into a DC voltage, and outputs the DC voltage. Then, the DC voltage is input to a voltage controlled oscillation circuit to generate a pulse by changing the frequency according to the magnitude of the input voltage, and the pulse is input to the drive control circuit to generate a sine wave between the primary electrodes. By shifting the pulse phase by 180 degrees to generate a voltage waveform and outputting the pulse to a buffer and an input voltage control unit, the frequency of the pulse is controlled to keep the drive voltage stable and constant.

According to a fifth aspect of the present invention, in the driving circuit device for a piezoelectric transformer according to any one of the first to fourth aspects of the present invention, the input power control section comprises two transistors and buffers for each of the transistors. Are provided one by one, and each of the buffers is connected to an input power control circuit.

Therefore, according to the piezoelectric transformer drive circuit of the fifth invention of the present application, the input power control unit connects one transistor to each coil of the drive voltage generation unit, and each of the transistors is connected to an input terminal. It is controlled by a pulse voltage coming from the power supply control circuit through the buffer. The input power control unit controls the two coils by using the respective transistors separately,
Excessive current from the power supply can be suppressed, and the piezoelectric transformer can be driven with high efficiency. Further, the input power control section reduces the heat loss due to the on-resistance of the transistor and the heat loss of the diode by reducing the excess current from the power supply.

According to a sixth aspect of the present invention, there is provided a driving circuit device for a piezoelectric transformer according to any one of the first to fifth aspects of the present invention, wherein the driving voltage generator comprises two diodes and a coil for each of the diodes. Are provided one by one, and one transistor is provided for each of the coils.

Therefore, according to the piezoelectric transformer drive circuit of the sixth aspect of the present invention, the drive voltage generating section independently combines two circuits each having a set of a diode, a coil, and a transistor, thereby forming each of the circuits. An AC voltage generated by the coil can be independently controlled in each of the two primary electrodes of the piezoelectric transformer, so that an approximate sine wave is input between the primary electrodes. .

According to a seventh aspect of the present invention, in the driving circuit device for a piezoelectric transformer according to any one of the first to sixth aspects of the present invention, the frequency control unit includes a current-voltage conversion circuit and a voltage-controlled oscillation circuit. And a drive control circuit and two buffers connected to the drive control circuit.

Therefore, according to the piezoelectric transformer drive circuit of the seventh aspect of the present invention, the frequency control section inputs the current flowing from the load to the current-voltage conversion circuit, converts the current into a DC voltage, and outputs the DC voltage. Then, the DC voltage is input to a voltage controlled oscillation circuit, a frequency is changed according to the magnitude of the input voltage to generate a pulse, and the pulse is input to a drive control circuit to generate a pulse.
In order to generate a voltage close to a sine wave between the next electrodes, the pulse phase is changed by 180 degrees, the frequency of the pulse is controlled, and the pulse is connected to two buffers respectively connected to two transistors of the driving voltage generating unit. 2 for input voltage control
By connecting and outputting two paths, a total of four of the two transistors of the input voltage control unit and the two transistors of the drive voltage generation unit can be independently controlled, and the drive voltage is stabilized and fixed. To keep.

According to an eighth aspect of the present invention, in the drive circuit device for a piezoelectric transformer according to any one of the first to seventh aspects of the present invention, the values of the inductances of the two coils in the drive voltage generating section are mutually determined. It is characterized by being substantially equal.

Therefore, the drive circuit for the piezoelectric transformer according to the eighth aspect of the present invention provides a resonance circuit formed by the coil and the piezoelectric transformer by making the inductance values of the two coils in the drive voltage generating section substantially equal to each other. The voltage excited by the circuit can be made substantially the same value at the two primary electrodes of the piezoelectric transformer.

According to a ninth aspect of the present invention, in the driving circuit device for a piezoelectric transformer according to any one of the first to eighth aspects of the present invention, the input power control circuit provided in the input power control section comprises a drive. It is characterized by outputting a signal in which the time ratio between the high-level voltage portion and the low-level voltage portion of the pulse voltage rectangular wave input from the voltage detection circuit is changed.

Therefore, according to the piezoelectric transformer drive circuit of the ninth aspect of the present invention, the input power control circuit provided in the input power control unit is a pulse voltage rectangular input from the drive control circuit of the frequency control unit. By outputting a signal in which the time ratio between the high-level voltage portion and the low-level voltage portion of the wave is changed, it is possible to keep the drive voltage in the drive voltage generation section constant. As a result, the piezoelectric transformer driving circuit according to the present invention can drive the piezoelectric transformer in a frequency range where the energy efficiency of the piezoelectric transformer is high.

According to a tenth aspect of the present invention, in the driving circuit device for a piezoelectric transformer according to any one of the first to ninth aspects of the present invention, one of the two transistors provided in the input voltage control section is provided. Is set to be shorter than the time during which two transistors provided in the drive voltage generation section are turned on or off.

Therefore, the driving circuit of the piezoelectric transformer according to the tenth aspect of the present invention is configured such that the time during which one of the two transistors provided in the input voltage control unit is turned on is equal to the time required for the two transistors provided in the drive voltage generation unit. The drive voltage of the piezoelectric transformer can be adjusted so that the energy efficiency of the piezoelectric transformer is maximized by setting the time shorter than the time when the transistor is turned on or off. At the same time, the present invention can prevent an excessive current from flowing from the power supply 10 to the drive voltage generation unit.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a driving circuit of a piezoelectric transformer according to the present invention will be described below with reference to FIGS. 1, 3, 4, 5, 6, 6, 7, 8, 9, 10, and 10. FIG. 11, FIG.
2, description will be given based on FIG.

