JPH0739146A - Piezoelectric transformer - Google Patents

Abstract

PURPOSE:To eliminate the occurrence of a spurious modulation and to stabilize an output voltage by a method wherein the number of electrode pairs of input electrodes is made identical to the number of electrode pairs of output electrodes and the opposite length of the electrode pairs of the input electrodes is made longer than the opposite length of the electrode pairs of the output electrodes. CONSTITUTION:An input electrode 42 and an output electrode 43 are arranged in the direction in a length L of a piezoelectric-substance substrate 41. The input electrode 42 is provided with a plurality of electrode pairs 48 which are constituted of a finger electrode 44 and a comb tooth-shaped electrode 45 as well as of a finger electrode 46 and a comb tooth-shaped electrode 47, and the output electrode 43 is provided with a plurality of electrode pairs 54 which are constituted of a finger electrode 50 and a comb tooth-shaped electrode 51 as well as of a finger electrode 52 and a comb tooth-shaped electrode 53. Then, the electrode pairs 48 and the electrode pairs 54 are arranged synchronously at the same pitch, and the number of the electrode pairs 48 is made identical to the number of the electrode pairs 54. In addition, the opposite length L1 of the finger electrodes 44, 46 constituting the electrode pairs 48 is made longer than the opposite length L2 of the finger electrodes 50, 52 constituting the electrode pairs 54.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer, and more particularly to a piezoelectric transformer utilizing the width-sliding vibration of a piezoelectric substrate.

Along with the miniaturization of electronic devices, the transformers incorporated therein have also been required to be compact and lightweight.

Therefore, at present, attention is focused on a piezoelectric transformer which can be made much smaller and lighter than the conventional electromagnetic transformer.

The piezoelectric transformer is required to have stable characteristics and have no problem in supporting it on the circuit board.

[0005]

2. Description of the Related Art Conventional piezoelectric transformers generally utilize the lateral effect vibration of a piezoelectric substrate.

In this piezoelectric transformer, since the piezoelectric substrate vibrates in the thickness direction, when the piezoelectric transformer is supported on the circuit substrate, stress concentrates on the supported portion and the piezoelectric substrate is broken. Was happening.

To solve this problem, the applicant of the present invention has further proposed a piezoelectric transformer using the width-sliding vibration of the piezoelectric substrate.

FIG. 9 shows the piezoelectric transformer 10.

The piezoelectric transformer 10 is made of Li having a length L and a width W.
An input electrode 12 is provided over the entire width of the upper surface 11a of the NbO ₃ piezoelectric substrate 11 and at both ends in the width direction of the lower surface 11b. This is the configuration provided.

The input electrode 12 and the output electrode 13 have electrode pairs 14 and 15 arranged periodically.

The number N ₂ of electrode pairs 15 of the output electrode 13 is smaller than the number N ₁ of electrode pairs 14 of the input electrode 12. As a result, the output electrode 13 has a higher impedance than the input electrode 12, and the boost ratio exceeds "1".

When a voltage having a predetermined frequency is applied to the input electrode 12, the piezoelectric substrate 11 is distorted as shown by an arrow 16 in FIG. 10 to cause width-sliding vibration in the direction of the length L, and the piezoelectric substrate 11, a standing wave 15 stands in the width W direction,
An alternating voltage is generated in the polarization direction. The output electrode 13 detects this AC voltage.

As shown in FIG. 11, the piezoelectric transformer 10 is supported on the circuit board 19 by soldering the portions on both ends in the length L direction of the piezoelectric substrate 11 with solder 18. .

Since the direction of vibration of the piezoelectric substrate 11 is the direction of the length L, stress concentration does not occur in the soldered portion, and the piezoelectric transformer 10 is supported without any trouble.

[0015]

However, since the piezoelectric transformer 10 described above has N ₂ ≠ N ₁ , the piezoelectric transformer 1
The admittance-frequency characteristic of 0 is as shown by the line I in FIG. 12, and as shown by the reference numeral 20, spurious in the higher mode is generated.

When this high-order mode spurious 20 occurs, the step-up ratio fluctuates due to this, and there is a problem that the piezoelectric transformer 10 cannot stably output a predetermined output voltage.

Here, the reason why spurious occurs will be briefly described.

When N ₂ = N ₁ , the transfer characteristic (frequency response characteristic) of the output electrode is as shown by the line II in FIG. 13 and the width generated on the piezoelectric substrate by the input electrode. The frequency f _{n of the} sliding vibration and the frequencies f _{n + 1} , f _{n + 2} ..., F _n-1 , f _{n-2 of} the harmonics thereof are the same as those in FIG.
It becomes as shown in.

