JP2001093691A - Discharge lamp lighting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the drive voltage waveform having many distortions and a discontinuous part and the inverting efficiency of a piezoelectric transformer and to prevent the piezoelectric transformer from being abnormally heated in an inverter for lighting a neon tube with a pulsating DC waveform by driving the piezoelectric transformer by a push-pull resonance circuit. SOLUTION: This lighting apparatus, in which a piezoelectric transformer is driven by a push-pull inverter circuit with a resonance circuit and a neon tube is lighted with a pulsating DC waveform by the output of the piezoelectric transformer, has a means for making the input voltage to the piezoelectric transformer nearly continuous waveform. Specifically, the waveform of the input voltage to the piezo-electric transformer is made nearly sinewave with few higher harmonics by unbalancing the duty ratio of the on/off signal of a pair of switching elements constituting the push-pull inverter circuit or unbalancing the circuit constant of resonance elements constituting the push-pull inverter circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device for lighting a neon tube with a pulsating DC waveform using a piezoelectric transformer.

[0002]

2. Description of the Related Art Conventionally, as a method of lighting a neon tube, a method of lighting a neon tube with a pulsating DC waveform has been proposed in order to prevent moving fringes and increase luminous efficiency. For example, as shown in FIG. 9, a piezoelectric transformer 1 having features such as high efficiency and thinness is driven by using a piezoelectric transformer driving circuit 2 including a high frequency inverter, and the output of the piezoelectric transformer 1 is diode D and neon tube N. A method of lighting the neon tube N with a pulsating DC waveform by applying the voltage to the parallel circuit of the above. The pulsating DC waveform is a half-wave AC waveform, and is the sum of an AC component, a DC component, and a harmonic component.

As a drive circuit 2 for the piezoelectric transformer 1, there is a circuit for driving the piezoelectric transformer 1 by a push-pull resonance circuit proposed in Japanese Patent Application Laid-Open No. 8-275553. This is because the boosting action of the resonance circuit is large, the neon tube N can be turned on even with a low-voltage power supply E, and the piezoelectric transformer 1 can be driven by a substantially sine-wave voltage by the push-pull resonance circuit, so that efficiency is high. It is known.

FIG. 10 shows a conventional example using a drive circuit based on this push-pull resonance. The piezoelectric transformer drive circuit 2 shown in FIG. 10 controls the auto transformers Ta and Tb, the switching elements Sa and Sb, the capacitor Cs for assisting the resonance capacity of the piezoelectric transformer 1, and the switching elements Sa and Sb to be turned on and off alternately. It is composed of circuit 3,
The piezoelectric transformer 1 is driven by generating a substantially sinusoidal resonance voltage by the push-pull resonance of the auto transformers Ta and Tb, the piezoelectric transformer 1 and the capacitor Cs.

FIG. 11 shows waveforms at various points in the conventional example shown in FIG. In the drawing, a and b are drive signal waveforms for alternately turning on and off the switching elements Sa and Sb, Va and Vb are signal waveforms of primary voltages of the auto transformers Ta and Tb, and Vc is a signal to the piezoelectric transformer 1. 5 is a signal waveform of the input voltage of FIG. The autotransformers Ta and Tb have the same inductance value, and the drive signals a and b for alternately turning on and off the switching elements Sa and Sb have the same duty ratio of 50%. The resonance waveforms of the primary voltages Va and Vb are the same, and the input voltage waveform Vc to the piezoelectric transformer 1 is a substantially sine wave.

[0006]

However, it has been found that there is a problem when attempting to pulsate DC light the neon tube N using this drive circuit. This is because, when observed, the input voltage waveform Vc to the piezoelectric transformer 1 does not become a substantially sinusoidal wave as shown in FIG. 11, but has a large amount of distortion and a discontinuous portion as shown in FIG. The result is a waveform Vc. As described above, when the piezoelectric transformer 1 is driven by a voltage waveform having a large amount of distortion and a discontinuous portion, a significant reduction in efficiency is observed. This is considered to cause an increase in the voltage of a higher harmonic component with respect to the fundamental wave and loss of the portion other than the fundamental wave, thereby lowering the efficiency and causing abnormal heat generation of the piezoelectric transformer 1.

