JPH10239657A - Driving circuit for piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving circuit for piezoelectric transformer which is suitable for input of an input voltage in a wide range. SOLUTION: An input terminal 12, a piezoelectric transformer 80, a piezoelectric transformer driving circuit 70, and a switch Q3 are provided. The transformer driving circuit 70 is provided with auto-transformers 71 and 75, and primary terminals of auto-transformers 71 and 75 are connected to the switch Q3 together, and switches Q1 and Q2 are connected to middle terminals respectively. A driving waveform ϕ3 of the switch Q3 is synchronized with driving waveforms ϕ1 and ϕ2 of switches Q1 and Q2. The frequency of the driving waveform ϕ3 is twice as high as frequencies of driving waveforms ϕ1 and ϕ2 . The on-duty ratio of the driving waveform ϕ3 is so controlled that it is lower for a higher input voltage Vin and is higher for a lower input voltage Vin, and the power applied to auto-transformers 71 and 75 is fixed or is lower than a prescribed power independently of the value of the input voltage Vin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driving circuit for a piezoelectric transformer, and more particularly to a driving circuit for a piezoelectric transformer in a power conversion circuit using the piezoelectric transformer.

[0002]

2. Description of the Related Art A piezoelectric transformer is an element used in a power conversion circuit. In this case, a driving circuit for applying a sine wave voltage between the primary terminals of the piezoelectric transformer is required.

[0003] Such a driving circuit is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-275553.

[0004] As shown in FIG. 7, in this drive circuit 300, power specified from output power is input to auto transformers 71 and 75 connected to primary terminals 81 and 82 of a piezoelectric transformer 80. Electric power is output to the load 90 through the piezoelectric transformer 80.

[0005]

A power conversion circuit using a piezoelectric transformer is expected to be applied to an inverter circuit for lighting a cold cathode fluorescent lamp (CCFL).

The inventor of the present invention has conducted intensive studies to apply a piezoelectric transformer to an inverter circuit for lighting a CCFL, and as a result, has found that the drive circuit 300 has the following problems.

That is, since the power supply of the inverter circuit is a battery or an AC adapter, the input voltage Vin of the inverter circuit fluctuates due to the consumption of the battery, switching from the battery to the AC adapter, and the like.

Recently, a lithium ion rechargeable battery having a large storage capacity has been often used as a battery for a power supply. In the case of this battery, there is a difference of about twice between the maximum value and the minimum value of the output voltage. When an AC adapter is connected, the voltage is higher than the maximum value. That is, the range of the input voltage Vin of the inverter circuit has been widened.

In the above prior art, the input voltage Vin
Fluctuates, the primary terminals 81, 8 of the piezoelectric transformer 80
The power input to the autotransformers 71 and 75 connected to the power supply 2 changes. This input power is proportional to the input voltage Vin of the inverter circuit.

Therefore, a transformer connected to the primary terminal of the piezoelectric transformer was designed as follows.

First, when the input voltage Vin of the inverter circuit is at the minimum value, specified power is supplied to the auto transformers 71 and 75.
The autotransformers 71 and 75 are designed so that they can be input to the. Next, a core whose size does not cause magnetic saturation in the cores of the autotransformers 71 and 75 when the input voltage Vin of the inverter circuit has the maximum value is selected.

By designing in this manner, the transformer 7
The core size of 1, 75 is the size calculated from the output power multiplied by the ratio between the maximum value and the minimum value of the input voltage Vin of the inverter circuit. Therefore, the core becomes a large size for the output power of the inverter circuit. In this example, the size is twice or more the size calculated from the output power. As a result, the size of the inverter circuit is large and the price is high.

Accordingly, it is an object of the present invention to provide a driving circuit for a piezoelectric transformer which is suitable when a wide range of input voltage is input.

[0014]

According to the first aspect, an input terminal to which a power supply is connected, a driving means capable of applying an alternating current of a predetermined frequency to the primary side of the piezoelectric transformer, the input terminal and the drive Control means inserted between the input means and a control means capable of controlling an on-duty ratio of a voltage applied to the drive means in accordance with a voltage from the power supply input to the input terminal;
And a driving circuit for driving the piezoelectric transformer.

According to the second aspect, the control means reduces the on-duty ratio of the voltage applied to the driving means as the voltage from the power supply input to the input terminal increases. 2. The piezoelectric device according to claim 1, wherein the control unit is a control unit that can control the on-duty ratio of the voltage applied to the driving unit to increase as the voltage from the power supply input to the input terminal decreases. A transformer driving circuit is provided.

According to the third aspect, an input terminal to which a power supply is connected, a driving means capable of applying an alternating current having a predetermined frequency to the primary side of the piezoelectric transformer, and a driving means between the input terminal and the driving means. And a control unit that is capable of controlling power applied to the driving unit in accordance with a voltage from the power supply input to the input terminal. .

According to the fourth aspect, the control means determines that the power applied to the drive means is equal to or less than a predetermined power or a constant power regardless of the voltage from the power supply input to the input terminal. A driving circuit for a piezoelectric transformer according to claim 3, wherein the driving circuit is a control means that can be controlled as follows.