As can be seen from FIG. 13, except for the frequency f _n , the pole of the transfer characteristic of the output electrode is the high frequency f
_{n + 1} , f _{n + 2} ..., F _n-1 , f _n-2 ...

Therefore, the output electrode can extract only the frequency f _n .

Like the piezoelectric transformer 10 described above, N ₂ ≠
In the case of N ₁ , the transfer characteristic of the output electrode is shown by the line in FIG.
As shown in III, the poles of the transfer characteristic are frequencies f _{n + 1} and f
_{n + 2} ..., fn _-1 , fn _-2 ... Do not match.

Therefore, the frequency f_{n + 1}, F_{n + 2}…, F
_n-1, F_n-2, F_n-4Also at point P ₁~ P_FiveCorresponds to
Gain, which causes the above spurious emission.
I will live.

The present invention eliminates the generation of spurious,
An object of the present invention is to provide a piezoelectric transformer that realizes stabilization of output voltage.

[0024]

According to the present invention, an input electrode and an output electrode are provided on a piezoelectric substrate, and the input electrode and the output electrode are composed of a pair of electrodes arranged periodically, and the input electrode is the piezoelectric body. A piezoelectric transformer in which a substrate is subjected to width-slip vibration and the output voltage outputs a voltage, wherein the input electrode (42) and the output electrode (43) are substantially equal in number (N ₁₀ =
N ₁₁ ) electrode pairs (48, 57) and the opposing length (L ₁ ) of the output electrode electrode pair (54) to the input electrode electrode pair (48) opposing length (L ₁ ). ₂ ) to ratio (L
₁ / L ₂ ) is configured to have a value exceeding 1.

[0025]

The structure in which the number of the electrode pairs of the input electrodes and the number of the electrode pairs of the output electrodes are the same serves to prevent spurious emission from occurring.

The configuration in which the ratio of the facing length of the electrode pair of the input electrode to the facing length of the electrode pair of the output electrode is set to a value exceeding 1 works so that the step-up ratio is set to a value exceeding 1.

[0027]

[First Embodiment] FIG. 1 shows a piezoelectric transformer 40 according to a first embodiment of the present invention. The piezoelectric transformer 40 includes a piezoelectric substrate 41 of LiNbO ₃ having a length L and a width W, and an input electrode 42 and an output electrode 43 on an upper surface 41 a of the piezoelectric substrate 41.

The input electrode 42 and the output electrode 43 extend over the entire width W of the piezoelectric substrate 41.

The input electrode 42 and the output electrode 43 are arranged side by side in the direction of the length L of the piezoelectric substrate 41.

The input electrode 42 has a structure in which a comb-shaped electrode 45 having a plurality of finger electrodes 44 and a comb-shaped electrode 47 having a plurality of finger electrodes 46 are arranged in a meshed state, and are arranged periodically. It has N ₁₀ electrode pairs 48.

In each electrode pair 48, the finger electrode 44
The length (hereinafter, referred to as a facing length) of the portion where and 46 are facing each other is L ₁ .

The output electrode 43 has a structure in which a comb tooth-shaped electrode 51 having a plurality of finger electrodes 50 and a comb tooth-shaped electrode 52 having a plurality of finger electrodes 52 are arranged in a meshed state.

The output electrode 43 has a plurality of electrode pairs 54. The electrode pairs 54 are periodically arranged at the same pitch as the electrode pairs 48 of the input electrode 42.

The number N ₁₁ of electrode pairs 54 is the same as the number of electrode pairs 48 of the input electrode 42. N ₁₁ = N ₁₀ .

The finger electrodes 50 forming the electrode pair 54,
The facing length of 52 is L ₂ . L ₂ is shorter than L ₁ and L ₂ <L ₁ .

Between the input electrode 42 and the output electrode 43,
The electrodeless strip 55 is present, and the electrodes 42 and 43 are separated from each other by the dimension A.

Reference numeral 56 is an input terminal, and 57 is an output terminal.

An equivalent circuit of the piezoelectric transformer 40 having the above structure is as shown in FIG.

Reference numeral 60 is an equivalent circuit of the input electrode 42, 6
Reference numeral 1 is an equivalent circuit of the output electrode 43. Input electrode 4
2 and the dimensions of each part of the output electrode 43 are appropriately determined, and the resonance frequencies fr of the respective equivalent circuits are equal to each other.

Ck is a coupling capacitor, and has a capacitance corresponding to the electrodeless strip 55.

As in the case of FIG. 11, the piezoelectric transformer 40 is supported on the circuit board 59 by soldering both ends in the length L direction of the piezoelectric substrate 41 with the solder 58.

Next, the operation of the piezoelectric transformer 40 will be described.