Embodiment 1 FIG. 1 is a circuit diagram of a driving circuit for a piezoelectric transformer according to an embodiment of the present invention. As shown in FIG. 1, the driving circuit of the piezoelectric transformer includes an input power control unit 20 composed of a transistor 21, a transistor 22, a buffer 23, a buffer 24, and an input power control circuit 25, a diode 31, a diode 32, and a coil 33. A drive voltage generation unit 30 composed of a coil 34 and a transistor 35; a transistor 36; a current-voltage conversion circuit 61; a voltage control oscillation circuit 62; a drive control circuit 63;
The frequency control unit 60 includes a buffer 65, a drive voltage detection circuit 70, a piezoelectric transformer 40, and a load 50. In this embodiment, a transistor can be, for example, a field-effect transistor or a bipolar transistor, and a diode can be, for example, a Schottky barrier diode, and a piezoelectric transformer is, for example, a Rosen secondary type single plate type. A Rosen secondary type laminated type, Rosen tertiary type single plate type, Rosen tertiary type laminated type and the like can be used, and the load can be a cold cathode tube or the like. As for the load, a device for charging the toner of the copying machine, a device for flashing the camera, and the like can be used.

The configuration of the input power control unit 20 shown in FIG. 1 will be described in detail. The source 214 of the transistor 21 is connected to the power supply 10
And the drain 212 of the transistor 21 is connected to the diode 3
The gate 211 is connected to the output of the buffer 23 at one cathode 312 and one end 331 of the coil 33. The diode 213 is a parasitic diode of the transistor 21.
The transistor 21 is connected to the power supply 10 and the cathode 31 of the diode 31 by the pulse voltage input from the buffer 23.
2 and one end 331 of the coil 33 are connected or disconnected.

The source 224 of the transistor 22 is connected to the power supply 1
0, the drain 222 is connected to the cathode 32 of the diode 32.
2 and one end 341 of the coil 34, the gate 221 is connected to the buffer 24. The diode 223 is a parasitic diode of the transistor 22. The transistor 22 connects or cuts off between the power supply 10 and the cathode 322 of the diode 32 and one end 341 of the coil 34 according to the pulse voltage input from the buffer 24.

The input terminals 251 and 252 of the input power control circuit 25 are connected to the output terminal 632 of the drive control circuit 63.
And the input terminal 253 is connected to the output terminal 633 and the output terminal 702 of the drive voltage detection circuit 70. The output terminal 254 and the output terminal 255 of the input power control circuit 25 are connected to the buffer 23 and the buffer 24. Input power control circuit 2
5 is an output terminal 63 of the drive control circuit 63 according to the voltage value input from the output terminal 702 of the drive voltage detection circuit 70.
2 and a time ratio between the high level and the low level of the pulse voltage input from the output terminal 633 and output to the buffers 23 and 24. Buffer 23 and Buffer 2
Reference numeral 4 denotes a pulse voltage output from the output terminals 254 and 255 of the input power control circuit 25,
1 and a voltage that can drive the transistor 22.

The input power control unit 20 includes a piezoelectric transformer 40
Primary electrode 401 and the primary electrode 40 of the piezoelectric transformer 40
2 is controlled so as to be equal to or less than an arbitrary value without depending on the power supply voltage value Vcc. In addition, the input power control unit 20 includes the transistor 2
When a drive voltage is generated in the primary electrode 401 of the piezoelectric transformer 40 by 1, the current path from the power supply 10 to the primary electrode 401 is cut off by turning off the transistor 21. Therefore, the driving circuit of this piezoelectric transformer
A resonance circuit is formed by the coil 33, the piezoelectric transformer 40, the transistor 36, and the diode 31, or a resonance circuit is formed by the transistor 36, the piezoelectric transformer 40, the coil 33, the parasitic diode 213, and the power supply 10. Similarly, the input power control unit 20 controls the primary electrode 402 of the piezoelectric transformer 40.
When a driving voltage is generated, the current path from the power supply 10 to the primary electrode 402 is cut off by turning off the transistor 22. Therefore, the driving circuit of the present piezoelectric transformer forms a resonance circuit with the coil 34, the piezoelectric transformer 40, the transistor 35, and the diode 32, or forms a resonance circuit with the transistor 35, the piezoelectric transformer 40, the coil 34, the parasitic diode 223, and the power supply 10. I do.

Hereinafter, the operation of the input power control unit 20 will be described. The input power control circuit 25 controls the time ratio between the high level and the low level of the pulse voltage input to the input terminals 251 and 252 so that the DC voltage input from the drive voltage detection circuit 70 becomes equal to or less than an arbitrary value. To change.
The input power control circuit 25 outputs this pulse voltage to the buffers 23 and 24, respectively. The input power control circuit 25 drives the transistors 21 and 22 with the pulse voltages amplified by the buffers 23 and 24. When the amplitude of the driving voltage is smaller than an arbitrarily set value (here, vd), the timing chart of the transistors 21 and 22 is as shown in FIG. 3, and the amplitude of the driving voltage vd1 and the driving voltage vd2 is It is about twice the voltage Vcc. On the other hand, if the amplitude of the drive voltage is to become larger than the value vd arbitrarily set, the timing chart of the transistors 21 and 22 is as shown in FIG. 4, and the amplitudes of the drive voltage vd1 and the drive voltage vd2 are equal to the power supply voltage Vcc. Constant value vd regardless of
Becomes Due to the above operation of the input power control unit 20, the amplitudes of the drive voltage vd1 and the drive voltage vd2 of the piezoelectric transformer become equal to or less than vd regardless of the power supply voltage Vcc. Therefore, by setting this arbitrary value vd equal to the value vd shown in FIG. 2C, the driving circuit of the piezoelectric transformer is always driven in the frequency range where the energy efficiency value η of the piezoelectric transformer is large (f1 or more and f2 or less). be able to.

