DE20209308U1 - Piezoelectric ceramic transistor - Google Patents

Description

P14363 W/DP/cho
Shin Jiuh Corp.

PIEZOELECTRIC CERAMIC TRANSISTOR

Field of the invention

The present invention relates to a piezoelectric ceramic transistor. More particularly, the present invention provides an electric element suitable for use in a piezoelectric conversion device and capable of increasing electric performance.

Background of the invention

As shown in the schematic views of FIG. 1 and FIG. 2, current driving devices for driving cold cathode fluorescent lamps (CCFLs) comprise a driving device and a CCFL driven by the driving device. The driving device comprises a power supply unit 1, a pulse width modulation (PWM) control unit 2, a driving unit 3 and a piezoelectric ceramic voltage transformer 4'. The CCFL 7 is connected to the PWM 2 through a current feedback 5, and the piezoelectric ceramic voltage transformer 4' is connected to the PWM 2 through a voltage feedback 6. When this driving device is turned on and inputs a voltage, the driving unit 3 immediately drives the piezoelectric ceramic voltage transformer 4', which in turn drives the lighting of the CCFL 7 through the piezoelectric ceramic reversal effect. The PWM control unit 2 then detects the average output current intensity of the CCFL 7 through the current feedback 5 to output a resonance frequency. The resonance frequency via the control unit 3 and the piezoelectric ceramic voltage transformer 4' can control the average current of the CCFL 7. Thus, the light source generated by the CCFL 7 is projected onto the semi-transparent back panel to illuminate the back panel and fit the display frame of the LCD screen. Since the illumination of the CCFL 7 is limited or uniform by driving the above-mentioned driving means, therefore, several

CCFL 7 is required to achieve uniform back panel illumination of the LCD screen. As a result, the manufacturing cost is increased and the manufacturing process is not easy to carry out.

Summary of the invention

It is therefore an object of the invention to provide a piezoelectric ceramic transistor which solves the above problems by comprising a single-layer or stacked multilayer piezoelectric ceramic voltage transformer having an input terminal connected in series with a capacitor. The capacitor thereby forms a bypass capacitor which increases the power and prevents loss due to feedback, so that vibrations of the piezoelectric ceramic voltage transformer are compensated. Alternatively, the above connection scheme is achieved either by serially connecting a capacitor between a power output of the transformer and a load terminal or by parallelly connecting a first capacitor to a power input of the transformer and a second capacitor in series between a power output of the transformer and the load terminal to achieve increased power and thereby increase the load current.

Another object of the invention is to provide a piezoelectric ceramic transistor which is formed in a single element either by the connection of conventionally known electrical elements or by semiconductor packages.

Moreover, another object of the invention is to provide a piezoelectric ceramic transistor which reduces the number of CCFLs attached to an LCD panel, thereby facilitating manufacture and reducing manufacturing costs.

Yet another object of the present invention is to provide a piezoelectric ceramic transistor which can enable CCFL with higher power or longer length or driving a CCFL with lower driving voltage.

To provide a further understanding of the invention, the following detailed description illustrates embodiments and examples of the invention, this detailed description being intended only to illustrate the invention.

Short description of the drawings

The drawings included herein provide a further understanding of the invention. A brief introduction to the drawings is as follows:

FIG.1 is a block diagram illustrating a driving circuit of the backlight source of an LCD panel;

FIG. 2 illustrates a corresponding circuit of the block diagram according to FIG. 1;

FIG.3 is a block diagram of a realized circuit according to an embodiment of the present invention;

FIG. 4 is a circuit diagram corresponding to the block diagram of FIG. 3;

FIG.5 is a block diagram illustrating another embodiment of the present invention;

FIG.6 is a block diagram illustrating still another embodiment of the present invention.

Detailed description of the implementation examples

Wherever possible in the following description, like reference characters refer to like elements and parts unless otherwise specified.

With reference to FIG. 3 and FIG. 4, two block diagrams schematically illustrate a realized circuit according to an embodiment of the present invention. As illustrated, the piezoelectric ceramic transistor of the invention is essentially

by serially connecting a capacitor to an input terminal of a single-layer or stacked multilayer piezoelectric ceramic voltage transformer (piezoelectric film). An LCD screen driving device is illustrated as an example of an embodiment of the invention. This driving device comprises a power supply unit 1, a pulse width modulation (PWM) control unit 2, a driving unit 3 and a piezoelectric ceramic transistor 4. As constructed above, the driving device is used to drive a cold cathode fluorescent lamp (CCFL) 7 which produces a light source for the back light of the LCD. The power supply unit 1 provides the power required for the operation of all the units of the driving device.

The PWM control unit 4 is connected to an input terminal of the driver unit 3 and receives a current feedback 5 from the CCFL 7 and a voltage feedback 6 from the piezoelectric ceramic transistor 4, respectively. From the current feedback 5 and according to the average current intensity detected from the output of the CCFL 7, the PWM control unit 4 appropriately controls the average current of the CCFL 7.