The piezoelectric transformer 40 uses the results of the experiments by the inventors described below.

The present inventor manufactured a device in which the ratio of the facing length L ₁ of the input electrode to the facing length L ₂ of the output electrode was appropriately changed, and the voltage V _{1 of a} predetermined frequency was applied to the input electrode to actually perform the production. The piezoelectric transformer was driven, the output voltage V ₂ was measured, and the step-up ratio (V ₂ / V ₁ ) was determined.

As a result, the result shown by line IV in FIG. 3 was obtained.

That is, the facing length ratio (L₁/ L₂) Changes
And the step-up ratio (V₂/ V ₁) Change and face
Length ratio (L₁/ L₂) Is 1.0 or more, the step-up ratio (V
₂/ V₁) Was 1.0 or higher.

In the piezoelectric transformer 40 of the above embodiment,
When the input power V ₁ having the resonance frequency fr is applied to the input terminal 56, the piezoelectric substrate 41 causes width-sliding vibration as in the case shown in FIG.

Due to this vibration, energy having a distribution indicated by reference numeral 62 in FIG. 1 is generated.

The vibration energy is transmitted in the length L direction on the upper surface 41a of the piezoelectric substrate 41, exceeds the electrodeless band portion 55, and reaches the portion where the output electrode 43 is formed.

As a result, the output electrode 43 is connected to the input electrode 42 as shown by the arrow 63.

As a result, the output electrode 43 is connected to the piezoelectric substrate 4
The voltage generated by the polarization generated in the part where the output electrode 43 is formed is detected.

The output terminal 57 allows the frequency to be the resonance frequency.
f₁Has a frequency equal to ₂Is the input voltage V₁Yo
Higher voltage is taken out.

The number N ₁₁ of finger electrodes of the output electrode 43 is equal to the number N ₁₀ of finger electrodes of the input electrode 42.

Therefore, the admittance-frequency characteristic of the piezoelectric transformer 40 is as shown by the line V in FIG. 4, and spurious is not generated.

Therefore, the boosting ratio is stable and the stable output voltage V ₂ is taken out. [Modification of the First Embodiment] The piezoelectric transformer 40 shown in FIG.
The width A of the electrodeless strip portion 55 may be appropriately changed.

When the electrodeless portion 55 is wide, the output electrode 4
The degree of coupling of No. 3 to the input electrode 42 is small.

When the electrodeless portion 55 is narrow, the output electrode 4
The degree of coupling of No. 3 to the input electrode 42 is increased.

The piezoelectric transformer has characteristics corresponding to the degree of coupling. [Second Embodiment] FIGS. 5A and 5B show a piezoelectric transformer 70 according to a second embodiment of the present invention.

In the figure, the parts substantially corresponding to the constituent parts shown in FIG. 1 are designated by the same reference numerals with a suffix A.

In the piezoelectric transformer 70, the input electrode 42A is provided on the upper surface 41Aa of the piezoelectric substrate 41A, and the output electrode 43A is provided.
Of the lower surface 41Ab of the piezoelectric substrate 11A.
This is a configuration provided directly below 1A.

The output electrode 43A is in the direction shown by the arrow 71,
That is, in the direction of the thickness t of the piezoelectric substrate 41A, the input electrode 42
It is connected with A.

As viewed from the upper surface 41Aa side of the piezoelectric substrate 41A, the entire facing length L ₂ of the output electrode 43A is included within the range of the facing length L ₁ of the input electrode 42A.

The piezoelectric transformer 70 having the above-described structure has the characteristic that the step-up ratio is stable, like the piezoelectric transformer 40 of FIG.

In the piezoelectric transformer 70 described above,
By using piezoelectric substrates 41A having different thicknesses t, the degree of coupling of the output electrode 43A to the input electrode 42A can be appropriately changed. [First Modification of Second Embodiment] The piezoelectric transformer 70A shown in FIGS. 6A and 6B has an output electrode 43B on the lower surface 41Bb.
On the upper surface 41Ba in the direction of the length L of the piezoelectric substrate 41B.
The input electrode 42B is slightly displaced from the input electrode 42B.

Of the length L _{2 in} the direction of the electrode pair of the output electrode 43B, the length B is out of the range of the facing length L ₁ of the electrode pair of the input electrode 42B.

The degree of coupling of the output electrode 43B to the input electrode 42B is weaker than that of the piezoelectric transformer 70 of FIG. 5, and the piezoelectric transformer 70A has characteristics corresponding to the degree of coupling. [Second Modification of Second Embodiment] The piezoelectric transformer 70B shown in FIGS. 7A and 7B has an upper surface 41Ca of a piezoelectric substrate 41C.
Input electrode 42C and output electrode 43C on the lower surface 41Cb
In the direction of the length L of the piezoelectric substrate 41C, they are arranged so as to be displaced in mutually opposite directions.

