JPH10200174A - Tertiary rosen type piezo-electric transformer and its driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tertiary Rosen piezo-electric transformer and its driving circuit by which leak current can be reduced when loaded and a high-frequency voltage with stabilized high voltage be applied to load by insulating circuits on the primary and secondary sides of a piezo-electric transformer so as to reduce the floating capacitance to the most extent when loaded. SOLUTION: An a.c. voltage is applied to input electrodes 2a, 2b, 3a, and 3b of a tertiary Rosen type piezo-electric transformer 1 from an input source 7. A balanced voltage is applied to a load RL from output electrodes 5 and 6, and the load is floated from the earth. A current detection circuit 8 comprised of a resistor R2b, a capacitor C and a diode D is provided to the input electrode 2b to detect a load current io. Since the load current io is shouted to the input electrodes 3a and 2a and input electrodes 3b and 2b, it can be detected by using the voltage drop of the resistor R2b. As being different from the case where the circuit 8 is provided to the load RL side, no large floating capacitance is generated in the load RL and leak current can be reduced greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tertiary Rosen-type piezoelectric transformer used for a cold-cathode tube lighting inverter of a backlight of a liquid crystal display such as a personal computer and a word processor, and a driving circuit therefor.

[0002]

2. Description of the Related Art FIG. 4 is a perspective view of a piezoelectric transformer used in a conventional cold-cathode tube lighting inverter. In the figure, 10 is a secondary Rosen type piezoelectric transformer, 12
Reference numerals a and 12b denote input electrodes provided on one side, and reference numeral 15 denotes an output electrode provided on the side opposite to the input electrodes 12a and 12b. At the positions of the input electrodes 12a and 12b, polarization is performed in the thickness direction as indicated by arrows, and the other portions are polarized in the longitudinal direction as indicated by arrows.

A high-frequency voltage having a resonance frequency is applied to the input electrodes 12 a and 12 b of the secondary Rosen-type piezoelectric transformer 10 to resonate, and a high-frequency high voltage is obtained from the output electrode 15.

The secondary Rosen type piezoelectric transformer 10 has a unique vibration mode, and has two nodes (portions where vibration does not occur, which are called node points). Since the support at the vibrating part causes a reduction in efficiency due to the inhibition of the vibration, the supporting position is restricted. In addition, there is a drawback that the connection portions of the input / output lead wires to the input electrodes 12a, 12b and the output electrode 15 are vibrating portions and lead to disconnection of the lead wires.

FIG. 5 is a perspective view of a piezoelectric transformer used in another conventional cold-cathode tube lighting inverter.
In the figure, reference numeral 20 denotes a tertiary Rosen type piezoelectric transformer, 22
Reference numerals a, 22b, 23a, and 23b denote input electrodes provided on both sides, and reference numeral 25 denotes an output electrode provided in the center. Input electrode 2
At the positions of 2a, 22b, 23a, and 23b, polarization processing is performed in the thickness direction as indicated by arrows, and the input electrode 2
Between the output electrodes 2a, 22b, 23a, and 23b and the output electrodes 25, polarization processing is performed in the longitudinal direction as indicated by arrows.

[0006] This third-order Rosen-type piezoelectric transformer 20 comprises:
There are three points of vibration nodes, one on each side and the center.
Since the connection and support of the input / output lead wires can be performed at those portions, there is an advantage that a reduction in efficiency and disconnection of the lead wires can be prevented.

FIG. 6 is a perspective view of a piezoelectric transformer having two output electrodes. In the figure, 30 is a tertiary Rosen type piezoelectric transformer, 32a and 32b are input electrodes provided at the center, and 35 and 36 are output electrodes provided at both sides. At the positions of the input electrodes 32a and 32b, polarization processing is performed in the thickness direction as indicated by arrows, and the input electrodes 32a and 32b are polarized.
Between b and the output electrodes 35 and 36, polarization is performed in the longitudinal direction as shown by arrows.