In the drive circuit shown in FIG. 10, the reason why the input voltage waveform Vc to the piezoelectric transformer 1 becomes a voltage having a large amount of distortion and a discontinuous portion is that the output of the piezoelectric transformer 1 uses only a half-wave, This is because lighting is performed in a pulsating DC waveform. As shown in the circuit configuration of FIG. 10, a diode D is connected in parallel with the neon tube N to output half-wave to the output of the piezoelectric transformer 1, and the load of the piezoelectric transformer 1 is switched every half cycle. become. Since the piezoelectric transformer 1 has a very large load dependency, when the load is switched every half cycle, the equivalent impedance of the piezoelectric transformer 1 changes accordingly, and the resonance waveforms Va and Vb with the auto transformers Ta and Tb are shown in FIG. The input voltage waveform V of the piezoelectric transformer 1 which is an asymmetrical waveform as shown in FIG.
It is considered that distortion and discontinuous portions occur in c.

Further, it is considered that this phenomenon is caused by the large load dependency peculiar to the piezoelectric transformer.
Even when the impedance of the neon tube, which is a load, changes depending on the gas pressure, the tube diameter, and the tube length of the tube, the degree of the resonance waveform changes, which may cause a change in efficiency or heat generation.

In view of the above, the present invention is to improve a driving voltage waveform of a piezoelectric transformer having a large amount of distortion and a discontinuous portion in an inverter that drives a piezoelectric transformer with a push-pull resonance circuit and lights a neon tube with a pulsating DC waveform. An object of the present invention is to improve conversion efficiency and prevent abnormal heat generation of a piezoelectric transformer.

[0010]

According to the discharge lamp lighting device of the present invention, in order to solve the above-mentioned problems, as shown in FIG. 10, the piezoelectric transformer 1 is driven by a push-pull inverter circuit having a resonance circuit. The lighting device for lighting the neon tube N with a pulsating DC waveform by the output of the piezoelectric transformer 1 is characterized by comprising means for making the input voltage to the piezoelectric transformer 1 a substantially continuous waveform. Specifically, the duty ratios d1, d of the on / off signals of the pair of switching elements Sa, Sb forming the push-pull inverter circuit
2 is unbalanced as shown in FIG. 1, or
By making the circuit constants (Ca, Cb in FIG. 2) of the resonance elements constituting the push-pull inverter circuit unbalanced, the input voltage waveform to the piezoelectric transformer 1 can be made a substantially sine wave with few high-order harmonics. preferable.

Also, as shown in FIG. 3, a resonance voltage detecting means 4 for detecting a resonance voltage of the push-pull inverter circuit.
And an on / off signal of a pair of switching elements Sa and Sb forming a push-pull inverter circuit, based on a detection output of the resonance voltage detecting means 4.
It is more preferable to add a control means 3 for controlling the input voltage Vc to a direction having a substantially continuous waveform.

Further, as shown in FIG. 4, diodes D1, D2 and neon tubes N1, N2 are connected to the output of the piezoelectric transformer 1.
The two series circuits are connected in anti-parallel and the output of the piezoelectric transformer 1 turns on the two neon tubes alternately every half cycle with a pulsating DC waveform, so that the load of the piezoelectric transformer 1 fluctuates every half cycle. May be prevented.

[0013]

(Embodiment 1) FIG. 1 is an operation waveform diagram of Embodiment 1 of the present invention. The circuit configuration of the present embodiment is the same as the conventional example of FIG.
Only the duty ratios d1 and d2 of the driving signals a and b of Sb are different from the conventional example. Piezoelectric transformer drive circuit 2 of FIG.
Are the auto transformers Ta and Tb and the switching element S
a and Sb, a capacitor Cs for assisting the resonance capacity of the piezoelectric transformer 1, and a control circuit 3 for alternately turning on and off the switching elements Sa and Sb. The auto transformers Ta and Tb, the piezoelectric transformer 1, and the capacitor C
The piezoelectric transformer 1 is driven by generating a substantially sinusoidal resonance voltage Vc by s push-pull resonance. The positive pole of the input DC power supply E is connected to one ends of the auto transformers Ta and Tb, and the other ends of the auto transformers Ta and Tb are connected to a pair of input terminals of the piezoelectric transformer 1, respectively. The intermediate terminals of the auto transformers Ta and Tb are connected to the negative electrode of the input DC power supply E via the switching elements Sa and Sb, respectively. A resonance auxiliary capacitor Cs is connected in parallel between a pair of input terminals of the piezoelectric transformer 1. A neon tube N and a diode D are connected between the output terminal of the piezoelectric transformer 1 and the negative terminal of the input DC power supply E as a circuit ground.
Are connected. In the circuit configuration of FIG. 10, the duty ratio of the drive signals a and b for alternately turning on and off the switching elements Sa and Sb is not 50%, but the voltage V applied to the piezoelectric transformer 1 as shown in FIG.
The control circuit 3 controls the duty ratios d1 and d2 so that c has a substantially continuous waveform.

