JPH10326693A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device at a low cost which is equipped with a piezo type transformer and which can light a hot cathode-ray tube stably. SOLUTION: A discharge lamp lighting device is equipped with a hot cathode lamp 6, an inverter circuit to convert a DC voltage E into a high frequency AC voltage, and a piezo type transformer 2b which transforms a high frequency voltage output of the inverter circuit and supplies it to the lamp 6. When the lamp 6 is on, the transformer 2b is driven at a frequency over the serial resonance frequency where the phase nullifies approximately and below f50k where the absolute |Zo| of the output impedance becomes approx. 50 kΩ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a discharge lamp lighting device, and more particularly, to a discharge lamp lighting device using a piezoelectric transformer.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric transformer has the following characteristics (1) to (3) as compared with a general electromagnetic transformer, and application research to electronic equipment utilizing the characteristics has been conducted. Have been done. (1) Since the energy density is high, downsizing can be achieved. (2) Non-combustibility can be achieved. (3) No noise is generated by electromagnetic induction.

A discharge lamp lighting device has been applied to a cold cathode tube lighting of a liquid crystal backlight. Part 1
Finally, there is the one shown in JP-A-8-45679.
FIG. 14 is a block diagram showing the configuration.

In this configuration, a DC power supply E, an inverter circuit 1 for converting the DC power supply E into a high-frequency voltage, a piezoelectric transformer 2a connected in parallel to an output terminal of the inverter circuit 1, and an output terminal of the piezoelectric transformer 2a are connected. The cold cathode tube 3 is provided, and the inverter circuit 1 is driven near the resonance frequency of the piezoelectric transformer 2a to turn on the cold cathode tube 3. While the cold-cathode tube 3 is turned on, a small current of several mA or less flows through the cold-cathode tube 3.

FIG. 15 is a schematic perspective view of a known piezoelectric transformer 2a called a Rosen type. The piezoelectric transformer 2a has a primary electrode formed on the front and back surfaces on one side, which is substantially half of the longitudinal direction, and a secondary electrode formed on the end surface on the other side. Is applied to generate vibration in the thickness-length direction to induce a voltage on the secondary electrode.

FIG. 16 shows a frequency characteristic diagram of the output impedance and phase of a piezoelectric transformer made of Fuji Ceramics Co., Ltd. (material number C213, width 10 mm × length 40 mm × thickness 1.5 mm). Here, the piezoelectric transformer has a characteristic near the wavelength λ mode resonance,
The point at which the phase becomes substantially zero at Hz is the series resonance frequency fs, and the point at which the phase becomes substantially zero at 71 kHz on the high frequency side is the parallel resonance frequency fp. In addition, it can be seen that the phase difference between the series resonance frequency fs and the parallel resonance frequency fp is approximately 90 °, which is inductive.

[0007]

However, in the above conventional example, the following problems occur.

[0008] The cold cathode tube has a characteristic that the lamp voltage is high and the lamp current is small, and it is possible to sufficiently light the lamp by the structure as shown in the conventional example. Was not considered. Experimentally, when a hot cathode tube (FL10, 10W lamp) is used as a load in the configuration as shown in the conventional example, there is a problem that lighting is impossible and a large stress is applied to the piezoelectric transformer.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a discharge lamp lighting device including a piezoelectric transformer, which is capable of stably lighting a hot cathode tube. It is to provide at low cost.

[0010]

According to the first aspect of the present invention, there is provided a discharge lamp, an inverter circuit for converting a DC voltage to an AC high frequency voltage, and a high frequency of the inverter circuit. A discharge lamp lighting device comprising: a piezoelectric transformer that transforms a voltage output and supplies the voltage to the discharge lamp.
When the discharge lamp is turned on, the piezoelectric transformer has an output impedance absolute value | Z equal to or higher than the series resonance frequency at which the phase becomes substantially zero.
It is characterized by being driven at a frequency f50k or less at which o | becomes approximately 50 kΩ.

