JPH10321928A - Piezoelectric transducer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent inflow of a primary side current to a secondary side when a surrounding temperature is increased or the secondary side is open or short- circuited, by method wherein a positive characteristic thermistor connecting in series to the primary side of a piezoelectric transducer element is provided. SOLUTION: A positive characteristic thermistor element 33 is in series connected to a primary side of a piezoelectric transducer element 6, and further to a power supply 2. If a temperature is increased, a resistance value is increased in characteristics of the positive characteristic thermistor element 22. If a voltage of a half-wave sine wave is inputted from a power supply 2 to the primary side of the piezoelectric transducer element 6 via the positive characteristic thermistor element 33, an output voltage is caused between an output electrode 13 and a common electrode on a secondary side. If the surrounding temperature of the piezoelectric transducer element 6 is increased, primary side impedance thereof is decreased, but the resistance value of the positive characteristic thermistor element 33 is increased, so that the increase in a primary side current i is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer device, and more particularly to a piezoelectric transformer device used in a high-voltage power supply circuit such as a backlight inverter for a liquid crystal display, a fluorescent lamp lighting inverter, and a copying machine.

[0002]

2. Description of the Related Art As this kind of piezoelectric transformer device, there is conventionally known a piezoelectric transformer device shown in FIG. The piezoelectric transformer device 85 generally includes a piezoelectric transformer element 83 and a power supply 80 connected to the primary side of the piezoelectric transformer element 83. A load resistor 84 is connected to the secondary side of the piezoelectric transformer element 83. When a half-wave sinusoidal input voltage is applied from the power supply 80 to the primary side of the piezoelectric transformer element 83, strong mechanical vibration occurs in the piezoelectric transformer element 83 in the longitudinal direction, and an alternating current is applied to the secondary side of the piezoelectric transformer element 83. A voltage is generated.

[0003]

When the ambient temperature (including self-heating) of the piezoelectric transformer element 83 rises, the capacitance of the piezoelectric transformer element 83 increases, the primary impedance decreases, and the primary side impedance decreases. The current i increases. This phenomenon proceeds even if the output of the secondary side of the piezoelectric transformer element 83 is saturated, so that the piezoelectric transformer element 83 further generates heat, and there is a fear that the thermal runaway may finally occur.

[0004] As shown in FIG. 8, the resistance value of a load resistor 84 connected to the secondary side of the piezoelectric transformer element 83 is ∞.
(The secondary side is open) or the resistance value of the load resistor 84 is 0.
In the case of (secondary short-circuit), the primary impedance at the resonance frequency becomes extremely small. Therefore, at this time, when the piezoelectric transformer element 83 is driven near the natural resonance frequency, a large primary current i flows into the piezoelectric transformer element 83, and there is a problem that the piezoelectric transformer element 83 is damaged. Was.

Accordingly, an object of the present invention is to provide a piezoelectric transformer device in which a large primary current does not flow into the piezoelectric transformer element even when the ambient temperature rises or the secondary side of the piezoelectric transformer element is opened or short-circuited. It is in.

[0006]

In order to achieve the above object, a piezoelectric transformer device according to the present invention comprises a piezoelectric transformer element and a PTC thermistor element connected in series to the primary side of the piezoelectric transformer element. And characterized in that: Here, as the piezoelectric transformer element, a Rosen type piezoelectric transformer element is desirable. The positive characteristic thermistor element is
When the temperature is low (for example, normal temperature), the resistance value becomes small. Therefore, energy loss at room temperature, which does not require resistance, is reduced.

With the above configuration, even if the ambient temperature rises or the secondary side of the piezoelectric transformer element is opened or short-circuited,
A positive temperature coefficient thermistor element connected in series to the primary side of the piezoelectric transformer element suppresses an increase in the primary side current.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the piezoelectric transformer device according to the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, a piezoelectric transformer device 31
Generally comprises a piezoelectric transformer element 6, a power supply 2 connected to the primary side of the piezoelectric transformer element 6, and a PTC thermistor element 3 connected in series to the primary side of the piezoelectric transformer element 6.
3 is comprised.