FIG. 7 shows a driving circuit of the piezoelectric transformer 30 having two output electrodes described in FIG. 8 is a current detection circuit including a diode D, a resistor R, a capacitor C, etc.
7 is an input source on the primary side, and RL is a load such as a cold cathode tube.

The input electrodes 32a and 32b on the primary side on the front and back sides
During this time, an AC voltage from the input source 7 is applied, and the output electrodes 35,
A high-frequency high-frequency voltage is applied to a load RL such as a secondary-side cold-cathode tube connected between the light-emitting elements 36 to turn on and drive the load RL. This load RL is floating from the ground.

The output electrode 36 of the load RL is connected to the ground via the resistor R because the current detection circuit 8 is connected to the output electrode 36. The current detection circuit 8 detects a load current flowing through the load RL and outputs a detection signal to a next stage (not shown).
To send to. The input current is controlled based on the output from the next stage to keep the load current constant.

[0011]

However, in this drive circuit, the load RL is directly connected to the ground which is one end of the input source 7 via the current detection circuit 8. For this reason, the stray capacitance of the load RL is large, and a large leakage current occurs at the load RL. This leakage current will be described with reference to FIG. FIG. 8 is an explanatory diagram of leakage current in a conventional piezoelectric transformer drive circuit. One end of the load RL is connected to an output electrode 35 and an output electrode 36 of a high voltage output (for example, 2 HV).
The output electrode 36 is connected to the ground via the resistor R of the current detection circuit 8. For this reason, the leakage current i ₂ is generated via the stray capacitance C _S and the output terminal 35.
And between the ground. Due to the stray capacitance C _{S, the} higher the frequency and the higher the output voltage, the greater the leakage current i ₂ . If the load RL is a cold-cathode tube, the brightness is reduced accordingly. Therefore, there is a problem that the frequency for obtaining a sufficient voltage is limited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and completely isolates the circuits on the primary and secondary sides of the piezoelectric transformer to minimize the stray capacitance at the load, thereby reducing the leakage at the load. An object of the present invention is to provide a tertiary Rosen-type piezoelectric transformer capable of applying a stable high-frequency high-frequency voltage to a load with a reduced current, and a drive circuit therefor.

[0013]

The tertiary Rosen-type piezoelectric transformer of the present invention is provided with two sets of input electrodes and two sets of output electrodes, and the input electrodes of each set are insulated from each other. Therefore, 1
It has a structure in which two sets of piezoelectric transformers, each having a set of input electrodes and one output electrode and having uniform characteristics, are combined. The output from the output electrode is balanced and the load is floating above ground. As a result, the stray capacitance of the load can be significantly reduced. Since the input electrodes of each set are insulated from each other, an external connection between the input electrodes of each set is required, and the function is expanded by the external connection. In addition, since the tertiary Rosen-type piezoelectric transformer has three vibration nodes at both sides and the center, it is possible to connect and support the input / output lead wires at those points. In addition, there is an advantage that the efficiency can be prevented and the lead wire can be prevented from being broken.

The driving circuit of the piezoelectric transformer of the present invention has a circuit configuration using a tertiary Rosen-type piezoelectric transformer provided with two sets of input electrodes and two output electrodes which are insulated from each other. Since the current detection circuit is provided on one of the input electrodes of the tertiary Rosen-type piezoelectric transformer, the ground of the current detection circuit is on the same primary side. Therefore, unlike the case where the current detection circuit is provided in the load as in the related art, there is no large stray capacitance in the load, and a large leakage current can be prevented. In the present invention, since the leakage current is small, when a cold cathode tube is used as the load, the entire cold cathode tube can be lit without luminance unevenness without lowering the luminance.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A tertiary Rosen-type piezoelectric transformer according to the present invention is provided with primary-side input electrodes 2a and 3a on the surface of the central portion, and the position of the rear surface of the central portion corresponding to the input electrodes 2a and 3a. Are provided with input electrodes 2b and 3b, output electrodes 5 and output electrodes 6 on the secondary side are provided on the side of the surface, the central portion is polarized in the thickness direction, and both sides except the central portion are longitudinally oriented. Of the primary side input electrode 2a,
2b and the input electrodes 3a, 3b are insulated and 1
It is characterized in that the positions of the input electrodes 2a, 2b, 3a, 3b on the secondary side and the positions of the output electrodes 5, 6 on the secondary side are node points.