According to a second aspect of the present invention, the phase of the piezoelectric transformer at a frequency f50k is approximately 90 °.

According to the third aspect of the present invention, the difference between the series resonance frequency and the frequency f50k is 1 kHz.
z or more.

According to the fourth aspect of the present invention, the piezoelectric transformer has a single-plate shape, and has a primary electrode formed on one of the front and back surfaces that is substantially half in the short direction, and a piezoelectric electrode on the other side. And a secondary electrode formed on the end face.

According to a fifth aspect of the present invention, the piezoelectric transformer is characterized in that the piezoelectric transformer has a structure in which piezoelectric bodies and electrodes are alternately formed in layers.

According to the invention described in claim 6, the discharge lamp is of a hot cathode type. According to the seventh aspect of the present invention, a discharge lamp preheating means is provided.

[0016]

Embodiment

(Embodiment 1) FIG. 1 shows a block diagram of a first embodiment of the present invention, and a piezoelectric transformer 2b used in the present embodiment.
2 is shown in FIG. 2, an equivalent circuit of the piezoelectric transformer 2b is shown in FIG. 3, and a frequency characteristic diagram of the output impedance and the phase in the one-wavelength mode (λ mode) of the piezoelectric transformer 2b is shown in FIG. FIG. 5 shows a characteristic diagram of the lamp current with respect to the output impedance.

As shown in FIG. 2, the piezoelectric transformer 2b is a single-plate-shaped piezoelectric body (for example, 41 mm long × 12 mm wide × 1 thickness).
mm), and has a primary electrode formed on the front and back surfaces on one side and a secondary electrode formed on an end surface on the other side, which is approximately half of the lateral direction (that is, the short direction). The primary electrode portion of the piezoelectric body is polarized in the thickness direction, the primary electrode and the secondary electrode are laterally polarized, and an AC voltage is applied to the primary electrode to generate an electrostriction-piezoelectric effect. To generate an AC voltage.

In general, a piezoelectric transformer is defined as an equivalent circuit including capacitors C1, C2, C3, an inductor L1, and resistors R1, R2, R3 as shown in FIG.
Absolute value of output impedance of piezoelectric transformer | Zo |
Is defined as the impedance seen from the secondary electrode side.
The absolute value | Zo | of the output impedance has a frequency characteristic, and has a sharp resonance characteristic when it matches the mechanical resonance frequency. As shown in FIG. 4, the point at which the phase is substantially zero at the low frequency side 160 kHz and the absolute value | Zo | of the output impedance is the minimum is the series resonance frequency fs, and the high frequency side 172 kHz.
The phase is substantially zero at z, the absolute value of the output impedance | Zo
Is the parallel resonance frequency fp. Also,
It can be seen that the phase difference between the series resonance frequency fs and the parallel resonance frequency fp is approximately 90 ° and inductive, and the frequency width from the series resonance frequency fs to the parallel resonance frequency fp is approximately 12 kHz.

The block configuration shown in FIG.
And autotransformers (hereinafter referred to as transformers) T1 and T2 connected in series to the positive terminal of the DC power supply E, and a field effect transistor (hereinafter, switching) connected to both ends of the DC power supply E via the transformer T1. It is called an element.) S
1, a field effect transistor (hereinafter referred to as a switching element) S2 connected to both ends of the DC power supply E via a transformer T2, a piezoelectric transformer 2b, and a hot cathode lamp 6
(For example, FHL10 manufactured by Matsushita), a current detection circuit 10 that detects a lamp current flowing through a hot cathode lamp (hereinafter, referred to as a hot cathode tube) 6, and a control circuit that alternately turns on and off the switching element S1 and the switching element S2. And 7. Here, the transformers T1 and T2 are formed by winding the drum core in a biphasic manner. The secondary electrodes of the transformers T1 and T2 are connected in series to the primary electrodes of the piezoelectric transformer 2b. One end of a hot cathode tube 6 is connected in series to the electrode. The other end of the hot cathode tube 6 is connected in series to the negative terminal of the DC power supply E via the current detection circuit 10.