The piezoelectric transformer element 6 is, for example, shown in FIGS.
As shown in FIG. 2, a Rosen-type piezoelectric transformer element having a laminated structure is shown. This Rosen-type piezoelectric transformer element 6 has 195
In 6 years, the US C.I. A. This is a piezoelectric transformer element with a structure announced by Rosen. Hereinafter, the Rosen-type piezoelectric transformer element will be specifically described. The Rosen-type piezoelectric transformer element 6 is formed by manufacturing a ceramic green sheet 15 such as lead zirconate titanate (PZT) by a doctor blade method, and forming internal electrodes 16a and 16b on the green sheet 15 by screen printing or the like. The green sheet 15 is laminated and pressed and sintered.

Next, after the sintered laminate is cut and polished, input electrodes 11 are provided on the upper surface and the near end surface of the piezoelectric transformer element 6 in the substantially left half in FIG. Are provided with a common electrode (ground electrode) 12, and an output electrode 13 is provided on the right end face. These electrodes 11 to
13 is provided by a method such as silver printing. The input electrode 11 is electrically connected to the internal electrode 16b,
2 is electrically connected to the internal electrode 16a.

Next, a predetermined bias voltage is applied to the electrodes 11 to 13, and as shown in FIGS. 3 and 4, the input portion in the substantially left half of the piezoelectric transformer element 6 is in a direction parallel to the stacking direction. The polarization process is performed on the output portion of the substantially right half in the direction perpendicular to the stacking direction. 3 and 4, the direction of the arrow indicates the direction of polarization.

In this piezoelectric transformer element 6, when an AC voltage having a frequency substantially equal to the natural resonance frequency in the longitudinal direction of the piezoelectric transformer element 6 is applied between the input electrode 11 and the common electrode 12, the piezoelectric transformer element 6 In this case, strong mechanical vibration occurs in the longitudinal direction, whereby electric charges are generated at the output portion by a piezoelectric effect, and an output voltage is generated between the output electrode 13 and the common electrode 12. In particular, the laminated piezoelectric transformer element 6
Has a large step-up ratio, and can respond to a low input voltage. Further, the output electrode 13 of the piezoelectric transformer element 6
Is connected to one end of a load such as a cathode tube, and the other end of the load is connected to the common electrode 12.

The PTC thermistor element 33 is connected in series to the primary side of the piezoelectric transformer element 6. As shown by a solid line 41 in FIG.
It has the property that the resistance value rises as the temperature rises. Accordingly, the piezoelectric transformer device 31 including the positive temperature coefficient thermistor element 33 requires a resistor when the ambient temperature is low (for example, normal temperature) and a large current does not flow through the primary side of the piezoelectric transformer element 6, that is, a resistor is required. Otherwise, since the resistance value of the positive temperature coefficient thermistor element 33 is small, energy loss can be reduced as compared with a resistance element having a constant resistance value (see a dotted line 42 in FIG. 5).

Next, the operation and effect of the piezoelectric transformer device 31 having the above configuration will be described. A half-wave sinusoidal input voltage is applied from the power supply 2 to the primary side of the piezoelectric transformer element 6 via the positive characteristic thermistor element 33. The repetition frequency of the half-wave sine wave is set near the natural resonance frequency of the piezoelectric transformer element 6 in the longitudinal direction. When a voltage is applied to the input portion of the piezoelectric transformer element 6, strong mechanical vibration occurs in the piezoelectric transformer element 6 in the longitudinal direction, and charges are generated at the output section by the piezoelectric effect. Then, an AC voltage (output voltage) is generated between the output electrode 13 of the piezoelectric transformer element 6 and the common electrode 12.

When the ambient temperature (including self-heating) of the piezoelectric transformer element 6 rises with the driving of the piezoelectric transformer device 31, the capacity of the piezoelectric transformer element 6 increases and the primary impedance of the piezoelectric transformer element 6 decreases. Lower. However, since the positive-characteristic thermistor element 33 connected in series to the primary side of the piezoelectric transformer element 6 suppresses an increase in the primary side current i, the primary side current i does not increase. Therefore, thermal runaway of the piezoelectric transformer element 6 can be suppressed, and the piezoelectric transformer device 31 can be driven stably. Similarly, even if the secondary side of the piezoelectric transformer element 6 is opened or short-circuited and the primary side impedance at the resonance frequency becomes extremely small, the positive characteristic thermistor element 33 suppresses the increase of the primary side current i. The secondary current i does not increase. Therefore, breakage of the piezoelectric transformer element 6 can be prevented.