The configuration of the drive voltage generator 30 will be described in detail. One end 331 of the coil 33 is connected to the cathode 312 of the diode 31 and the drain 212 of the transistor 21. The anode 311 of the diode 31 is connected to the ground. The other end 332 of the coil 33 is connected to the drain 352 of the transistor 35, the primary electrode 401 of the piezoelectric transformer 40, and the input terminal 701 of the drive voltage detection circuit 70.
The source 354 of the transistor 35 is connected to the ground, and the gate 351 is connected to the output of the buffer 64. Diode 3
53 is a parasitic diode of the transistor 35. The transistor 35 is connected to the terminal 332 of the coil 33, the primary electrode 401 of the piezoelectric transformer 40, and the input terminal 7 of the drive voltage detection circuit 70 by the pulse voltage output from the buffer 64.
01 or ground is connected or cut off.

The one end 341 of the coil 34 is connected to the diode 32
Cathode 322 and the drain 22 of the transistor 22
Connect to 2. The anode 321 of the diode 32 is connected to the ground. The other end 342 of the coil 34 is connected to the drain 362 of the transistor 36 and the primary electrode 402 of the piezoelectric transformer 40. Source 364 of transistor 36
To the ground, and the gate 361 to the output of the buffer 65. The diode 363 is a parasitic diode of the transistor 36. The transistor 36 is connected to the terminal 342 of the coil 34 by the pulse voltage output from the buffer 65.
And a connection or cutoff between the primary electrode 402 of the piezoelectric transformer 40 and the ground. As shown in FIG. 1, the secondary electrode 403 of the piezoelectric transformer 40 is connected to the high voltage terminal 501 of the load 50.

Next, the operation of the drive voltage generator 30 will be described. FIG. 3 shows a timing chart in the case where the on-time and the off-time of the transistor 21 and the transistor 22 are equal. In FIG. 3, the current il1 is
From the one end 331 to the other end 332,
The current il2 is a current flowing from one end 341 of the coil 34 to the other end 342. The current iq1 is the transistor 35
The current iq2 is a current flowing from the drain 352 of the transistor 36 toward the source 354.
Is a current flowing from the source to the source 364. Also, the voltage v
d1 is a drive voltage generated between the intersection of the drain 352 of the transistor 35, the primary electrode 401 of the piezoelectric transformer 40, and the input terminal 701 of the drive voltage detection circuit 70, and the ground, and the voltage vd2 is the drain 362 of the transistor 36.
And the drive voltage generated between the intersection of the primary electrode 402 of the piezoelectric transformer and the ground. When the transistor 35 is turned on, as shown in FIG.
-An energy storage circuit is formed by the coil 33 and the transistor 35. In this case, since the voltage between the terminals of the coil 33 is almost Vcc, as shown in FIG. 3, a current il1 having a slope of Vcc / L33 (L33: inductance of the coil 33) flows through the coil 33, and the drive voltage vd1 is It is zero. In this case, the current iq1 flowing through the transistor 35 is the same as the current flowing through the coil 33 and the piezoelectric transformer 40.
Are synthesized from the resonance current flowing out of the primary electrode 401. Similarly, when the transistor 36 is on, the voltage between the terminals of the coil 34 is substantially Vcc,
, A current il1 having a slope of Vcc / L34 (L34: inductance of the coil 34) flows, and the drive voltage vd2 is zero. In this case, the current iq2 flowing through the transistor 36 is the same as the current flowing through the coil 34 and the piezoelectric transformer 4
The result is a composite of the resonance current flowing out of the 0 primary electrode 402.

When the transistor 35 is off, whether a resonance circuit is formed by the coil 33, the piezoelectric transformer 40, the transistor 36 and the diode 31, as shown in FIG.
As shown in FIG. 9, the transistor 36 and the piezoelectric transformer 4
0, the coil 33, the parasitic diode 213, and the power supply 10 form a resonance circuit. In this case, as shown in FIG. 3, the inductance of the coil 33, the primary electrode 401 of the piezoelectric transformer 40, and the piezoelectric transformer 401
Resonant current il1 with the equivalent input capacitance during the time 02 as a time constant
Flows, and at the intersection of the drain 352 of the transistor 35 and the primary electrode 401, a drive voltage vd1 having an amplitude about twice the power supply voltage Vcc is generated. In this case, the transistor 35 is off, and the current iq1 is zero. Similarly, when the transistor 36 is off, the coil 34 has a resonance current il2 having a time constant of the inductance of the coil 34 and the equivalent input capacitance between the primary electrode 401 of the piezoelectric transformer 40 and the primary electrode 401 of the piezoelectric transformer 40. As a result, a drive voltage vd2 having an amplitude about twice the power supply voltage Vcc is generated at the drain 362 and the primary electrode 402 of the transistor 36. In this case, since the transistor 36 is off, the current iq2 is zero.