A portion of the output electrode 43C having a facing length L ₂ of the electrode pair is offset from the portion of the input electrode 42C having a length L _{1 in} the direction of the electrode pair by a length C.

The degree of coupling of the output electrode 43C to the input electrode 42C is weaker than that of the piezoelectric transformer 70A shown in FIG. 6, and the piezoelectric transformer 70B has a characteristic corresponding to the degree of weak coupling. [Third Embodiment] FIGS. 8A and 8B show a piezoelectric transformer 80 according to a third embodiment of the present invention.

An input electrode 42D is provided on the upper surface 43Da of the piezoelectric substrate 43D, and two output electrodes 4 are provided on the lower surface 43Db.
3Da and 43Db are arranged side by side.

The output electrode can be selectively taken out in three modes.

First, the terminal 57 of the output electrode 43Da.
The first output voltage is taken out from a and 57b.

Second, the terminal 57 of the output electrode 43Db.
The second output voltage is taken out from c and 57d.

Thirdly, by electrically connecting a tap (not shown) connected to the terminal 57b and a tap (not shown) connected to the terminal 57c, output powers 43Da and 43Db are obtained. With the configuration in which and are electrically connected in series, the third output voltage is taken out from the terminals 57a and 57d.

In each of the piezoelectric transformers 70, 70A, 70B and 80 of the second embodiment, its modification and the third embodiment, the number of electrode pairs of output electrodes is set equal to the number of electrode pairs of input electrodes. is there. Therefore, the generation of spurious is suppressed, and each piezoelectric transformer 70, 70A, 70B, 80
Outputs a voltage with a stable voltage value.

[0075]

As described above, according to the piezoelectric transformer of the present invention, not only the mounting problem can be solved but also spurious can be effectively prevented.

Since the generation of spurious is suppressed, the boost ratio can be prevented from fluctuating, and the characteristics can be stabilized.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an equivalent circuit of the piezoelectric transformer of FIG.

FIG. 3 is a diagram showing a relationship between a directional length ratio and a step-up ratio obtained by an experiment by the present inventor.

FIG. 4 is a diagram showing admittance-frequency characteristics of the piezoelectric transformer of FIG.

FIG. 5 is a diagram showing a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a piezoelectric transformer according to a first modification of the second embodiment.

FIG. 7 is a diagram showing a piezoelectric transformer according to a second modification of the second embodiment.

FIG. 8 is a diagram showing a piezoelectric transformer according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a piezoelectric transformer previously proposed by the applicant.

10 is a diagram for explaining width-sliding vibration of the piezoelectric substrate in FIG.

FIG. 11 is a view showing a supporting state of the piezoelectric transformer of FIG.

12 is a diagram showing admittance-frequency characteristics of the piezoelectric transformer of FIG.

FIG. 13 is a diagram illustrating that the spurious of FIG. 12 occurs in the piezoelectric transformer of FIG.

[Explanation of symbols]

17 Standing waves of width sliding vibration 41, 41A, 41B, 41C, 41D Piezoelectric substrate 41a, 41Aa, 41Ba, 41Ca, 41Da Upper surface 41Ab, 41Bb, 41Cb, 41Db Lower surface 42, 42B, 42C, 42D Input electrode 43, 43B , 43C, 43Da, 43Db Output electrode 44, 46, 50, 52 Finger electrode 45, 47, 51, 53 Comb-shaped electrode 48, 54 Electrode pair 55 Electrode strip 56 Input terminal 57, 57A to 57D Output terminal 58 Solder 59 Circuit board 60 Equivalent circuit of input electrode portion 61 Equivalent circuit of output electrode portion 62 Vibration energy 63,71 generated by application of input electrode to input electrode 63, 71 Arrow indicating coupling

Claims (1)

[Claims] 1. A piezoelectric substrate is provided with an input electrode and an output electrode, and the input electrode and the output electrode are composed of electrode pairs arranged periodically, and the input electrode vibrates the piezoelectric substrate in a width-sliding vibration. A piezoelectric transformer that outputs an output voltage, wherein the input electrode (42) and the output electrode (43) have substantially the same number (N ₁₀ = N ₁₁ ) of electrode pairs (48, 57). and, opposing length of the electrode pairs of the input electrode (48) facing the length of (L ₁₎ electrode pair of the output electrodes (54) the ratio _{(L 2) (L 1 /} L 2) is 1 A piezoelectric transformer having a configuration having a value exceeding the above.