In the above configuration, the switching elements S1, S
It was confirmed that when the oscillating frequency of No. 2 was set to around 165 kHz and current was supplied, the hot cathode tube 6 was stably lit. Mechanical damage has occurred in the Rosen type piezoelectric transformer shown in the conventional example, but in the present embodiment, stable operation can be performed without causing mechanical damage. Here, the absolute value of the output impedance of the piezoelectric transformer 2b |
Focusing on Zo | and examining the lighting characteristics of the hot cathode tube 6 with frequency characteristics as shown in FIG. 4, the stable lighting frequency range of the hot cathode tube 6 is from the series resonance frequency fs to the parallel resonance frequency fs.
It can be seen that this is the case where the frequency band has inductive properties up to p and the absolute value | Zo | of the output impedance is 50 kΩ or less. That is, as shown in FIG.
When o |> 50 kΩ, the lamp current of the hot-cathode tube 6 becomes substantially zero and the lamp is not lit, and the absolute value | Zo |
The lamp current increases as the resistance decreases from 0 kΩ, and the hot cathode tube 6 is turned on.

From the above, the reason why the hot cathode tube is stably lit is as follows.
From the series resonance frequency fs, | Zo | = 50 kΩ, such that the absolute value | Zo | of the output impedance indicates inductive and the absolute value | Zo | of the output impedance has a current limiting element.
It can be seen that the frequency range is up to the frequency f50k. Investigation was also conducted on other well-known conventional hot cathode tubes, and it was found that the absolute value | Zo | of the output impedance was required to be 50 kΩ or less. fs to frequency f
It has been found that the frequency width up to 50 k needs to be 1 kHz or more.

In the conventional example shown in FIG. 16, | Zo |
Although the frequency at which = 50 kΩ is slightly higher than the series resonance frequency fs, it was also found that stable lighting was impossible in this frequency region because the phase was not inductive (the phase did not become 90 °).

(Embodiment 2) FIG. 7 is a block diagram showing a second embodiment of the present invention, FIG. 6 is a schematic perspective view of a piezoelectric transformer 2c used in the present embodiment, and FIG. FIG. 8 shows a frequency characteristic diagram of the output impedance and the phase in one wavelength mode (λ mode).

As shown in FIG. 6A, the piezoelectric transformer 2c
Has a laminated structure (for example, 7 mm long × 25 mm wide × 5 mm thick) made of a material manufactured by Hitachi Metals, Ltd., and has a structure in which piezoelectric bodies and electrodes alternately form layers. The primary electrode is formed on the front and back surfaces near the center of the piezoelectric body, and is a thin line shown in a cross-sectional view on an XY plane parallel to the short direction of the piezoelectric transformer 2c as shown in FIG. a and b
Indicates a primary electrode. The high voltage side of the secondary electrode is a point connecting both end surfaces of the piezoelectric body, and the low voltage side of the secondary electrode is the same as the primary electrode b. Further, as shown in FIG.
s = 83 kHz and frequency f50k = 86 kHz.

The block configuration shown in FIG.
A series circuit of a primary winding n1 and a switching element S3 of a transformer T3 connected to both ends of a DC power source E; a resonance capacitor C4 connected to both ends of a secondary winding n2 of the transformer T3; 2c, a hot-cathode tube 6, a preheating capacitor C5 connected between the non-power-supply-side terminals of the hot-cathode tube 6, and a control circuit 7 for turning on and off the switching element S3. It is. Here, a resonance capacitor C4 is connected between the primary electrodes of the piezoelectric transformer 2c, and one end of a hot cathode tube 6 is connected in series to the secondary electrode of the piezoelectric transformer 2c. Hot cathode tube 6
Is connected in series to the negative terminal of the DC power supply E.