Next, FIG. 4 shows a timing chart when the on-time of the transistor 21 and the transistor 22 is shorter than the off-time. When the transistor 21 is off and the transistor 35 is on, as shown in FIG.
7, or as shown in FIG. 7, the transistor 35, the coil 33, the parasitic diode 213 and the power supply 1
0 forms a circuit. In this case, since the forward voltage of the diode 31 can be regarded as sufficiently small, the voltage between the terminals of the coil 33 is almost zero, and as shown in FIG.
The current il1 flowing through the coil 33 is constant or zero (in FIG. 4, the case is shown as zero), and the drive voltage vd1 is zero.
In this case, the current iq1 flowing through the transistor 35 is determined by the current flowing through the coil 33 and the primary electrode 4 of the piezoelectric transformer 40.
01 is obtained by synthesizing the resonance current flowing out of the circuit. When the transistor 21 is on and the transistor 35 is on, an energy storage circuit as shown in FIG. 5 is formed.
In this case, since the voltage between the terminals of the coil 33 is almost Vcc, the inclination of the coil 33 is Vcc /
A current il1 serving as L33 (L33: inductance of the coil 33) flows, and the drive voltage vd1 is zero. Also, in this case, the current iq1 flowing through the transistor 35 depends on the current flowing through the coil 33 and the primary electrode 40 of the piezoelectric transformer 40.
1 is obtained by synthesizing the resonance current flowing out of 1. Similarly, when the transistor 22 is off and the transistor 36 is on, the forward voltage of the diode 32 can be regarded as sufficiently small, so that the voltage between the terminals of the coil 34 is almost zero, and the current il2 flowing through the coil 34 is constant. Or zero (in FIG. 4, the case of zero is shown), and the drive voltage vd2 is zero. In this case, the current iq2 flowing through the transistor 36 is the same as the current flowing through the coil 34 and the piezoelectric transformer 4
The result is a composite of the resonance current flowing out of the 0 primary electrode 402. Transistor 22 is on and transistor 3
6 is on, the voltage between the terminals of the coil 34 is almost Vcc.
Therefore, the inclination of the coil 34 is Vcc / L34 (L
34: current il2 which is the inductance of the coil 34)
Flows, and the drive voltage vd2 is zero. In this case, the current iq2 flowing through the transistor 36 is a combination of the current flowing through the coil 34 and the resonance current flowing out of the primary electrode 402 of the piezoelectric transformer 40.

When the transistor 35 is off, a resonance circuit as shown in FIG. 8 or 9 is formed. At this time, the coil 33 includes the inductance of the coil 33, the primary electrode 401 of the piezoelectric transformer 40, and the primary electrode 4 of the piezoelectric transformer 40.
Resonant current il1 with the equivalent input capacitance during the time 02 as a time constant
Flows to the drain 352 of the transistor 35 and the primary electrode 401 of the piezoelectric transformer 40 by about 2 Vcc ×
(ON time of transistor 21) / (transistor 35
A drive voltage vd1 having an amplitude of (ON time of the drive signal) is generated.
In this case, the transistor 35 is off, and the current iq1 is zero. Similarly, when the transistor 36 is turned off, the coil 34 has a resonance current il2 whose time constant is the inductance of the coil 34 and the equivalent input capacitance between the primary electrode 401 of the piezoelectric transformer 40 and the primary electrode 402 of the piezoelectric transformer 40. Flows, and the drain 362 of the transistor 36
And the primary electrode 402 of the piezoelectric transformer 40 has approximately 2
A drive voltage vd2 having an amplitude of Vcc × (on time of transistor 22) / (on time of transistor 36) is generated. In this case, the transistor 36 is off, and the current iq2 is zero.

The configuration of the frequency control section 60 will be described in detail. The input terminal 611 of the current-voltage conversion circuit 61 is connected to the load 5
0 is connected to the low voltage terminal 502. Current-voltage conversion circuit 6
The first output terminal 612 is connected to the input terminal 621 of the voltage controlled oscillation circuit 62. Output terminal 6 of voltage controlled oscillation circuit 62
22 is connected to the input terminal 631 of the drive control circuit 63.
The output terminal 632 of the drive control circuit 63 is connected to the input terminal 251 of the input power control circuit 25 and the buffer 64. The output terminal 633 of the drive control circuit 63 is connected to the input terminal 252 of the input power control circuit 25 and the buffer 65.

The operation of the frequency control section 60 will be described. The current-voltage conversion circuit 61 converts the voltage of the AC load current iol input to the terminal 611, rectifies and smoothes the output, and outputs it to the voltage-controlled oscillation circuit 62. The voltage control oscillation circuit 62 supplies a pulse voltage having a frequency corresponding to the input voltage from the input terminal 621 to the buffer 6 via the drive control circuit 63.
4 and the buffer 65 and the input power control circuit 25. The buffer 64 and the buffer 65 are
The pulse voltage output from the output terminal 632 and the output terminal 633 of the third
Amplify to the voltage that can be driven. The frequency controller 60 controls the frequency of the pulse voltage output to the gate 351 of the transistor 35 and the gate 361 of the transistor 36 in order to keep the load current iol flowing out of the low voltage terminal 502 of the load 50 constant.