The input electrodes 2a and 3a are formed by diagonal slits extending diagonally, and the input electrodes 2b and 3b are formed by diagonal slits extending diagonally. 2b, 3
A feature is that a part of a and 3b is located at a node position.

Further, the drive circuit for the tertiary Rosen-type piezoelectric transformer of the present invention comprises primary-side input electrodes 2a, 2b, 3 provided on the front and back surfaces of the center of the tertiary Rosen-type piezoelectric transformer 1.
a primary-side input circuit for applying an AC voltage from an input source 7 to a and 3b, and a load between a secondary-side output electrode 5 and an output electrode 6 provided on the side of the surface of the tertiary Rosen-type piezoelectric transformer 1 RL
And a secondary-side output circuit for connecting the primary-side input electrodes 2a,
2b, 3a, 3b, and a current detection circuit 8 for detecting a load current on the secondary side provided on any one of the primary side and the primary side.
It is characterized in that the secondary side is insulated.

[0018]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a piezoelectric transformer used in a cold-cathode tube lighting inverter according to an embodiment of the present invention.
In the figure, 1 is a tertiary Rosen type piezoelectric transformer composed of a substantially rectangular piezoelectric element made of PZT (lead zirconate titanate), 2a, 2b, 3a and 3b are input electrodes provided on the front and back surfaces at the center, Reference numerals 5 and 6 denote output electrodes provided on the side of the surface. Each of these electrodes can be easily formed by printing a silver-based material. These input electrodes 2
a, 3a are formed by diagonal slits extending diagonally, and the input electrodes 2b, 3b are also formed by diagonal slits extending diagonally. That is, the input electrodes 2a, 2b and the input electrodes 3a, 3b are divided by diagonal slits so as to be located on nodes indicated by broken lines in the figure, and are insulated from each other. By dividing the electrode by this oblique slit, the input electrode and the node position become the same.

At the positions of the input electrodes 2a, 2b, 3a and 3b, polarization is performed in the thickness direction as indicated by arrows, and at other portions, polarization is performed in the same longitudinal direction as indicated by arrows. ing. Therefore, the output electrodes 5 and 6 output balanced voltages of opposite polarities. In the case of the tertiary Rosen type, the polarization process becomes easier because the distance between the input and output electrodes is shorter than that of the secondary Rosen type shown in FIG.

In the tertiary Rosen-type piezoelectric transformer 1, since the vibration node points are located at three places on both sides and the center,
Since connection and support of the input and output lead wires can be performed at those portions, there is an advantage that efficiency reduction and disconnection of the lead wire can be prevented. Moreover, the input electrode 2a
And 3a and 2a and 3b are divided by diagonal slits extending diagonally, so that each input electrode 2a, 2a
Some of b, 3a and 3b are at the mead position. By connecting the lead wire to the position of this node, the connection point of the lead wire does not vibrate, and disconnection can be prevented. In addition, load RL is applied to the balanced output from output electrodes 5 and 6.
Is connected, the output side is in a state of floating from the ground, so that the stray capacitance of the load can be greatly reduced, and the leakage current can be greatly reduced.