In the above configuration, the hot cathode tube 6 can be stably lit between the series resonance frequency fs and the frequency f50k. When the inverter circuit was driven at 85 kHz, it was confirmed that the hot cathode tube 6 was stably lit.

(Embodiment 3) FIG. 9 shows a block diagram of a third embodiment of the present invention.

This configuration comprises a plurality of piezoelectric transformers 2 b 1, 2 b
b2, the output end of the piezoelectric transformer 2b1 is connected to one end of the high-pressure side filament of the hot cathode tube 6, and the output end of the piezoelectric transformer 2b2 is connected to the other end of the high-pressure side filament of the hot cathode tube 6. And the primary electrode of the piezoelectric transformer 2b1 and the piezoelectric transformer 2b at the output end of the inverter circuit.
2 primary electrodes are connected in parallel. In addition,
The inverter circuit includes a series circuit including an inductor L2 and a field effect transistor (hereinafter, referred to as a switching element) S4, and a series circuit including an inductor L3 and a field effect transistor (hereinafter, referred to as a switching element) S5. An output terminal is provided between a contact point between the inductor L2 and the switching element S4 and a contact point between the inductor L3 and the switching element S5. The low-voltage filament of the hot cathode tube 6 has a resistor R4 and a diode D
And a lamp current detection circuit for detecting a lamp current. Then, the switching element S4,
S5 is driven.

Also in this configuration, the hot cathode tube 6 can be stably lit. (Embodiment 4) FIG. 10 shows a block diagram of a fourth embodiment according to the present invention.

This configuration shows a means for preheating the filament of the hot cathode tube 6 using the piezoelectric transformer 2.
One of the power supply terminals of the hot cathode tube 6 is connected to the secondary output terminal of the piezoelectric transformer 2, and the other power supply terminal is connected to the negative terminal of the DC power source E. Is connected to a capacitor C6 for preheating.
After the preheating current is supplied through the inverter, the oscillation frequency of the inverter circuit is changed to stably light the hot cathode tube 6.

(Embodiment 5) FIG. 11 shows a block diagram of a fifth embodiment according to the present invention.

This configuration shows another embodiment of the means for preheating the filament of the hot cathode tube 6 using the piezoelectric transformer 2, and includes a secondary output terminal of the piezoelectric transformer 2 and a negative terminal of the DC power source E. A transformer T3 is connected between the two, and a preheating current is supplied to both filaments of the hot cathode tube 6 from an intermediate tap of the transformer T3 during preheating, and then the oscillation frequency of the inverter circuit is changed to stably light the hot cathode tube 6. is there.

(Embodiment 6) FIG. 12 shows a block diagram of a sixth embodiment according to the present invention.

This configuration shows another form of the means for preheating the filament of the hot cathode tube 6 using the piezoelectric transformer 2. A primary winding N 1 of a transformer T 4 is provided at both ends of the hot cathode tube 6. One end of the secondary winding N2 of the transformer T4 is connected in series to one filament of the hot cathode tube 6, and the DC power supply E1 is connected to both ends of the hot cathode tube 6 via the secondary winding N2 of the transformer T4. Then, at the time of preheating, DC power supply E1 → transformer T
4 secondary winding N2 → one filament of hot cathode tube 6 →
After supplying a preheating current to both filaments of the hot cathode tube 6 through the primary winding N1 of the transformer T4 → the other filament of the hot cathode tube 6 → DC power supply E1, the inverter circuit is driven to drive the piezoelectric transformer 2. Then, the hot cathode tube 6 is stably lit.

Here, at the time of preheating, no DC current flows into the piezoelectric transformer 2 and the same voltage is applied to the primary winding N1 and the secondary winding N2 of the transformer T4.
The voltage indicated by V in the figure is substantially zero.

(Embodiment 7) FIG. 13 is a block diagram of a seventh embodiment according to the present invention.