Further, according to claim 5, an input terminal to which a power supply is connected, a driving means capable of applying an alternating current of a predetermined frequency to the primary side of the piezoelectric transformer, and a driving means between the input terminal and the driving means. And a first switching means inserted in series with the piezoelectric transformer.

According to a sixth aspect of the present invention, there is further provided a second control means capable of controlling an on-duty ratio of the first switching means in accordance with a voltage from the power supply input to the input terminal. A driving circuit for a piezoelectric transformer according to claim 5 is provided.

According to claim 7, the second control means reduces the on-duty ratio of the first switching means as the voltage from the power supply input to the input terminal increases. 7. The control means according to claim 6, wherein said control means is controllable to increase the on-duty ratio of said first switching means as the voltage from said power supply input to said input terminal decreases. A driving circuit for a piezoelectric transformer is provided.

Further, according to the present invention, irrespective of the voltage from the power supply input to the input terminal, the power applied to the driving means is equal to or less than a predetermined power or a constant power. The driving circuit for a piezoelectric transformer according to claim 5, further comprising third control means capable of controlling switching timing of the first switching means.

According to the ninth aspect, a first control signal of a first frequency is generated based on a signal from an input terminal to which a power supply is connected and a load driven by a piezoelectric transformer, and A second control signal having a second frequency of a frequency that is an integer multiple of 2 or more of the first frequency based on a signal from a load driven by a transformer and a voltage from the power supply input to the input terminal; A fourth control means for generating the second control signal having a predetermined on-duty; and n times the first frequency being applied to a primary side of the piezoelectric transformer based on the first control signal. Or 1 / n
Driving means capable of applying an alternating current of a third frequency of a frequency twice (n is an integer of 1 or more), and first switching means inserted in series between the input terminal and the driving means And the first switching means, which is switched by the second control signal at a frequency of the second frequency and an integer multiple of 2 or more of the third frequency. A driving circuit for a piezoelectric transformer is provided.

In this case, preferably, the second frequency is twice the first frequency, n is 1, and the second frequency is twice the third frequency.

According to a tenth aspect, the fourth control means reduces the on-duty ratio as the voltage from the power supply input to the input terminal increases, and the fourth control means inputs the on-duty ratio to the input terminal. 10. A driving circuit for driving a piezoelectric transformer according to claim 9, wherein the control means increases the on-duty ratio as the voltage from the power supply decreases.

According to the eleventh aspect, a first circuit for generating a first signal of a first frequency based on an input terminal connected to a power supply and a signal from a load driven by a piezoelectric transformer. And a second frequency of n times or 1 / n times (n is an integer of 1 or more) of the first frequency based on the first signal and the voltage input to the input terminal. A second circuit for generating a second signal having a predetermined on-duty ratio, which is a second signal having a frequency, and two or more of the second frequency based on the first or second signal; A third circuit that generates a third signal having a third frequency that is an integral multiple of the third frequency; and applying the third frequency alternating current to the primary side of the piezoelectric transformer based on the third signal. A drive unit capable of applying the voltage, and an input terminal connected in series between the input terminal and the drive unit. A driving circuit for a piezoelectric transformer, comprising: a first switching unit configured to switch at the second frequency in accordance with the second signal. You.

In this case, preferably, n is 1 and the third frequency is 1/2 of the second frequency.

According to the twelfth aspect, the second circuit reduces the on-duty ratio as the voltage from the power supply input to the input terminal increases,
12. The piezoelectric transformer drive circuit according to claim 11, wherein the circuit is configured to increase the on-duty ratio as the voltage from the power supply input to the input terminal decreases.

According to a thirteenth aspect of the present invention, there is provided a piezoelectric transformer driving circuit according to any one of the first to twelfth aspects, wherein the driving means includes an inductance element. You.

According to a fourteenth aspect of the present invention, there is provided the piezoelectric transformer driving circuit according to any one of the first to thirteenth aspects, wherein the driving means includes an electromagnetic transformer. You.

According to a fifteenth aspect, the electromagnetic transformer has a core.
A drive circuit for the described piezoelectric transformer is provided.

According to claim 16, the driving means is inserted in series between the control means or the first switching means and the primary winding of the inductance element or the electromagnetic transformer. A second switching means, and a fifth switching means for switching the second switching means at the predetermined frequency or the third frequency.
The piezoelectric transformer driving circuit according to any one of claims 13 to 15, further comprising:

According to the seventeenth aspect, the driving means is connected in series between the inductance element or the electromagnetic transformer, the first switching means, and the primary winding of the inductance element or the electromagnetic transformer. Further comprising inserted second switching means, and fifth control means for switching the second switching means at the predetermined frequency or the third frequency, wherein the second or third control means However, when the first switching means is switched to the predetermined frequency or the third frequency
The piezoelectric transformer drive circuit according to any one of claims 6 to 8, wherein the control means is a control means for switching at a fourth frequency which is an integer multiple of the frequency.