FIG. 2 shows a driving circuit of the piezoelectric transformer used in the cold cathode tube lighting inverter according to the embodiment of the present invention. In the figure, reference numeral 1 denotes the third-order Rosen type piezoelectric transformer shown in FIG. 1, R2a, R2b, R3a and R3b are resistors,
Is a primary side AC input source, RL is a load such as a cold cathode tube, io is a load current flowing through the load, and 8 is a current detection circuit for detecting a load current composed of a resistor R2a, a capacitor C and a diode D. . Note that resistors R2a, R3a, R3b are connected to the input electrodes 2a, 3a, 3b in order to balance the resistance R2b for load current detection provided on the input electrode 2b.

Next, the operation will be described. A voltage at the resonance frequency of the tertiary Rosen-type piezoelectric transformer 1 is applied from the input source 7 to the input electrodes 2a and 2b via the resistors R2a and R2b. At the same time, the input electrodes 3a, 3a are connected via the resistors R3a and R3b.
3b is also applied. The voltage applied to the input electrodes 2a and 2b is output from the output electrode 5 as a high voltage of a boosted resonance frequency, and the voltage applied to the input electrodes 3a and 3b is a high voltage of a boosted resonance frequency of the opposite polarity. Output electrode 6
Output from Therefore, the output electrodes 5 and 6 are connected to the load RL.
From which a balanced high voltage is applied.

The load current io is, as shown in the figure, the path of output electrode 5 → load RL → output electrode 6 → input electrode 3a → resistance R3a → resistance R2a → input electrode 2a → output electrode 5 and output electrode 5 → It flows through two paths: load RL → output electrode 6 → input electrode 3b → resistance R3b → resistance R2b → input electrode 2b → output electrode 5. Therefore, the third-order Rosen-type piezoelectric transformer 1
Can be considered as the input electrodes 2a, 2b, 3a, and 3b.

The current detecting circuit 8 rectifies and smoothes the voltage drop caused by the half load current io flowing through the resistor R2b by the diode D and the capacitor C, and sends it to the next stage (not shown). The frequency of the input source 7 is controlled based on the output from the current detection circuit 8 so that the load current is constant.

By providing the current circuit 8 on the input electrode 2b using the tertiary Rosen type piezoelectric transformer 1, the primary side and the secondary side can be completely insulated and separated. Since the stray capacitance of the load RL can be significantly reduced and the leakage current can be minimized, a high-frequency high frequency can be applied to the load in a stable state.

FIG. 3 is an explanatory diagram of leakage current in the driving circuit of the piezoelectric transformer according to the present invention. The output of the tertiary Rosen-type piezoelectric transformer 1 from the output electrodes 5 and 6 is a balanced output and floats from the ground. For this reason,
Stray capacitance of the load RL becomes the form of stray capacitance C _S of the pair over scan is connected to the two positions in series, a half of the stray capacitance C _S. The resulting leakage current i ₁ is half of the conventional stray capacitance shown in FIG. 8, so that the leakage current is also halved, enabling driving using a higher frequency than the conventional driving circuit.

[0027]

As described above, the tertiary Rosen-type piezoelectric transformer according to the present invention is provided with the primary-side input electrodes 2a and 3a on the surface of the central portion, and the central portion corresponding to the input electrodes 2a and 3a. Input electrodes 2b and 3b are provided at the positions on the back surface of the substrate, output electrodes 5 and output electrodes 6 on the secondary side are provided on the side of the front surface, the central portion is polarized in the thickness direction, and both sides except the central portion are provided. Treatment polarization in the same longitudinal direction,
The input electrodes 2a, 2b on the secondary side are insulated from the input electrodes 3a, 3b and the input electrodes 2a, 2b, 3
Since the positions of a and 3b and the positions of the output electrodes 5 and 6 on the secondary side are node points, it is possible to connect and support the input / output lead wires at those portions, thereby lowering the efficiency and reducing the lead. There is an effect that disconnection of the wire can be prevented.