The driver unit 3 has an input connected to the PWM control unit 2 and receives a resonance frequency output from the PWM control unit 2.

The piezoelectric ceramic transistor 4 is formed by a capacitor 42 connected in parallel to an input terminal of a piezoelectric ceramic transformer 41. The capacitor 42 thus forms a bypass capacitor which enables higher performance to be achieved. The capacitor 42 can prevent losses due to feedback and contributes to compensating for vibration of the piezoelectric ceramic transformer 41.

When the driver device is turned on, the driver unit 3 immediately drives the piezoelectric ceramic transistor 4, which in turn drives the CCFL 7 for lighting operation. At this moment, the PWM control unit 2 measures the average current intensity output from the CCFL 7 through the current feedback and outputs a resonance frequency. The resonance frequency is fed to the driver unit 3 and the

piezoelectric ceramic transistor 4 to control the average current of the CCFL.

The examples of connecting the capacitor to the single-layer or stacked multilayer piezoelectric ceramic transformer are illustrated below.

1. Single layer piezoelectric ceramic transformer

A. Test conditions: 1.V(DCV): 14V ±5%

2. Load: Lamp length 220 mm

3. Working frequency: 66 KHz ± 2 KHz

4. Light regulation conditions: DCV OV

5. Single layer piezoelectric ceramic transformer: 48mm Lx8mm Wx 1.8mm T

6. Static capacitance of low voltage terminal: 1.25 nF

7. Number of layers of input port: 1 layer

8. Test temperature: 27°C ± 10%

B. Test results:

Without capacitor: Tube voltage (RMS) acV: 30 V; Tube current (AVG) mAacI: 0 mA;

With capacitor: Tube voltage (RMS) acV: 567 V; Tube current (AVG) mAacI: 6.729 mA.

C. Test efficiency:

1. Without capacitor

Tube voltage (RMS)acV x Tube current (AVG)mAacI = P_out(w) 30VxOmA = OW Input voltage (DCV) x Input current (DCI) = P_IN 14 V x 0.036 A = 0.5 W

2. With parallel capacitor

Tube voltage (RMS) acV x Tube current (AVG) mA acI = P_out(w) 576 V x 0.6729 mA = 3.81 W Input voltage (DCV) x Input current (DCI) = P_IN 14V x 1.268 A = 17.72 W

As shown in the above test results, the addition of the capacitor of 0.127 μΩ can turn on the single-layer piezoelectric ceramic transformer. The problem associated with the need to use a step-up transformer first to step up the voltage before driving the single-layer piezoelectric ceramic transformer can be improved. The manufacturing process can thus be facilitated and the manufacturing cost is reduced.

II. Stacked multilayer piezoelectric ceramic transformer

A. Test conditions: 1.V(DCV): 12V ±5%

2. Load: Lamp length 220 mm

3. Working frequency: 73.39 KHz ± 2 KHz

4. Light regulation conditions: DCV OV

5. Stacked multilayer piezoelectric ceramic transformer ± 10%: 48mmLx8mmWxl,8mm T

6. Static capacitance at low voltage terminal: 82.9 nF

7. Number of layers of input port: 18 layers

8. Test temperature: 27 ⁰ C ± 10 %

B. Test results:

Without capacitor: Tube voltage (RMS) acV: 500 V; Tube current (AVG) mAacI: 6.86 mA;

With capacitor: Tube voltage (RMS) acV: 475 V; Tube current (AVG) mAacI: 13.186 mA.

C. Test efficiency:

1. Without capacitor

Tube voltage (RMS)acV x Tube current (AVG)mAacI = P_out(w) 500 V x 6.86 mA = 3.43 W Input voltage (DCV) x Input current (DCI) = P_IN 12 V x 0.378 A = 4.53 W

2. With parallel capacitor

Tube voltage (RMS)acV x Tube current(AVG)mAacI = P_out(w) 475 V x 13.186 mA = 6.25 W Input voltage (DCV) x Input current (DCI) = P_IN

·

·

12V x 0.882A-10.58W

As shown in the above test results, the addition of the 0.1 μΩ capacitor can turn on the stacked multilayer piezoelectric ceramic transformer.

FIG. 5 illustrates another embodiment of the invention. As illustrated, besides connecting the capacitor 42 in parallel to the input terminal of the transformer 41, it can also be envisaged to connect a capacitor 42' in series between the output terminal of the transformer 41 and the load (CCFL) 7 to increase the output voltage and thereby increase the power.

FIG. 6 illustrates yet another alternative embodiment of the invention. As shown, the capacitor 42 may be connected in parallel with the input terminal of the transformer 41, while it may also be connected in series between the output terminal of the transformer 41 and the load (CCFL) 7 to increase the output voltage and thereby increase the power.