In this case, preferably, the fourth frequency is twice the predetermined frequency or the third frequency.

According to the eighteenth aspect, a difference is provided between the switching phase of the first switching means and the switching phase of the second switching means. 17. A driving device for a piezoelectric transformer according to item 17.

According to the nineteenth aspect, the driving means includes a first inductance element or a first electromagnetic transformer, the control means or the first switching means, and the first inductance element or the first switching element. The third electromagnetic transformer inserted in series with the primary winding of the first electromagnetic transformer
Switching means, a second inductance element or a second electromagnetic transformer, the control means or the first
Switching means, and fourth switching means inserted in series between the second inductance element or the primary winding of the second electromagnetic transformer, and the driving circuit of the piezoelectric transformer comprises: The third and fourth switching means are switched at the predetermined frequency or the third frequency by changing the phase by 180 degrees between the third switching means and the fourth switching means. The piezoelectric transformer driving circuit according to any one of claims 1 to 12, further comprising a control unit (6).

According to a twentieth aspect, the driving means includes a first inductance element or a first electromagnetic transformer, the first switching means, the first inductance element or the first electromagnetic element. A third switching means inserted in series between the primary winding of the transformer, a second inductance element or a second electromagnetic transformer, the first switching means, and the second inductance element or And a fourth switching means inserted in series between the primary winding of the second electromagnetic transformer and a driving circuit of the piezoelectric transformer.
And switching the fourth switching means between the third switching means and the fourth switching means.
The predetermined frequency or the third frequency
Sixth control means for switching at a frequency of the second frequency, wherein the second or third control means sets the first switching means at a frequency which is an integer multiple of two or more of the predetermined frequency or the third frequency. The driving circuit for a piezoelectric transformer according to any one of claims 6 to 8, wherein the driving means is a control means for switching at the fourth frequency.

In this case, preferably, the fourth frequency is the predetermined frequency or twice the third frequency.

According to a twenty-first aspect, a difference is provided between a switching phase of the first switching means and a switching phase of the third and fourth switching means. Claim 19 or 20
A drive for the described piezoelectric transformer is provided.

According to Claim 22, the first and second electromagnetic transformers have a core, and the driving circuit of the piezoelectric transformer according to any one of Claims 19 to 21 is provided. Provided.

According to a twenty-third aspect of the present invention, there is provided the driving circuit for a piezoelectric transformer according to any one of the first to twenty-second aspects, wherein the power supply is a DC power supply.

According to a twenty-fourth aspect of the present invention, the first switching means operates in synchronization with an alternating current applied to the piezoelectric transformer. A transformer driving circuit is provided.

The on-duty ratio of the voltage applied to the driving means can be controlled between the input terminal connected to the power supply and the driving means capable of applying an alternating current to the piezoelectric transformer in accordance with the voltage from the power supply. By providing control means and switching means capable of controlling the power applied to the piezoelectric transformer, fluctuations in the power applied to the primary side of the piezoelectric transformer can be reduced or eliminated even when the power supply voltage fluctuates. Even if the voltage fluctuates, the load can be driven with constant power.

Further, even if the power supply voltage has various different values, the voltage-time product and the electric power applied to the driving means can be kept constant or equal to or less than a constant value. Since it is possible to use an element to be used whose power is equal to or less than a predetermined power allowance, the driving means can be made inexpensive and small accordingly. For example, when an inductance element, an electromagnetic transformer, or the like is used in the driving means, the inductance can be reduced, so that the element can be downsized. Furthermore, in the case where an electromagnetic transformer having a core is used, even if a core having a small size, for example, a core corresponding to the output voltage of the driving circuit of the piezoelectric transformer is used, it is possible to prevent the occurrence of magnetic saturation. Become like As a result, the size of the electromagnetic transformer can be reduced, and the driving circuit for the piezoelectric transformer can be made small and inexpensive.

Further, by providing a difference between the phase of the second switching means in the driving means and the phase of the first switching means inserted between the input terminal and the driving means, the first and the second switching means are provided. The noise voltage generated in the second switching means is dispersed. As a result, elements having a low withstand voltage can be used for the elements used for the first and second switching means, and the driving circuit for the piezoelectric transformer is small and inexpensive. It can be.

Also, according to the present invention, the input terminal to which the power supply is connected, and the voltage from the power supply which is inserted in series between the input terminal and the primary side of the piezoelectric transformer and is input to the input terminal The product of the AC voltage and time applied to the piezoelectric transformer according to the ratio of the time when the voltage is zero and the time when the voltage is positive or negative, the time integration of the voltage, the ratio of the ON time and the OFF time of the voltage or And a seventh control unit capable of controlling the on-duty ratio of the voltage.