In the tertiary Rosen-type piezoelectric transformer of the present invention, the input source 7 supplies the primary-side input electrodes 2a, 2b, 3a, 3b provided on the front and back surfaces of the center of the tertiary Rosen-type piezoelectric transformer 1. Primary-side input circuit for applying the AC voltage of
A load RL is connected between an output electrode 5 on the secondary side and an output electrode 6 provided on the side of the surface of the next Rosen-type piezoelectric transformer 1.
A secondary-side output circuit and primary-side input electrodes 2a, 2b, 3a,
3b, and a current detection circuit 8 for detecting a load current on the secondary side provided on any one of the primary side 3b. Since the primary side and the primary side are insulated, the stray capacitance of the load is greatly reduced. As the leakage current is reduced, stable driving at a higher frequency is enabled.

[Brief description of the drawings]

FIG. 1 is a perspective view of a third-order Rosen-type piezoelectric transformer according to an embodiment of the present invention.

FIG. 2 is a drive circuit diagram of a piezoelectric transformer according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a leakage current in a drive circuit for a piezoelectric transformer according to the present invention.

FIG. 4 is a perspective view of a secondary Rosen-type piezoelectric transformer in a conventional example.

FIG. 5 is a perspective view of a third-order Rosen-type piezoelectric transformer in a conventional example.

FIG. 6 is a perspective view of a tertiary Rosen-type piezoelectric transformer having two output electrodes.

FIG. 7 is a driving circuit of a piezoelectric transformer in a conventional example.

FIG. 8 is an explanatory diagram of leakage current in a conventional piezoelectric transformer drive circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Tertiary Rosen type piezoelectric transformer 2a, 2b, 3a, 3b Input electrode 5, 6 Output electrode 7 Input source 8 Current detection circuit 10 Secondary Rosen type piezoelectric transformer 12a, 12b Input electrode 15 Output electrode 20 Tertiary Rosen type piezoelectric transformer 22a, 22b, 23a, 23b input electrode 25 the output electrode 30 cubic Rosen-type piezoelectric transformer 32a, 32b input electrodes 35 and 36 output electrode C capacitor C _S stray capacitance D diode io load current i ₁ leakage current i ₂ leakage current R resistor R2a, R2b, R3a, R3b Resistance RL Load

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Akira Mizutani 5-5-30 Chiyoda, Sakado-shi, Saitama Pref.

Claims (3)

[Claims] An input electrode (2) on a primary side is provided on a surface of a central portion.
a, 3a), input electrodes (2b, 3b) are provided at the central back surface corresponding to the input electrodes (2a, 3a), and a secondary output electrode (5) is provided on the side of the front surface. Output electrode (6)
The central portion is polarized in the thickness direction, and both sides except the central portion are polarized in the same direction in the longitudinal direction. The primary input electrodes (2a, 2b) and the input electrodes (3a, 3
b) and the input electrode (2
a, 2b, 3a, 3b) and the position of the secondary output electrodes (5, 6) are node points.
Next Rosen type piezoelectric transformer. 2. The input electrodes (2a, 3a) are divided by diagonal slits extending diagonally, and the input electrodes (2b, 3b) are divided by diagonal slits extending diagonally. 3. A tertiary Rosen-type piezoelectric transformer according to claim 1, wherein a part of the input electrodes (2a, 2b, 3a, 3b) is located at a node. 3. A primary input electrode (2a, 2b, 3a, 3b) provided on the front and back surfaces of a central part of the tertiary Rosen type piezoelectric transformer (1) according to claim 1 or 2.
, A primary-side input circuit for applying an AC voltage from an input source (7), a secondary-side output electrode (5) provided on a side portion of the surface of the tertiary Rosen-type piezoelectric transformer (1), and an output electrode ( 6) A secondary-side output circuit for connecting a load (RL) therebetween, and a secondary-side load current provided on any one of the primary-side input electrodes (2a, 2b, 3a, 3b) is detected. A drive circuit for a tertiary Rosen-type piezoelectric transformer, comprising a current detection circuit (8), wherein the primary side and the secondary side are insulated.