By the switching operation of the transistor 35 and the transistor 36 on and off, an approximate sine wave voltage vpt of the frequency f is applied between the primary electrode 401 of the piezoelectric transformer 40 and the primary electrode 402 of the piezoelectric transformer 40. appear. In this case, an output voltage vo of Av × vpt (Av: step-up ratio of the piezoelectric transformer at the frequency f) is generated at the secondary electrode 403 of the piezoelectric transformer 40, and the voltage of the load 50 − Current characteristics (load 50
(A relationship between the voltage vo between the high voltage terminal 501 and the low voltage terminal 502 and the tube current iol) flows out. The current-voltage conversion circuit 61 converts the load current iol flowing out of the low-voltage terminal 502 of the load 50 into a voltage using a resistor or the like, rectifies and smoothes it. The voltage control oscillation circuit 62 controls the drive control circuit 6 so that the voltage proportional to the load current iol input from the current-voltage conversion circuit 61 is always constant.
3, the frequency of the pulse voltage to be output is changed. The drive control circuit 63 generates a pulse voltage having a frequency f different in phase from each other by 180 degrees based on the pulse voltage output from the voltage control oscillation circuit 62, and outputs the gate voltage of the transistor 35 via a buffer 64 and a buffer 65, respectively. 351 and the gate 361 of the transistor 36. Due to the above operation of the frequency control unit 60, a voltage vo such that a preset load current value iol flows is obtained regardless of the impedance variation and the temperature characteristic of the load 50.
At the secondary electrode 403. The drive control circuit 63
Outputs a pulse voltage to the input terminals 251 and 252 of the input power control circuit 25 at the same time as outputting the pulse voltage to the buffers 64 and 65.

The configuration and operation of the drive voltage detection circuit 70 will be described. The input terminal 701 of the drive voltage detection circuit 70 is connected to the drain 352 of the transistor 35 and the piezoelectric transformer 40.
To the intersection of the primary electrodes 401. Further, the output terminal 702 of the drive voltage detection circuit 70 is connected to the input terminal 253 of the input power control circuit 25. The drive voltage detection circuit 70
The driving voltage generated at the drain 352 of the transistor 35 is divided, the amplitude of the waveform is detected and smoothed, and output to the input terminal 253 of the input power control circuit 25.

By the operation according to the above configuration, as shown in the timing charts of FIGS.
When 5 is off, that is, when a resonance circuit is formed by the inductance of the coil 33 and the equivalent capacitance between the primary electrodes of the piezoelectric transformer 40, the transistor 21 is always off, and the transistor 21 is turned off from the power supply 10 via the coil 33. Next electrode 40
The current path towards 1 is interrupted. Similarly, when the transistor 36 is off, that is, when a resonance circuit is formed by the inductance of the coil 34 and the equivalent capacitance between the primary electrodes of the piezoelectric transformer 40, the transistor 22 is always off and the power supply 10 disconnects the coil 34. The current path toward the primary electrode 402 through the connection is cut off. With this operation, the piezoelectric transformer drive circuit of the present invention can prevent an excessive current from flowing from the power supply 10 to the drive voltage generator 30 as seen in a conventional piezoelectric transformer drive circuit.

Embodiment 2 The structure of the second embodiment of the present invention will be described. As shown in FIG. 6, the drive circuit of the second embodiment includes an intersection between the primary electrode 401 of the piezoelectric transformer 40 and the drain 352 of the transistor 35, and a connection between the primary electrode 402 of the piezoelectric transformer 40 and the drain 362 of the transistor 36. The input terminal 701 of the drive voltage detection circuit 70 and the input terminal 711 of the drive voltage detection circuit 71 are connected to the intersections. Further, the output terminal 702 of the drive voltage detection circuit 70 and the drive voltage detection circuit 7
1 is connected to the input terminal 801 of the comparison circuit 80.
And 802. Output terminal 803 of comparison circuit 80
To the input terminal 253 of the input power control circuit 25.
Other configurations are the same as those of the first embodiment shown in FIG. In this embodiment, a transistor can be, for example, a field-effect transistor or a bipolar transistor, and a diode can be, for example, a Schottky barrier diode, and a piezoelectric transformer is, for example, a Rosen secondary type single plate type. A Rosen secondary type laminated type, Rosen tertiary type single plate type, Rosen tertiary type laminated type and the like can be used, and the load can be a cold cathode tube or the like. As for the load, a device for charging the toner of the copying machine, a device for flashing the camera, and the like can be used.

Next, the operation of the second embodiment of the present invention will be described. In the drive circuit of the second embodiment, as shown in FIG.
The drive voltage vd1 generated at the primary electrode 401 of 0 is divided to detect and smooth the amplitude, and at the same time, the drive voltage detection circuit 71
In step (1), the drive voltage vd2 generated on the primary electrode 402 of the piezoelectric transformer 40 is divided to detect the amplitude and smooth the amplitude. The driving circuit of the piezoelectric transformer according to the present invention includes a driving voltage detecting circuit 7.
0 and the voltage output from the drive voltage detection circuit 71 are compared by a comparison circuit 80, and the higher voltage is input to the input power control circuit 253. The operations of the input power controller 20, the drive voltage generator 30, and the frequency controller 60 are the same as those of the drive circuit shown in FIG. With the configuration shown in FIG.
3 and the amplitude of the drive voltage vd1 generated on the primary electrode 401 of the piezoelectric transformer 40 due to variations in the inductance of the coil 34 and the like.
2 have different amplitudes of the driving voltage vd2,
The transistors 21 and 22 are driven such that the amplitudes of the drive voltages vd1 and vd2 are equal to or less than a value set arbitrarily.
The on / off time ratio can be controlled.
Overcurrent to the drive voltage generator 30 can be prevented.