Preferably, as the voltage from the power supply input to the input terminal increases, the seventh control means increases a product of an AC voltage and time applied to the piezoelectric transformer, a time integration of the voltage, The ratio of the time when the voltage is zero to the time when the voltage is positive or negative, the ratio of the on-time to the off-time of the voltage or the on-duty ratio of the voltage is reduced, and the voltage from the power supply input to the input terminal is reduced. The control means can be controlled to increase the product of the AC voltage and time applied to the piezoelectric transformer, the time integration of the voltage, the ratio of the ON time to the OFF time of the voltage, or the ON duty ratio of the voltage as the voltage becomes lower. .

According to the present invention, an input terminal to which a power supply is connected, and a voltage from the power supply which is inserted in series between the input terminal and the primary side of the piezoelectric transformer and is input to the input terminal And a control circuit for controlling the AC power applied to the piezoelectric transformer in accordance with the control circuit.

Preferably, the AC power applied to the piezoelectric transformer is equal to or less than a predetermined power or a constant power regardless of a voltage from the power supply input to the input terminal. Control means that can be controlled as described above.

Between the input terminal to which the power supply is connected and the primary side of the piezoelectric transformer, the product of the AC voltage and time applied to the piezoelectric transformer according to the voltage from the power supply, and the time and voltage when the voltage is zero A control means capable of controlling the ratio of the time during which the voltage is positive or negative, the time integration of the voltage, the ratio of the on-time to the off-time of the voltage or the on-duty ratio of the voltage, or the power of the AC applied to the piezoelectric transformer. Thereby, even if the power supply voltage fluctuates, the fluctuation of the power applied to the primary side of the piezoelectric transformer can be reduced or eliminated,
As a result, the load can be driven with constant power even when the power supply voltage fluctuates.

[0050]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram for explaining a driving circuit of a piezoelectric transformer according to the first and second embodiments of the present invention. FIG. 2 is a circuit diagram showing the first and second embodiments of the present invention. FIG. 6 is a waveform diagram for explaining a driving circuit of the piezoelectric transformer according to the embodiment.

As shown in FIG. 1, in this piezoelectric transformer driving circuit, a piezoelectric transformer driving circuit 70 for driving the piezoelectric transformer 80 is inserted in series between the input terminal 12 and the piezoelectric transformer 80, and further, the input terminal A switch Q3 is inserted in series between the driving circuit 12 and the piezoelectric transformer driving circuit 70. The switch Q3 and the piezoelectric transformer drive circuit 7
The diode D is connected between the connection point 0 and the ground. A load 90 is connected between the secondary electrode 83 of the piezoelectric transformer 80 and the ground.

The piezoelectric transformer drive circuit 70 includes two auto transformers 71 and 75, and the primary terminal of the auto transformer 71 and the primary terminal of the auto transformer 75 are both connected to the switch Q3, and the intermediate terminal of the auto transformer 71 and the ground. , A switch Q2 is connected between the intermediate terminal of the auto transformer 75 and the ground, and a secondary terminal of the auto transformer 71 is connected to the primary electrode 81 of the piezoelectric transformer 80. , Auto transformer 7
The secondary terminal 5 is connected to the primary electrode 82 of the piezoelectric transformer 80.

As shown in FIG. 2, the drive waveform φ1 of the switch Q1 and the drive waveform φ2 of the switch Q2 have the same frequency and a phase difference of 180 degrees. As a result, the auto transformer 7
1, 75, primary electrodes 81, 8 of the piezoelectric transformer 80.
2, voltages having opposite polarities are respectively applied.

The driving waveform φ3 of the switch Q3 is
1 and the drive waveform φ2 of the switch Q2. The frequency of the driving waveform φ3 is twice the frequency of the driving waveform φ1 or the driving waveform φ2. And the drive waveform φ
The on-duty ratio of 3 is determined according to the value of the input voltage Vin from the input power supply 10 applied to the input terminal 12.
That is, when the input voltage Vin is high, the on-duty ratio is small, and when the input voltage Vin is low, the on-duty ratio is controlled to be large.
The switching timing of the switch Q3 is controlled so that the power applied to the auto transformers 71 and 75 is equal to or less than a predetermined power or a predetermined power.

In this manner, the AC voltage VPT is applied between the primary electrodes 81 and 82 of the piezoelectric transformer 80 to drive the piezoelectric transformer 80. Based on the AC voltage VPT, the secondary voltage from the secondary electrode 83 is the same as the AC voltage VPT. The load 90 is driven by applying the frequency-boosted AC voltage to the load 90.

As described above, by controlling the switching timing of the switch Q3, the input voltage Vin is controlled.
Is high, the on-duty ratio is small, and if the input voltage Vin is low, the on-duty ratio is controlled to be large. Therefore, regardless of the value of the input voltage Vin, the power applied to the autotransformers 71 and 75 is constant. Or a predetermined power or less, so that the piezoelectric transformer 8
The power applied to the primary side of 0 may be a fixed power or a predetermined power or less. Therefore, the input voltage Vin
, The load 90 can be driven with a constant power or a predetermined power or less.