In the circuit configuration shown in FIG. 10, the piezoelectric transformer 1 is a Rosen type element that resonates at 160 kHz in a λ / 2 mode, has an input side capacitance of 3 nF, and an output side capacitance of 100 pF. The neon tube N has a tube length of 400 mm and a tube length of 400 mm. Diameter Φ4mm,
A transformer having a gas pressure of 100 Torr is used. The auto transformers Ta and Tb each have a turns ratio of 1: 2 and a primary inductance value of 50 μH.
The case where s is 3 nF and a half-wave current of about 12 mA flows through the neon tube N will be described. When the switching elements Sa and Sb are alternately turned on and off at a duty ratio of 50% as in the related art, the waveforms of the respective parts are as shown in FIG.
The input power of the circuit was 15 W, and the surface temperature rise of the piezoelectric transformer 1 was about 50 deg. On the other hand, as in the present embodiment, the duty ratios d1, d of the drive signals a, b for alternately turning on and off the switching elements Sa, Sb.
When 2 is unbalanced to 40% and 60% respectively,
As shown in FIG. 1, the input voltage waveform Vc of the piezoelectric transformer 1 is a continuous voltage waveform, and the input power of the circuit is about 1
At 2.5 W, the surface temperature rise of the piezoelectric transformer 1 is about 25 d
eg.

As described above, the duty ratio d of the ON / OFF signal of the pair of switching elements Sa and Sb constituting the push-pull resonance circuit for driving the piezoelectric transformer 1
By making 1 and d2 unbalanced, the occurrence of distortion or discontinuity in the input voltage Vc of the piezoelectric transformer 1 is suppressed even in pulsating DC lighting, the voltage of high-order harmonic components is suppressed, and the efficiency is reduced. In addition, abnormal heat generation of the piezoelectric transformer 1 can be prevented.

(Embodiment 2) FIG. 2 shows Embodiment 2 of the present invention.
FIG. 3 is a circuit configuration diagram of FIG. In the second embodiment, in the circuit configuration of FIG. 2, instead of the resonance auxiliary capacitor Cs connected in parallel to the piezoelectric transformer 1, the resonance auxiliary capacitors Ca and Ca are respectively connected between the input terminals of the piezoelectric transformer 1 and the ground.
Cb is connected. In the circuit configuration of FIG.
The resonance auxiliary capacitors Ca and Cb are each 2.5 nF,
3.5 nF, and the other configuration is the same as that of the first embodiment.
The duty ratios of the drive signals a and b for turning on and off the switching elements Sa and Sb alternately are each 50%.

At this time, the resonance auxiliary capacitors Ca, Cb
Are designed to be unbalanced, the resonance voltage waveforms Va and Vb as shown in FIG. 11 can be realized, and the input voltage Vc of the piezoelectric transformer 1 becomes a substantially sine wave voltage waveform, and the input power of the circuit Was about 12.0 W, and the surface temperature rise of the piezoelectric transformer 1 was about 20 deg.

As described above, by making the resonance elements constituting the push-pull inverter circuit of the piezoelectric transformer drive circuit 2 unbalanced, the input voltage waveform Vc of the piezoelectric transformer 1 can be made substantially sinusoidal even with pulsating DC lighting. Can,
There is a great effect on circuit efficiency and heat generation of the element.