Third Embodiment Next, the configuration of a third embodiment of the present invention will be described with reference to FIG. The driving circuit of the piezoelectric transformer shown in FIG. 11 includes an input power control unit 202 including the transistor 21 / buffer 23 and the input power control circuit 25, a driving voltage generation unit 302 including the diode 31, the coil 33, and the transistor 35; A frequency control unit 602 including a voltage conversion circuit 61, a voltage control oscillation circuit 62, a drive control circuit 63, and a buffer 64; a drive voltage detection circuit 70;
It comprises a piezoelectric transformer 40 and a load 50 as a load. In this embodiment, a transistor can be, for example, a field-effect transistor or a bipolar transistor, and a diode can be, for example, a Schottky barrier diode, and a piezoelectric transformer is, for example, a Rosen secondary type single plate type. Rosen secondary type laminated type
A Rosen tertiary single plate type, a Rosen tertiary laminate type or the like can be used, and the load can be a cold cathode tube or the like. As for the load, a device for charging the toner of the copying machine, a device for flashing the camera, and the like can be used.

The configuration of the input power control section 202 will be described in detail. The source 214 of the transistor 21 is connected to the power supply 10,
The drain 212 is connected to the cathode 312 of the diode 31 and one end 331 of the coil 33, and the gate 211 is connected to the buffer 2
3 output. The diode 213 is a parasitic diode of the transistor 21. The input terminal 251 of the input power control circuit 25 is connected to the output terminal 632 of the drive control circuit 63.
Then, the input terminal 253 is connected to the output terminal 702 of the drive voltage detection circuit 70. Output terminal 2 of input power control circuit 25
54 is connected to the buffer 23.

The operation of the input power control section 202 will be described. The input power control circuit 25 adjusts the high level of the pulse voltage output from the output terminal 632 of the drive control circuit 63 so that the voltage value output from the output terminal 702 of the drive voltage detection circuit 70 always becomes a fixed value or less. The low-level time ratio is converted and output to the buffer 23. The buffer 23 amplifies the pulse voltage output from the output terminal 254 of the input power control circuit 25 to a voltage at which the transistor 21 can be driven.

The configuration of the drive voltage generator 302 will be described in detail. One end 331 of the coil 33 is connected to the cathode 312 of the diode 31 and the drain 212 of the transistor 21. The anode 311 of the diode 31 is connected to the ground. The other end 332 of the coil 33 is connected to the transistor 35
Drain 352 and the primary electrode 401 of the piezoelectric transformer 40
And the input terminal 701 of the drive voltage detection circuit 70. The source 354 of the transistor 35 is connected to the ground, and the gate 351 is connected to the output of the buffer 64. The diode 353 is a parasitic diode of the transistor 35.

The configuration of the piezoelectric transformer 40 and the load 50 will be described. The primary electrode 402 of the piezoelectric transformer 40 is connected to the ground. Load the secondary electrode 403 of the piezoelectric transformer 40 with the load 5
0 high voltage terminal 501.

The configuration of the frequency control section 602 will be described in detail. The input terminal 611 of the current-voltage conversion circuit 61 is connected to the load 5
0 is connected to the low voltage terminal 502. Current-voltage conversion circuit 6
The first output terminal 612 is connected to the input terminal 621 of the voltage controlled oscillation circuit 62. Output terminal 6 of voltage controlled oscillation circuit 62
22 is connected to the input terminal 631 of the drive control circuit 63.
The output terminal 632 of the drive control circuit 63 is connected to the input terminal 251 of the input power control circuit 25 and the buffer 64.

The operation of the frequency control section 602 will be described.
The current-voltage conversion circuit 61 converts the AC load current iol input to the input terminal 611 into a voltage, rectifies and smoothes the output, and outputs the rectified current to the voltage control oscillation circuit 62. The voltage control oscillation circuit 62 outputs a pulse voltage having a frequency corresponding to the input voltage from the terminal 621 to the buffer 64 and the input power control circuit 25 via the drive control circuit 63. The buffer 64
The pulse voltage output from the output terminal 632 of the drive control circuit 63 is amplified to a voltage at which the transistor 35 can be driven.

The configuration of the drive voltage detection circuit 70 will be described in detail. The input terminal 701 of the drive voltage detection circuit 70 is connected to the intersection of the drain 352 of the transistor 35 and the primary electrode 401 of the piezoelectric transformer 40. Further, the output terminal 702 of the drive voltage detection circuit 70 is connected to the input terminal 253 of the input power control circuit 25.

The operation of the drive voltage detection circuit 70 will be described. The drive voltage detection circuit 70 divides the drive voltage generated at the drain of the transistor 35, detects the amplitude of the waveform, smoothes the amplitude, and outputs it to the input power control circuit 25.

Next, the operation of the third embodiment of the present invention will be described. In the driving circuit of the piezoelectric transformer shown in FIG.
FIG. 12 shows a timing chart when the on-time and off-time of the transistor 21 are equal, and FIG. 13 shows a timing chart when the on-time of the transistor 21 is shorter than the off-time. As shown in FIGS. 12 and 13,
Switching operation of the transistor 21 and the transistor 35 on and off, and the primary electrode 401 of the piezoelectric transformer 40
Is generated in the same manner as the drive circuit of the first embodiment shown in FIG. In the driving circuit of the third embodiment, the voltage waveform vpt input between the primary electrode 401 of the piezoelectric transformer 40 and the primary electrode 402 of the piezoelectric transformer 40 is an approximate half-wave sine wave. Of 1
The harmonic component increases as compared with the drive circuit of FIG. 1 in which an approximate sinusoidal voltage is generated between the next electrode 401 and the primary electrode 402 of the piezoelectric transformer 40. However, the drive circuit of the piezoelectric transformer of the present invention can prevent the overcurrent generated in the drive circuit of the conventional piezoelectric transformer, and can be compared with the drive circuit of the piezoelectric transformer shown in FIG.・ Buffer 24 ・ Buffer 65
In addition, the diode 32 can be eliminated, and the drive circuit of the piezoelectric transformer can be reduced in size and cost.