AC voltage V applied to piezoelectric transformer 80
PT is a value obtained by transforming the difference between the voltages applied to the switches Q1 and Q2 by the winding ratio of the auto transformer. Switch Q
1. To reduce the switching loss of Q2, VPT =
The inductance of the auto-transformer is designed so that a period of zero occurs. Since the voltage V1 of the switch Q1 is obtained by discharging the power stored in the primary side of the auto transformer while the switch Q1 is on when the switch Q1 is off, the voltage V1 has a half-sine waveform of a sine wave. .
This voltage has a value proportional to the power stored in the primary side of the auto-transformer 71 while Q1 is on. The power stored on the primary side of the auto transformer 71 can be controlled by controlling the on-duty ratio of the drive waveform φ3 of the switch Q3. That is, the voltage applied to the piezoelectric transformer 80 can be controlled by controlling the on-duty ratio of the drive waveform φ3 of the switch Q3.

Further, regardless of the value of the input voltage Vin, the power applied to the autotransformers 71 and 75 can be kept at a constant level or a predetermined level or less, so that the inductance of the autotransformers 71 and 75 can be reduced. As a result, the size of the autotransformers 71 and 75 can be reduced. Further, when using those having a core as the autotransformers 71 and 75, a core having a small size, for example,
Even if a core having a size corresponding to the output voltage of the piezoelectric transformer 80 is used, magnetic saturation can be prevented, and as a result, the size of the auto transformers 71 and 75 can be reduced. In this way, the autotransformers 71, 7
Since the size of the piezoelectric transformer can be reduced, the driving circuit of the piezoelectric transformer can be made small and inexpensive.

For example, when a lithium ion rechargeable battery is used as the input power source 10, there is a difference of about twice between the maximum value and the minimum value of the output voltage Vin. When an AC adapter is connected, the voltage is higher than the maximum value. Even in such a case, by controlling the on-duty ratio of the switch Q3, the power applied to the auto-transformers 71 and 75 is reduced to a predetermined power or less, or a fixed power, for example, a minimum output voltage of the lithium ion battery. The value can be used to design a power or lower.

Note that the switch Q
When 3 is off, the input voltage of the drive circuit 70 of the piezoelectric transformer can be reliably reduced to zero. Without the diode D, an excessive voltage may be applied to the switch Q3.

Also, as described above, the switches Q1, Q2,
When the switching operation of Q3 is performed simultaneously, as shown in FIG. 2 (see the waveform diagram of the voltage V1), the switches Q1, Q2,
Noise generated in Q3 may overlap, resulting in excessive noise.

Therefore, the drive waveform of the switch Q3 is changed to φ3 'in FIG. 2 so that the phase of the drive waveform φ3' of the switch Q3 and the phase of the drive waveform φ1 of the switch Q1 and the phase of the drive waveform φ2 of the switch Q2 are changed. By providing the difference, the switches Q1 and Q2 and Q3 are not switched at the same time, and the noise generated in the switches Q1, Q2 and Q3 is dispersed (see the waveform diagram of the voltage V1 'in FIG. 2). . As a result, switches having a low withstand voltage can be used for the switches Q1, Q2, and Q3, and the drive circuit of the piezoelectric transformer can be made small and inexpensive.

FIG. 3 is a block diagram for explaining a driving circuit of the piezoelectric transformer according to the first embodiment of the present invention, and FIG. 4 is a diagram illustrating a driving circuit of the piezoelectric transformer according to the first embodiment of the present invention. FIG. 3 is a waveform diagram for explaining a circuit.

The drive circuit 100 for the piezoelectric transformer is connected to an input power supply 10 and receives an input voltage Vin from the input power supply 10.
, A current-voltage conversion circuit 20 for converting a load current flowing through a load 90 connected to the piezoelectric transformer 80 into a DC voltage, a reference voltage generation circuit 62 for generating a reference voltage Vref, The error amplifier 32 compares the reference voltage Vref from the voltage generation circuit 62 with the output voltage from the current-to-voltage conversion circuit 20 and amplifies and outputs an error between the reference voltage Vref and the output voltage from the error amplifier 32. A voltage signal Vf of a triangular wave, which outputs a higher frequency voltage signal Vf when the output voltage from the error amplifier 32 increases, and outputs a lower frequency signal when the output voltage from the error amplifier 32 decreases. The voltage-frequency conversion circuit 36 that outputs the voltage signal Vf, and the input voltage Vin are compared with the reference voltage Vref by the reference voltage generation circuit 62 to amplify an error therebetween. An error amplifier 34 which outputs a DC voltage Ve, and the voltage signal Vf of the triangular wave, the comparator 42 for comparing the DC voltage Ve across it, and outputs a rectangular wave φ3
And a divide-by-two circuit 44 that divides the rectangular wave φ3 by 2 to output a rectangular wave φ1, and an inverter (inverted logic circuit) 52 that outputs a rectangular wave φ2 180 ° out of phase with the rectangular wave φ1.
, A piezoelectric transformer driving circuit 70 for driving the piezoelectric transformer 80, and a switch Q3 inserted in series between the piezoelectric transformer driving circuit 70 and the input terminal 12. As shown in FIG. 1, the piezoelectric transformer drive circuit 70 includes auto transformers 71 and 75 and switches Q1 and Q2. The above is the case where the reference voltage is input to the negative input of the error amplifier, but when the polarity of the error amplifier input is reversed,
The change in frequency is reversed.