In the configuration shown in FIG. 10, the switching elements Sa and Sb are alternately turned on and off even when the values of the primary inductances of the auto transformers Ta and Tb are imbalanced to 40 μH and 60 μH, respectively. The input voltage Vc to the piezoelectric transformer 1 can be made substantially sinusoidal with the duty ratios of the drive signals a and b kept at 50%, respectively, which has a great effect on the circuit efficiency and the heat generation of the elements.

(Embodiment 3) FIG. 3 shows Embodiment 3 of the present invention.
FIG. 3 is a circuit configuration diagram of FIG. The third embodiment is different from the circuit shown in FIG. 10 in that the resonance voltages Va and Vb are detected and the duty ratios of the drive signals a and b of the control circuit 3 are controlled so that the voltage waveforms become substantially continuous. 4 is added. As described above, even if the resonance voltages Va and Vb are asymmetric due to the pulsating DC lighting, the resonance voltages Va and Vb are not asymmetric.
Since the waveform of Vb is detected and the duty ratio of the switching elements Sa and Sb is controlled so as not to generate distortion or discontinuity, a substantially continuous waveform as shown in the input voltage Vc of FIG. it can. Further, even when the impedance of the neon tube N or the input / output impedance of the piezoelectric transformer 1 changes and the degree of the resonance waveform changes, a substantially continuous waveform can be maintained by control based on the detection output of the resonance voltage detection circuit 4.

As described above, the configuration in which the duty ratio of the switching elements Sa and Sb is controlled by the control based on the detection output of the resonance voltage detection circuit 4 enables the input voltage Vc of the piezoelectric transformer 1 to be distorted or discontinuous even when the pulsating DC is turned on. Is suppressed, the voltage of higher harmonic components is suppressed, and a decrease in efficiency and abnormal heat generation of the piezoelectric transformer 1 can be prevented.

(Embodiment 4) FIG. 4 shows Embodiment 4 of the present invention.
FIG. 3 is a circuit configuration diagram of FIG. The configuration of the fourth embodiment shown in FIG.
In the configuration of the third embodiment, two neon lamps are alternately half-wave lit. A neon tube N1 in which a diode D1 is connected in series and a neon tube N2 in which an opposite diode D2 is connected in series are connected to the output of the piezoelectric transformer 1 in parallel. Currents alternately flow through the neon tube N1 and the neon tube N2 by the diodes D1 and D2, and each of them enters a half-wave lighting state.

In this configuration, since the voltages are separately supplied to the neon tubes N1 and N2, one of them is turned on first and the other is not turned on due to insufficient starting voltage, or one of them is connected like two lamps connected in series. When they disappear, the other does not disappear. In addition, since the output of the piezoelectric transformer 1 has a constant current characteristic, an almost constant current can flow even with two lamps having different impedances.

Further, since the piezoelectric transformer drive circuit 2 is configured as in the third embodiment, even if the neon tube N1 and the neon tube N2 have different impedances, switching is performed by control based on the detection output of the resonance voltage detection circuit 4. The duty ratios of the elements Sa and Sb are controlled to suppress the occurrence of distortion and discontinuity in the input voltage Vc of the piezoelectric transformer 1,
It is possible to suppress the voltage of the high-order harmonic components, thereby preventing a decrease in efficiency and abnormal heat generation of the piezoelectric transformer 1.

(Embodiment 5) FIG. 5 shows Embodiment 5 of the present invention.
FIG. 3 is a circuit configuration diagram of FIG. In the present embodiment, in addition to the circuit configuration shown in the third embodiment, a current detection circuit 5 for detecting a current flowing through the neon tube N is provided, and the control circuit 3 controls the neon tube N based on the detection output. Is added to the function of controlling the current flowing through the device to a predetermined current. FIG.
The current detection circuit 5 detects the current flowing through the neon tube N and provides a feedback signal to the control circuit 3. The control circuit 3 of FIG. It has a function of controlling the frequency of the current flowing through the neon tube N by the feedback signal from the circuit 5 so as to be a predetermined current.

According to the present embodiment, even if the power supply voltage fluctuates, the current flowing through the neon tube N can be maintained at a predetermined current, and at this time, the drive frequency of the switching elements Sa and Sb is controlled by frequency control. And the resonance voltage Va,
Even if Vb changes, the duty ratio of the switching elements Sa and Sb is controlled based on the detection output of the resonance voltage detection circuit 4, so that the occurrence of distortion or discontinuity in the input voltage Vc of the piezoelectric transformer 1 is suppressed. In addition, it is possible to suppress the voltage of the higher-order harmonic components, thereby preventing a reduction in efficiency and abnormal heat generation of the piezoelectric transformer 1.