Embodiment 4 Next, a fourth embodiment of the present invention will be described. The configuration of the piezoelectric transformer drive circuit of the fourth embodiment is equal to the configuration of the first embodiment shown in FIG. 1 or the second embodiment shown in FIG. The operation of the fourth embodiment will be described. In the driving circuit of the piezoelectric transformer shown in FIG. 1 or FIG.
When the on-time and the off-time of 1 and 22 are equal, the inductance of the coil 33 and the coil 34 is adjusted, and the driving voltage vd1 and the driving voltage generated on the primary electrode 401 of the piezoelectric transformer 40 and the primary electrode 402 of the piezoelectric transformer 40 are adjusted. The amplitude of the voltage vd2 is 1.5 times or more of the power supply voltage Vcc and
6 times or less. The driving circuit of the piezoelectric transformer of the present invention
By setting the amplitudes of the drive voltage vd1 and the drive voltage vd2 to 1.5 times or more and 1.6 times or less of the power supply voltage Vcc, the timing at which the drive voltages vd1 and vd2 become zero, and the turning-on of the transistor 35 and the transistor 36 And the timing of switching off, the DC energy supplied from the power supply 10 is converted to AC power most efficiently to drive the piezoelectric transformer 40 and reduce the power consumption of the drive circuit.

Embodiment 5 Next, a fifth embodiment of the present invention will be described. The configuration of the piezoelectric transformer drive circuit of the fifth embodiment is equal to the configuration of the third embodiment shown in FIG. The operation of the fifth embodiment will be described. In the driving circuit of the piezoelectric transformer shown in FIG. 11, when the ON time and the OFF time of the transistor 21 are equal, the inductance of the coil 33 is adjusted and
The amplitude of the drive voltage vd1 generated at the primary electrode 401 of 0 is set to 1.5 times or more and 1.6 times or less of the power supply voltage Vcc. The driving circuit of the piezoelectric transformer of the present invention has a driving voltage vd
1 is 1.5 times or more the power supply voltage Vcc and 1.6
By making the drive voltage vd1 zero or less, the timing at which the drive voltage vd1 becomes zero coincides with the timing at which the transistors 35 and 36 are turned on and off, and the power supply 1
The DC energy supplied from 0 is most efficiently converted to AC energy to drive the piezoelectric transformer 40 to reduce the power consumption of the drive circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a driving circuit for a piezoelectric transformer according to a first embodiment of the present invention.

FIG. 2A is a diagram showing energy efficiency of a piezoelectric transformer with respect to a frequency of a voltage applied to the piezoelectric transformer in a general piezoelectric transformer. FIG. 6B is a diagram of a boost ratio of the piezoelectric transformer with respect to a frequency of a voltage applied to the piezoelectric transformer in a general piezoelectric transformer. C In a general piezoelectric transformer, it is a diagram of the amplitude of the driving voltage of the piezoelectric transformer with respect to the frequency of the voltage applied to the piezoelectric transformer. D is a diagram of a boost ratio of a piezoelectric transformer with respect to a frequency of a voltage applied to the piezoelectric transformer at three kinds of impedance values in a general piezoelectric transformer.

FIG. 3 shows a transistor 21 and a transistor 22 in the driving circuit of the piezoelectric transformer according to the first embodiment of the present invention.
A timing chart in the case where the on-time and the off-time of the transistor 35 and the transistor 36 are equal, and the current i before and after the switching of the transistor;
It is a figure which shows the current amplitude value of l1, current il2, current iq1, and current iq2, and the voltage amplitude value of voltage vd1 and voltage vd2.

FIG. 4 shows a transistor 21 and a transistor 22 in the driving circuit for the piezoelectric transformer according to the first embodiment of the present invention.
The time during which either of them is turned on is determined by the transistor 35
A timing chart in a case where the time is shorter than the time when the transistor 36 is turned on or off, and the current amplitude value and the voltage vd1 of the current il1, the current il2, the current iq1, and the current iq2 before and after the switching of the transistor. FIG. 6 is a diagram illustrating a voltage amplitude value of a voltage vd2.

FIG. 5 is a circuit diagram of the drive circuit for the piezoelectric transformer according to the first embodiment of the present invention, which is formed by the power supply 10, the transistor 21, the coil 33, and the transistor 35 formed when the transistor 21 is on and the transistor 35 is on. FIG. 2 is a circuit diagram of an energy storage circuit to be used.

FIG. 6 shows a coil 33 and a transistor 3 when the transistor 21 is off and the transistor 35 is on in the piezoelectric transformer driving circuit according to the first embodiment of the present invention.
5 is a circuit diagram in which a circuit is formed by 5 and a diode 31. FIG.

FIG. 7 is a diagram illustrating a transistor 35 and a coil 3 when the transistor 21 is off and the transistor 35 is on in the driving circuit of the piezoelectric transformer according to the first embodiment of the present invention.
3 is a circuit diagram in which a circuit is formed by the parasitic diode 213 and the power supply 10.