The piezoelectric transformer driving circuit 70 drives the piezoelectric transformer 80 to supply power to the load (CCFL) 90. The load current is converted into a voltage by the current-voltage conversion circuit 20 and compared with the reference voltage Vref.
2 is obtained. The voltage-frequency conversion circuit 36 generates a triangular wave signal Vf having a frequency corresponding to the output voltage, and based on the generated signal, adjusts the driving frequency of the piezoelectric transformer 80 and controls the load current to be constant.

On the other hand, the voltage-time product or power supplied to the piezoelectric transformer drive circuit 70 is controlled by the switch Q3, and the elements of the piezoelectric transformer drive circuit 70 (electromagnetic autotransformers 71 and 75) are prevented from being saturated.

That is, the error amplifier 34 outputs the input voltage V
In is compared with the reference voltage Vref to generate a DC voltage Ve. The comparator 42 compares the triangular wave signal Vf with the DC voltage Ve crossing the triangular wave signal Vf to obtain a rectangular wave φ3. This rectangular wave φ3 is turned off when the DC voltage is larger than the triangular wave signal Vf, and is turned off when the DC voltage is small.
It becomes N. This rectangular wave φ3 becomes the drive waveform of the switch Q3. Thus, the frequency of the rectangular wave φ3 is determined by the load current and the reference voltage Vref, and the on-duty ratio is determined based on the input voltage Vin. When the input voltage Vin is high, the on-duty ratio decreases, and when the input voltage Vin is low, the on-duty ratio increases. In this way, by controlling the switching timing of the switch Q3, the voltage-time product or power supplied to the piezoelectric transformer drive circuit 70 is controlled by the switch Q3.

By dividing the driving waveform φ3 of the switch Q3 by 2 by the divide-by-2 circuit 44, the switch Q1
Is obtained, and the inverter 52 inverts the logic of the rectangular wave φ1 to obtain a rectangular wave φ2 180 ° out of phase with the rectangular wave φ1 to obtain a drive waveform for the switch Q2. The frequency of rectangular wave φ3 is rectangular wave φ
1, which is twice the frequency of φ2, and the phase of the rectangular wave φ3 coincides with the phase of the rectangular waves φ1 and φ2.

FIG. 5 is a block diagram for explaining a driving circuit of a piezoelectric transformer according to a second embodiment of the present invention. FIG. 6 is a block diagram showing a driving circuit of the piezoelectric transformer according to the second embodiment of the present invention. FIG. 3 is a waveform diagram for explaining a circuit.

In the first embodiment, the rectangular wave φ3 is frequency-divided by 2 by the divide-by-2 circuit 44 to obtain the rectangular wave φ1, but in the present embodiment, the output voltage Ve of the error amplifier 34 and the voltage A reference voltage generation circuit 64 for generating a reference voltage Ve ′ having a different value is provided. The comparator 46 compares the reference voltage Ve ′ with the triangular wave signal Vf from the voltage-frequency conversion circuit 36 to obtain a rectangular wave φ4. This rectangular wave φ4 is divided by 2
4 to obtain a rectangular wave φ1 which is the drive waveform of the switch Q1, and the inverter 52 inverts the logic of the rectangular wave φ1 so that the rectangular waves φ1 and 1
A rectangular wave φ2 having a phase difference of 80 degrees is obtained and used as a drive waveform of the switch Q2. The frequency of the rectangular wave φ3 is rectangular wave φ1, φ2
Of the square wave φ3 and the phase of the square wave φ
1, the phases of φ2 are different. The other points are the same as the first embodiment.

Although the automatic transformers 71 and 75 are used in the first and second embodiments, other electromagnetic transformers whose primary and secondary sides are insulated may be used instead. It is possible to use an inductance element instead of an electromagnetic transformer.

[0073]

EXAMPLES Table 1 shows Examples 1 and 2 of the present invention and Comparative Examples. Example 1 uses the drive circuit of the first embodiment, Example 2 uses the drive circuit of the second embodiment, and the comparative example excludes the switch Q3 from the circuit of the example. One used.

[0074]

[Table 1]

As described above, in the first and second embodiments of the present invention using the switch Q3, a large maximum input voltage was obtained with a small core size. On the other hand, in Comparative Example 1 in which the switch Q3 is not used, the maximum input voltage is small.
It was necessary to increase the core size.

Further, as in the first embodiment. By providing a phase difference, noise could be reduced.

[0077]

The power applied to the primary side of the piezoelectric transformer can be reduced or eliminated even if the power supply voltage fluctuates. As a result, even if the power supply voltage fluctuates, the load can be driven with constant power. can do.

Further, even if the power supply voltage has various different values, the voltage-time product and the power applied to the driving means for driving the piezoelectric transformer can be kept constant or equal to or less than the fixed value. As a result, it is possible to use an element used for the drive unit that has a power allowance value equal to or less than a predetermined value, and the drive circuit for the piezoelectric transformer can be made inexpensive and small accordingly.