In this configuration, the primary electrodes of the plurality of piezoelectric transformers 2 are connected in parallel to the inverter circuit INV, the secondary output terminals of each piezoelectric transformer 2 are connected to the filament end of the hot cathode tube 6, and each piezoelectric transformer 2 Output voltage difference, the hot cathode tube 6
For preheating the filament. With this configuration, it is possible to use the output voltage difference due to the variation of the piezoelectric transformer as a preheating effect.

The fourth to seventh embodiments or other preheating means may be used in the first to third embodiments.

[0039]

According to the first to seventh aspects of the present invention, in a discharge lamp lighting device provided with a piezoelectric transformer, deterioration of the piezoelectric transformer can be prevented and the hot cathode tube can be stably lit. An electric lamp lighting device can be provided at low cost.

[Brief description of the drawings]

FIG. 1 shows a block configuration diagram of a first embodiment according to the present invention.

FIG. 2 is a schematic perspective view of the piezoelectric transformer according to the embodiment.

FIG. 3 shows an equivalent circuit diagram of the piezoelectric transformer according to the embodiment.

FIG. 4 shows a frequency characteristic diagram of output impedance and phase in the one-wavelength mode of the piezoelectric transformer according to the embodiment.

FIG. 5 is a characteristic diagram of a lamp current with respect to an output impedance according to the embodiment.

FIG. 6 is a schematic perspective view of a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 7 shows a block diagram according to the embodiment.

FIG. 8 shows a frequency characteristic diagram of an output impedance and a phase in a one-wavelength mode of the piezoelectric transformer according to the embodiment.

FIG. 9 shows a block diagram of a third embodiment according to the present invention.

FIG. 10 shows a block diagram of a fourth embodiment according to the present invention.

FIG. 11 shows a block diagram of a fifth embodiment according to the present invention.

FIG. 12 shows a block diagram of a sixth embodiment according to the present invention.

FIG. 13 shows a block diagram of a seventh embodiment according to the present invention.

FIG. 14 shows a block diagram of a conventional example according to the present invention.

FIG. 15 is a schematic perspective view of a piezoelectric transformer according to the conventional example.

FIG. 16 shows a frequency characteristic diagram of output impedance and phase in a one-wavelength mode of the piezoelectric transformer according to the conventional example.

[Explanation of symbols]

 2 Piezoelectric transformer 6 Hot cathode tube

Claims (7)

[Claims] 1. A discharge lamp lighting device comprising: a discharge lamp; an inverter circuit for converting a DC voltage to an AC high-frequency voltage; and a piezoelectric transformer for transforming a high-frequency voltage output of the inverter circuit and supplying the output to the discharge lamp. When the discharge lamp is turned on, the piezoelectric transformer is driven at a frequency equal to or higher than the series resonance frequency at which the phase becomes substantially zero and at a frequency f50k or lower at which the absolute value | Zo | of the output impedance becomes approximately 50 kΩ. Discharge lamp lighting device. 2. The piezoelectric transformer according to claim 1, wherein said piezoelectric transformer has a frequency f50.
The phase at k is approximately 90 degrees.
The discharge lamp lighting device as described in the above. 3. The discharge lamp lighting device according to claim 1, wherein the piezoelectric transformer has a difference between the series resonance frequency and the frequency f50k of 1 kHz or more. 4. The piezoelectric transformer has a single-plate shape, and has a primary electrode formed on one of the front and back surfaces, which is substantially halved in the short direction, and a secondary electrode formed on an end surface on the other side. And an electrode.
The discharge lamp lighting device according to any one of the above. 5. The discharge lamp lighting device according to claim 1, wherein the piezoelectric transformer has a structure in which piezoelectric bodies and electrodes are alternately formed in layers. . 6. The discharge lamp lighting device according to claim 1, wherein the discharge lamp is a hot cathode type. 7. The discharge lamp lighting device according to claim 1, further comprising means for preheating the discharge lamp.