The following results compare a schematic connection in which the piezoelectric ceramic voltage transformer is not connected to any capacitor, and connection schemes in which a capacitor is connected in series between the output terminal and the load terminal, or several capacitors are simultaneously connected in parallel and in series between the input terminal and the output terminal of the piezoelectric ceramic voltage transformer:

A. Test conditions:
1.V(DCV): 12.1V ±5%

2. Load: Lamp length 220 mm x 1 unit

3. Working frequency: 74 KHz ± 2 KHz

4. Light regulation conditions: DCV OV

5. Single layer piezoelectric ceramic transformer: 42 mm L x 7.4 mm W x 3.7 mm T

6. Static capacitance of low voltage terminal: 185 nF

7. Number of layers of input port: 18 layers

8. Test temperature: 27°C ± 10%

9. Capacitances: lOOpF, 68nF
B. Test results:

Without capacitance: Tube current (AVG) mAacI: 7.21 mA;

With a capacitor of 100pF connected in series to the output terminal: Tube current (AVG) mAacI: 8.25 mA.

With a capacitor of 100pF connected in series to the output terminal and a capacitor of 68nF connected in parallel to the input terminal: Tube current (AVG) mAacI: 10.83 mA.

From the above results, it can be observed that the output lamp current can be increased either by serially connecting a capacitor to the output terminal of the transformer or by serially connecting a first capacitor to the output of the transformer and simultaneously connecting a second capacitor in parallel to the input terminal of the transformer.

The invention as described above is advantageous in that it enables the reduction of the number of lamps 7 attached to the LCD panel. Alternatively, with respect to the same conditions of input and load, the corresponding input voltage of the driving device can also be reduced. Thereby, the number of electrical components can also be reduced. By further reducing the volume and the number of layers of the piezoelectric transformer, the manufacturing cost is reduced and the manufacturing process is simplified.

Moreover, the invention is also advantageous in enabling a single piezoelectric ceramic transistor element 4 to be formed from the piezoelectric ceramic transformer 41 and the capacitor 42, 42' via a semiconductor packaging process. Alternatively, the piezoelectric ceramic transformer 41 and the capacitor 42 may be connected via conventional electrical elements.

It should be apparent to those skilled in the art that the above description is only illustrative of certain embodiments and examples of the invention. The invention is therefore intended

»·· « »t Il ·· P

half various modifications and variations which may be made in the structure and conditions of the invention described herein, provided that they fall within the scope of the invention as defined in the following appended claims.

Claims (6)

1. A piezoelectric ceramic transistor ( 4 ) suitable for use in a piezoelectric transducer device, which comprises a piezoelectric ceramic voltage transformer ( 41 ) and a capacitor ( 42 ), wherein the capacitor ( 42 ) is connected in parallel to an input terminal of the piezoelectric ceramic voltage transformer ( 41 ) to form a bypass capacitor, whereby the performance can be increased and the loss due to feedback can be prevented so that vibrations of the piezoelectric ceramic voltage transformer ( 41 ) can be compensated. 2. A transistor according to claim 1, wherein the piezoelectric ceramic voltage transformer ( 41 ) and the capacitor ( 42 ) are connected to each other via conventional electrical elements to form a piezoelectric ceramic transistor with enhanced performance. 3. The transistor of claim 1, wherein the piezoelectric ceramic voltage transformer ( 41 ) and the capacitor ( 42 ) are fabricated via semiconductor packaging to form a single piezoelectric ceramic transistor. 4. Transistor according to claim 1, wherein the piezoelectric ceramic transistor can supply either a cold cathode fluorescent lamp (CCFL) ( 7 ) with a higher driving power or a CCFL of a longer length. 5. Piezoelectric ceramic transistor ( 4 ) suitable for use in a piezoelectric transducer device, which has a piezoelectric ceramic voltage transformer ( 41 ) and a capacitor ( 42 ), wherein the capacitor ( 42 ) is connected in series between an output terminal of the piezoelectric ceramic voltage transformer ( 41 ) and a load terminal, whereby an output voltage can be increased and the power can be increased. 6. Piezoelectric ceramic transistor ( 4 ) suitable for use in a piezoelectric converter device, which has a piezoelectric ceramic voltage transformer ( 41 ) and at least a first and a second capacitor ( 42 , 42 '), wherein the first capacitor ( 42 ) is connected in parallel to an input terminal of the piezoelectric ceramic voltage transformer ( 41 ) and between an output terminal of the piezoelectric ceramic voltage transformer ( 41 ) and a load terminal ( 7 ) so that a bypass capacitor is formed for increasing the power and preventing a loss due to feedback, whereby vibrations of the piezoelectric ceramic voltage transformer ( 41 ) can be compensated; while the second capacitor ( 42 ') is connected in series between the output terminal of the piezoelectric ceramic voltage transformer ( 41 ) and the load terminal, whereby an output voltage and the power can be increased respectively.