FIG. 8 is a circuit diagram in which a resonance circuit is formed by the coil 33, the piezoelectric transformer 40, the transistor 36, and the diode 31 when the transistor 35 is off in the piezoelectric transformer drive circuit according to the first embodiment of the present invention. .

9 shows a driving circuit of the piezoelectric transformer according to the first embodiment of the present invention, in which the transistor 36, the piezoelectric transformer 40, the coil 33, the parasitic diode 213, and the power supply 10 form a resonance circuit when the transistor 35 is off. It is a circuit diagram.

FIG. 10 is a circuit diagram of a driving circuit for a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 11 is a circuit diagram of a piezoelectric transformer drive circuit according to a third embodiment and a fifth embodiment of the present invention.

FIG. 12 is a timing chart in the case where the on-time and the off-time of the transistor 21 and the transistor 35 are equal in the driving circuit of the piezoelectric transformer according to the third embodiment of the present invention, and the current before and after the switching of the transistors. It is a figure which shows the current amplitude value of il1 * current iq1, and the voltage amplitude value of voltage vd1.

FIG. 13 is a timing chart in the case where the on time of the transistor 21 is shorter than the off time in the driving circuit for the piezoelectric transformer according to the third embodiment of the present invention;
It is a figure which shows the current amplitude value of the current il1 and the current iq1, and the voltage amplitude value of the voltage vd1 before and after the switch switching of the transistor 21 and the transistor 35.

FIG. 14 is a circuit diagram of a conventional piezoelectric transformer drive circuit.

FIG. 15 shows a transistor 13 in a conventional piezoelectric transformer drive circuit when the transistor 121 is always on.
4. Current il1, current il2, current iq1, and current iq before and after switching of the transistor 135
FIG. 3 is a diagram showing a current amplitude value of a voltage 2 and voltage amplitude values of a voltage vd1 and a voltage vd2.

FIG. 16 shows a conventional piezoelectric transformer drive circuit.
A timing chart in the case where the time during which the transistor 121 is turned on is shorter than the time during which the transistor 135 and the transistor 136 are turned on or off, and the current i before and after the switching of the transistor.
FIG. 9 is a diagram showing current amplitude values of l1, current il2, current iq1, and current iq2 and voltage amplitude values of voltages vd1 and vd2 in comparison with the piezoelectric transformer drive circuits according to the first to fifth embodiments of the present invention.

[Explanation of symbols]

 Reference Signs List 10 power supply 20 input power control unit 30 drive voltage generation unit 40 piezoelectric transformer 50 load 60 frequency control unit 70 drive voltage detection circuit 80 comparison circuit

Continued on the front page F term (reference) 2H093 NA06 NC05 NC58 ND42 ND54 3K072 AA01 AA19 BA03 BA05 BC07 EB05 EB07 GA02 GB14 GC04 HA06 HA10 HB03 5H007 BB03 CA02 CB06 CB09 CC12 CC32 DA03 DB03 DC02 DC05 5H730 AA14 FD01 BB31

Claims (10)

[Claims] An input power control unit for inputting power from a DC power supply, a drive voltage generation unit for inputting power from the input power control unit and outputting an AC voltage, and a frequency control unit for controlling a frequency of the AC voltage. A driving voltage detecting circuit for detecting an AC voltage generated by the driving voltage generating unit, a piezoelectric transformer for inputting an AC voltage from a primary electrode and outputting an AC voltage from a secondary electrode using a piezoelectric effect, A drive circuit for a piezoelectric transformer, comprising: a load driven by electric power transformed by the transformer. 2. The piezoelectric transformer drive circuit according to claim 1, wherein the input power control unit includes a transistor, a buffer, and an input power control circuit. 3. The driving circuit for a piezoelectric transformer according to claim 1, wherein the driving voltage generator includes a diode, a coil, and a transistor. 4. The piezoelectric transformer according to claim 1, wherein the frequency control unit includes a current-voltage conversion circuit, a voltage control oscillation circuit, a drive control circuit, and a buffer. Drive circuit. 5. The input power control section, wherein two transistors and one buffer are provided for each of the transistors, and each of the buffers is connected to an input power control circuit. A driving circuit for a piezoelectric transformer according to claim 4. 6. The driving voltage generating unit according to claim 1, wherein two diodes and one diode are provided for each of said diodes, and one transistor is provided for each of said coils. A driving circuit for driving the piezoelectric transformer according to claim 5. 7. The frequency control unit according to claim 1, wherein the current-voltage conversion circuit, the voltage control oscillation circuit, the drive control circuit, and two buffers are connected to the drive control circuit.
A driving circuit for a piezoelectric transformer according to claim 6. 8. The driving circuit for a piezoelectric transformer according to claim 1, wherein in the driving voltage generating section, the inductances of the two coils are made substantially equal to each other. 9. An input power control circuit installed in the input power control unit outputs a signal obtained by changing a time ratio between a high level voltage portion and a low level voltage portion of the pulse voltage rectangular wave input from the frequency control unit. The driving circuit for a piezoelectric transformer according to any one of claims 1 to 8, wherein: 10. The time when one of the two transistors provided in the input voltage control unit is turned on is shorter than the time when two transistors provided in the drive voltage generation unit are turned on or off. The driving circuit for a piezoelectric transformer according to claim 1, wherein the driving frequency is set.