(Embodiment 6) FIG. 6 shows Embodiment 6 of the present invention.
FIG. 3 is a circuit configuration diagram of FIG. In this embodiment, a bypass circuit 6 is added in parallel with the current detection circuit 5 in the circuit configuration of the fifth embodiment. When the neon tube N is turned on with a pulsating DC voltage such as a half-wave alternating current, an overcurrent is applied immediately after the neon tube N is turned on, as shown in FIG. Flows. This is presumably because the electric charge in which the high voltage was accumulated in the stray capacitance at the time of starting flows at once at the same time as the lighting of the neon tube N. Embodiment 5
In the case where the lamp current is controlled by detecting the current ILa flowing through the neon tube N as shown in FIG. 7, if the overcurrent as shown in FIG. There is. Therefore, in the present embodiment, as shown in FIG. 6, a bypass circuit 6 is added in parallel with the current detection circuit 5 so that only the overcurrent flowing immediately after the neon tube N is turned on flows into the bypass circuit 6. Thus, it is possible to prevent the current detection control from becoming unstable and prevent the lighting of the neon tube N from being unable to be maintained.

FIGS. 8A, 8B and 8C show specific examples of the bypass circuit 6. FIG. In FIG. 8A, the capacitor C
8B, a series circuit of a capacitor Cp and a diode Dp is used in FIG. 8B, and a Zener diode ZD is used in FIG. 8C. Terminals A and B in the figure are terminals A and B of the circuit of FIG.
Connected to.

[0029]

According to the present invention, a piezoelectric transformer is driven by a push-pull inverter circuit having a resonance circuit,
A lighting device for lighting a neon tube with a pulsating DC waveform by the output of a piezoelectric transformer is provided with means for making the input voltage to the piezoelectric transformer a substantially continuous waveform.
Even when the lamp is turned on, the occurrence of distortion or discontinuous portions in the input voltage of the piezoelectric transformer is suppressed, higher-order harmonic components that cause conversion loss are suppressed, and a reduction in efficiency and abnormal heat generation of the piezoelectric transformer can be prevented.

The duty ratio of the on / off signal of the switching element constituting the push-pull inverter circuit or the unbalanced resonance element makes it possible to obtain a piezoelectric transformer having a simple configuration even when pulsating DC lighting is performed. Can be made into a substantially sine wave having less harmonic components, and can be driven efficiently.

Further, by detecting the resonance voltage and performing feedback control, even if the impedance of the neon tube or the input / output impedance of the piezoelectric transformer changes and the degree of the resonance waveform changes, the input voltage to the piezoelectric transformer is substantially reduced. A continuous waveform can be maintained, and a decrease in efficiency and abnormal heat generation of the piezoelectric transformer can be prevented.

Further, two series circuits of a diode and a neon tube are connected in anti-parallel to the output of the piezoelectric transformer, and the two neon tube lamps are alternately turned on every half cycle with a pulsating DC waveform by the output of the piezoelectric transformer. Accordingly, it is possible to prevent the load of the piezoelectric transformer from changing every half cycle. This allows
The two neon lamps can be stably turned on, and the output of the piezoelectric transformer has a constant current characteristic, so that the impedance is different.
Almost constant current can be passed even with lamps,
Abnormal heat generation of the piezoelectric transformer can be prevented.

Further, current detecting means for detecting a lamp current flowing through the neon tube is provided, and the lamp current of the neon tube is controlled based on the lamp current detected by the current detecting means, so that the power supply voltage fluctuates. Even so, the current of the neon tube can be maintained at a predetermined current, and a decrease in efficiency and abnormal heating of the piezoelectric transformer can be prevented. In this case, by providing bypass means for bypassing the inrush current at the time of starting in parallel with the current detection means for detecting the lamp current of the neon tube, it is possible to prevent the control based on the current detection output from becoming unstable, It can be prevented that the lighting of the tube cannot be maintained.