When an inductance element, an electromagnetic transformer, or the like is used in the driving means, the inductance can be reduced, so that the element can be downsized.

Further, in the case where an electromagnetic transformer having a core is used, saturation of the core can be prevented even if a core having a small size is used. As a result, the size of the electromagnetic transformer can be reduced, and the driving circuit for the piezoelectric transformer can be made small and inexpensive.

Also, by providing a difference between the phase of the second switching means in the driving means and the phase of the first switching means inserted between the input terminal and the driving means, the first and the second switching means are provided. The noise voltage generated in the second switching means is dispersed. As a result, elements having a low withstand voltage can be used for the elements used for the first and second switching means, and the driving circuit for the piezoelectric transformer is small and inexpensive. It can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram for explaining a driving circuit of a piezoelectric transformer according to first and second embodiments of the present invention.

FIG. 2 is a waveform diagram for explaining a driving circuit of the piezoelectric transformer according to the first and second embodiments of the present invention.

FIG. 3 is a block diagram for explaining a driving circuit of the piezoelectric transformer according to the first embodiment of the present invention.

FIG. 4 is a waveform diagram for explaining a driving circuit of the piezoelectric transformer according to the first embodiment of the present invention.

FIG. 5 is a block diagram for explaining a driving circuit of a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 6 is a waveform diagram for explaining a driving circuit of a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 7 is a circuit diagram for explaining a conventional piezoelectric transformer drive circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Input power supply 12 ... Input terminal 20 ... Current-voltage conversion circuit 32, 34 ... Error amplifier 36 ... Voltage-frequency conversion circuit 42, 46 ... Comparator 44 ... Divide-by-two circuit 52 ... Inverter (inverting logic circuit) 62 Reference numeral 64: Reference voltage generating circuit 70: Piezoelectric transformer driving circuit 71, 75 ... Auto transformer 80: Piezoelectric transformer 81, 82 ... Primary electrode 83 ... Secondary electrode 90: Load 100, 200, 300 ... Piezoelectric transformer driving circuit D ... diodes Q1, Q2, Q3 ... switches

Claims (24)