This will be described more specifically. FIG. 6 shows a piezoelectric transformer element 6 having a length of 30 mm, a thickness of 1.9 mm,
The width is 6 mm, and the internal electrodes 16a and 16b
Using a Rosen type piezoelectric transformer element having a laminated structure of layers, the resistance value of the positive temperature coefficient thermistor element 33 at 60 ° C. is set to 1Ω, and when the secondary side of the piezoelectric transformer element 6 is short-circuited, the piezoelectric temperature is 60 ° C. 6 shows an input voltage waveform (see a solid line 21 in FIG. 6A) and an output voltage waveform (see a solid line 22 in FIG. 6B) of the transformer element 6. For comparison, an input voltage waveform (see a dotted line 23 in FIG. 6A) and an output voltage waveform (see a dotted line 24 in FIG. 6B) of the piezoelectric transformer element of the conventional piezoelectric transformer device are also shown. I have. From FIG. 6, it is recognized that the distortion of the input and output voltage waveforms of the piezoelectric transformer element 6 of the first embodiment is smaller than in the related art. In addition, when the piezoelectric transformer device was continuously driven, no abnormality occurred in the piezoelectric transformer element 6 of the present embodiment, but the piezoelectric transformer element of the conventional piezoelectric transformer device was damaged.

The piezoelectric transformer device according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In particular, in the piezoelectric transformer element 6 of the above-described embodiment, the electrode 12 is used as a common electrode. However, the present invention is not limited to this. The electrode 11 may be used as a common electrode, and the electrode 12 may be used as an input electrode. Further, a piezoelectric transformer element in which the polarization direction of the output portion on the right half of the piezoelectric transformer element 6 is reversed. Further, the piezoelectric transformer element is not limited to the one having a laminated structure, and may be a single-plate Rosen-type piezoelectric transformer element or a piezoelectric transformer element in which input and output electrodes are independent from each other.

[0019]

As is apparent from the above description, according to the present invention, since the positive temperature coefficient thermistor element is connected in series to the primary side of the piezoelectric transformer element, the ambient temperature rises and the piezoelectric transformer element Even if the secondary side is opened or short-circuited, the PTC thermistor element can suppress an increase in the primary side current of the piezoelectric transformer element, and can protect the piezoelectric transformer element from thermal runaway or damage.

Further, when the ambient temperature is low, such as room temperature,
When a resistor is not required, the resistance value of the positive temperature coefficient thermistor element is small, so that energy loss at room temperature can be reduced as compared with the case of a resistance element, and an efficient piezoelectric transformer device can be obtained.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing one embodiment of a piezoelectric transformer device according to the present invention.

FIG. 2 is an external perspective view of the piezoelectric transformer element shown in FIG.

FIG. 3 is a structural view seen from III-III in FIG. 2;

FIG. 4 is a structural view seen from IV-IV in FIG. 2;

FIG. 5 is a graph showing resistance value characteristics of the positive temperature coefficient thermistor shown in FIG. 1;

6 is a graph showing an input voltage waveform and an output voltage waveform of the piezoelectric transformer element shown in FIG.

FIG. 7 is an electric circuit diagram showing a conventional piezoelectric transformer device.

FIG. 8 is a graph showing a primary impedance of a piezoelectric transformer element.

[Explanation of symbols]

 31: Piezoelectric transformer device 6: Piezoelectric transformer element 33: Positive characteristic thermistor element

Claims (2)

[Claims] 1. A piezoelectric transformer device comprising: a piezoelectric transformer element; and a PTC thermistor element connected in series to a primary side of the piezoelectric transformer element. 2. The piezoelectric transformer device according to claim 1, wherein said piezoelectric transformer element is a Rosen type piezoelectric transformer element.