[Brief description of the drawings]

FIG. 1 is an operation waveform diagram according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a circuit configuration according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram illustrating a circuit configuration according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram illustrating a circuit configuration according to a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a circuit configuration according to a fifth embodiment of the present invention.

FIG. 6 is a circuit diagram illustrating a circuit configuration according to a sixth embodiment of the present invention.

FIG. 7 is a waveform diagram showing a current flowing when starting the neon tube of the circuit of FIG. 6;

FIG. 8 is a circuit diagram showing a circuit example of a bypass circuit used in a sixth embodiment of the present invention.

FIG. 9 is a circuit diagram of Conventional Example 1.

FIG. 10 is a circuit diagram of a second conventional example.

FIG. 11 is a waveform chart for explaining the operation of Conventional Example 2.

FIG. 12 is a waveform chart for explaining a problem of the second conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 piezoelectric transformer 2 piezoelectric transformer drive circuit 3 control circuit 4 resonance voltage detection circuit 5 current detection circuit 6 bypass circuit N neon tube D diode E DC power supply Sa switching element Sb switching element d1 on-duty of switching element Sa d2 switching element Sb On-duty Va Input voltage of auto transformer Ta Vb Input voltage of auto transformer Tc Vc Input voltage of piezoelectric transformer 1

Claims (12)

[Claims] 1. A lighting device in which a piezoelectric transformer is driven by a push-pull inverter circuit having a resonance circuit, and an output of the piezoelectric transformer lights a neon tube in a pulsating DC waveform, so that an input voltage to the piezoelectric transformer has a substantially continuous waveform. A discharge lamp lighting device comprising means. 2. The discharge lamp lighting device according to claim 1, wherein the input voltage waveform to the piezoelectric transformer is substantially a sine wave. 3. The discharge lamp lighting device according to claim 1, wherein the input voltage waveform to the piezoelectric transformer is set in a direction in which high-order harmonics are reduced. 4. The method according to claim 1, wherein a pair of switching elements constituting the push-pull inverter circuit are turned on and off.
A discharge lamp lighting device, wherein a duty ratio of an off signal is unbalanced. 5. The discharge lamp lighting device according to claim 1, wherein circuit constants of resonance elements constituting the push-pull inverter circuit are unbalanced. 6. A resonance voltage detecting means according to claim 1, wherein said resonance voltage detecting means detects a resonance voltage of said push-pull inverter circuit.
Control means for controlling on / off signals of a pair of switching elements constituting the push-pull inverter circuit in a direction in which the input voltage to the piezoelectric transformer has a substantially continuous waveform based on the detection output of the resonance voltage detecting means is added. A lighting device for a discharge lamp, comprising: 7. The discharge lamp lighting device according to claim 1, wherein the two neon lamps are alternately lighted in a pulsating DC waveform every half cycle by the output of the piezoelectric transformer. 8. The circuit according to claim 7, wherein a series circuit of the first diode and the first neon tube, and a series circuit of the second diode and the second neon tube are oriented in the directions of the first and second diodes. A discharge lamp lighting device, which is connected in parallel to the output of a piezoelectric transformer so that the directions of the discharge lamps are opposite. 9. The apparatus according to claim 6, further comprising current detection means for detecting a lamp current flowing through the neon tube, wherein the control means detects a lamp current of the neon tube based on the lamp current detected by the current detection means. A discharge lamp lighting device, which also serves as a control unit. 10. The control device according to claim 9, wherein the operation of controlling the input voltage to the piezoelectric transformer to a substantially continuous waveform based on the detection output of the resonance voltage detecting device varies the duty of the switching element. A discharge lamp lighting device, wherein the operation of controlling the lamp current of the neon tube based on the lamp current detected by the current detection means is an operation of changing the frequency of the switching element. 11. The method according to claim 6, further comprising a current detection unit for detecting a lamp current flowing through the neon tube, wherein the control unit detects the lamp current when the lamp current detected by the current detection unit becomes excessive. A discharge lamp lighting device, which also serves as overcurrent protection means for controlling in a direction to suppress. 12. The discharge lamp lighting device according to claim 9, further comprising bypass means for bypassing an inrush current at the time of starting in parallel with current detection means for detecting a lamp current of the neon tube.