[Claims] An input terminal connected to a power supply; a driving unit capable of applying an alternating current of a predetermined frequency to a primary side of a piezoelectric transformer; and an input terminal inserted between the input terminal and the driving unit. A driving unit for controlling an on-duty ratio of a voltage applied to the driving unit in accordance with a voltage from the power source input to the driving unit. 2. The control means decreases the on-duty ratio of a voltage applied to the driving means as the voltage from the power supply input to the input terminal increases, and 2. The piezoelectric transformer drive circuit according to claim 1, wherein the control means is a control means which can control the on-duty ratio of the voltage applied to the drive means to increase as the voltage from the power supply decreases. 3. An input terminal to which a power supply is connected; driving means capable of applying an alternating current of a predetermined frequency to a primary side of a piezoelectric transformer; and said input terminal inserted between said input terminal and said driving means. And a control means for controlling power applied to the drive means in accordance with a voltage from the power supply input to the drive circuit. 4. A control capable of controlling the electric power applied to the driving means to be equal to or less than a predetermined electric power or a constant electric power irrespective of a voltage from the power supply inputted to the input terminal. 4. The driving circuit for a piezoelectric transformer according to claim 3, wherein said driving circuit is a means. 5. An input terminal to which a power supply is connected, driving means capable of applying an alternating current of a predetermined frequency to a primary side of a piezoelectric transformer, and a driving means inserted in series between the input terminal and the driving means. A driving circuit for a piezoelectric transformer, comprising: 6. The apparatus according to claim 5, further comprising a second control unit capable of controlling an on-duty ratio of said first switching unit in accordance with a voltage from said power supply input to said input terminal. A driving circuit for the piezoelectric transformer described in the above. 7. The second control means decreases the on-duty ratio of the first switching means as the voltage from the power supply input to the input terminal increases, and the second control means 7. The driving circuit for a piezoelectric transformer according to claim 6, wherein the control means is a control means capable of controlling the on-duty ratio of the first switching means to increase as the voltage from the power supply decreases. 8. The switching of the first switching means so that the power applied to the driving means is equal to or less than a predetermined power or a constant power irrespective of a voltage from the power supply inputted to the input terminal. 6. The piezoelectric transformer drive circuit according to claim 5, further comprising third control means capable of controlling timing. 9. A first control signal having a first frequency is generated based on a signal from an input terminal to which a power supply is connected and a load driven by a piezoelectric transformer. And a second control signal having a second frequency of a frequency that is an integer multiple of 2 or more of the first frequency based on the signal from the power supply input to the input terminal. Fourth control means for generating the second control signal having a duty; and n times or 1 / n times (n) times the first frequency on the primary side of the piezoelectric transformer based on the first control signal. Is an integer of 1 or more.) A driving means capable of applying an AC having a third frequency of a frequency of: and a first switching means inserted in series between the input terminal and the driving means. , By the second control signal The second a frequency, said third piezoelectric transformer drive circuit, characterized in that it comprises, a first switching means which is switched in two or more integral multiple of the frequency of the frequency. 10. The fourth control means decreases the on-duty ratio as the voltage from the power supply input to the input terminal increases, and the voltage from the power supply input to the input terminal decreases. 10. The driving circuit for a piezoelectric transformer according to claim 9, wherein the control unit increases the on-duty ratio as the value decreases. 11. An input terminal to which a power supply is connected, a first circuit for generating a first signal of a first frequency based on a signal from a load driven by a piezoelectric transformer, and the first signal N or 1 / n times the first frequency (where n is 1) based on and the voltage input to the input terminal.
Is an integer greater than or equal to. ), A second signal having a second frequency having a predetermined on-duty ratio.
A second circuit for generating a signal of the third frequency; and a third circuit of a third frequency of a frequency that is an integral multiple of 2 or more of the second frequency based on the first or second signal.
A driving circuit capable of applying an alternating current of the third frequency to the primary side of the piezoelectric transformer based on the third signal; A first switching means inserted in series between the first and second switching means, wherein the first switching means is switched at the second frequency by the second signal. Drive circuit. 12. The second circuit, as the voltage from the power supply input to the input terminal increases, the on-duty ratio decreases, and the voltage from the power supply input to the input terminal decreases. 12. The piezoelectric transformer drive circuit according to claim 11, wherein the circuit is configured to increase the on-duty ratio as the value decreases. 13. The apparatus according to claim 1, wherein said driving means includes an inductance element.
3. The driving circuit for a piezoelectric transformer according to any one of 2. 14. The driving circuit for a piezoelectric transformer according to claim 1, wherein said driving means includes an electromagnetic transformer. 15. The driving circuit according to claim 14, wherein said electromagnetic transformer has a core. 16. The switching means inserted in series between the control means or the first switching means, and the inductance element or the primary winding of the electromagnetic transformer, the driving means comprising: The piezoelectric transformer according to any one of claims 13 to 15, further comprising: a fifth control unit that switches the second switching unit at the predetermined frequency or the third frequency. circuit. 17. A second switching device, wherein said drive means is inserted in series between an inductance element or an electromagnetic transformer, said first switching means, and a primary winding of said inductance element or said electromagnetic transformer. Means, and fifth control means for switching the second switching means at the predetermined frequency or the third frequency, wherein the second or third control means performs the first switching. 9. The piezoelectric transformer according to claim 6, wherein the switching means is switching means for switching at a predetermined frequency or a fourth frequency which is an integer multiple of two or more of the third frequency. Drive circuit. 18. The apparatus according to claim 1, wherein a difference is provided between a switching phase of said first switching means and a switching phase of said second switching means.
18. The driving device for a piezoelectric transformer according to 6 or 17. 19. The driving means, comprising: a first inductance element or a first electromagnetic transformer; the control means or the first switching means; and a primary of the first inductance element or the first electromagnetic transformer. A third switching means inserted in series between the side windings, a second inductance element or a second electromagnetic transformer, the control means or the first switching means, and the second inductance element Or a fourth switching means inserted in series between the primary winding of the second electromagnetic transformer and a driving circuit of the piezoelectric transformer, wherein the third and fourth switching means include: The third switching means and the fourth switching means are 180 degrees out of phase with each other so that the predetermined frequency or the third Piezoelectric transformer drive circuit according to any one of claims 1 to 12, further comprising a sixth control means for switching the frequency. 20. The driving device, comprising: a first inductance element or a first electromagnetic transformer; the first switching means; and a primary winding of the first inductance element or the first electromagnetic transformer. A third switching means inserted in series between the second switching element, a second inductance element or a second electromagnetic transformer, the first switching means, and the second inductance element or the second electromagnetic transformer. And a fourth switching means inserted in series between the primary winding and the primary winding. The driving circuit for the piezoelectric transformer includes the third and fourth switching means, the third switching means and the third switching means. A sixth control in which the phase is made different by 180 degrees from the fourth switching means to switch at the predetermined frequency or the third frequency. Means for controlling the second or third control means to switch the first switching means at a fourth frequency of the predetermined frequency or an integer multiple of two or more of the third frequency. 9. The driving circuit for a piezoelectric transformer according to claim 6, wherein the driving circuit is a means. 21. The apparatus according to claim 19, wherein a difference is provided between a switching phase of said first switching means and a switching phase of said third and fourth switching means. Drive device for piezoelectric transformer. 22. The first and second electromagnetic transformers include:
22. The device according to claim 19, further comprising a core.
The driving circuit for a piezoelectric transformer according to any one of the above. 23. The driving circuit for a piezoelectric transformer according to claim 1, wherein said power supply is a DC power supply. 24. The piezoelectric transformer driving circuit according to claim 1, wherein said first switching means operates in synchronization with an alternating current applied to said piezoelectric transformer.