KR100402432B1 - Inverter circuit for discharging tube - Google Patents

Abstract

[purpose]

Even if the driving frequency is increased for the miniaturization of the step-up transformer or the like, the lighting luminance of the discharge tube is not lowered, and even if the parasitic capacitance around the discharge tube is increased, the voltage for applying the voltage to the discharge tube is lowered to lower the lighting luminance of the discharge tube The inverter circuit for the discharge tube is provided.

[Configuration]

The discharge tube inverter circuit includes a high-frequency oscillation circuit OS and a step-up transformer T for boosting the output thereof, and a discharge tube DT is connected to the secondary side thereof. An impedance matching circuit 10 for impedance matching between the circuit up to the secondary side and the discharge tube is connected to the secondary side of the step-up transformer.

A step-up transformer is composed of a leakage flux-type winding transformer or a piezoelectric transformer having a secondary winding having at least one tight coupling portion and a small coupling portion tightly coupled with each other and a small coupling with the primary winding.

Description

Inverter circuit for discharging tube

[Industrial Applications]

The present invention relates to an inverter circuit for a discharge tube for lighting and driving a discharge tube such as a cold cathode fluorescent tube, a hot cathode fluorescent tube, a mercury lamp, a sodium lamp, a metal halide lamp or the like.

[0003]

In recent years, in order to miniaturize the lighting circuit and to supply a portable device, a high-voltage power source is obtained from a low-voltage direct-current power source in order to lighten the discharge tube, in addition to a commercial power source, a high-voltage power source and a ballast for current limitation. The inverter circuit was used.

Conventionally, as the inverter circuit of this kind, a structure as shown in Fig. 9 is generally used. The illustrated inverter circuit includes a pair of transistors Q ₁ and Q ₂ and a boost transformer T having a primary winding L ₁ , a secondary winding L ₂ and an auxiliary winding L ₃ , ₁ and Q ₂ are connected to both ends of the primary winding L ₁ of the step-up transformer T and the emitters are connected to each other and connected to the ground. The intermediate point of the primary winding L ₁ is connected to the base of the transistors Q ₁ and Q ₂ through the resistors R ₁ and R ₂ and both ends of the auxiliary winding L ₃ of the voltage- Respectively. The primary winding L1 of the step-up transformer T, the capacitor C ₁ connected in parallel with the primary winding L1, the transistors Q ₁ and Q ₂ and the auxiliary winding L ₃ are connected in series to the high- And constitutes an oscillation circuit (OS).

One end of the secondary winding L ₂ of the step-up transformer T is connected to one end of the discharge tube DT via the ballast capacitor C ₂ and the wiring L and the other end thereof is connected to the ground as the other end of the discharge tube DT Respectively. C ₃ is the parasitic capacitance of the secondary winding L ₂ , and C ₄ is the parasitic capacitance generated around the discharge tube DT.

In the case of the above-described inverter circuit, it is the step-up transformer which requires the maximum space in this circuit, and the downsizing of the step-up transformer is difficult to reduce the overall shape of the inverter circuit. In order to achieve miniaturization of the step-up transformer, it is necessary to increase the driving frequency thereof, but in this way, the entire inverter circuit can be downsized.

[Problems to be solved by the invention]

It is difficult to say that the impedance of the load seen from the high impedance side of the power source and the impedance of the power source side from the load side are matched with each other. Do. As a result, the driving frequency becomes high, and reflection is caused to the load side, so that a part of the supplied power returns to the power source side.

Incidentally, due to mismatching of the impedance, the phase of the voltage and the current is deviated as shown in FIG. 10 and effectively used. There arises a problem that the power returning back and forth increases, and accordingly, the increase of the reactive current increases the copper damage or the dielectric loss, and the power conversion efficiency decreases. Also, even if the voltage RMS value and the current RMS value are multiplied, the power supplied to the discharge tube can not be obtained.

When the driving frequency is increased, the value of the ballast capacitor C ₂ is reduced by design. However, if the driving frequency is increased, the ratio of the parasitic capacitance C ₃ to the ballast capacitor C ₂ becomes higher, So that the lighting brightness of the discharge tube DT is greatly lowered.

When a reflective member made of a conductive sheet formed by sputtering silver on a PET film is used, the parasitic capacitance around the discharge tube is further increased, and the parasitic capacitance around the discharge tube is increased to the discharge tube So that the lighting brightness of the discharge tube DT is greatly lowered.

This phenomenon also occurs in the case of using a piezoelectric transformer as the step-up transformer. A partial pressure effect similar to that of a conventional winding transformer is produced between the characteristic capacitance corresponding to the ballast capacitor C ₂ and the parasitic capacitance C ₃ contained in the equivalent circuit of the piezoelectric transformer, The lighting brightness decreases. As a piezoelectric transformer, a decrease in lighting luminance due to the conductive reflective sheet is unavoidable. Therefore, in order to reduce the partial pressure effect, a problem arises that the shape of the piezoelectric transformer must be increased and the characteristic capacitance C ₂ must be increased there was.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an inverter circuit for a discharge tube that does not lower the lighting luminance of a discharge tube even if the driving frequency is increased for miniaturization of a step-up transformer or the like.

It is another object of the present invention to provide an inverter circuit for a discharge tube in which the voltage applied to the discharge tube is lowered even when the parasitic capacitance of the periphery of the discharge tube is increased, and the luminance of the discharge tube is not lowered.

[MEANS FOR SOLVING THE PROBLEMS]

In order to achieve the above object, an inverter circuit for a discharge tube according to the present invention comprises a high-frequency oscillation circuit and a step-up transformer for stepping up an output of the high-frequency oscillation circuit. The discharge tube is connected to the secondary side of the step- In the inverter inverter circuit, an impedance matching circuit for impedance matching between a circuit up to the secondary side and a discharge tube is connected to the secondary side of the step-up transformer.

Wherein the impedance matching circuit comprises a high-frequency choke coil inserted in series between one end of the secondary side of the step-up transformer and one end of the discharge tube, and a parasitic capacitance of the secondary side of the step-up transformer and a parasitic capacitance generated around the discharge tube. .

When the parasitic capacitance does not reach the matching condition, the parasitic capacitance is added to the parasitic capacitance so that the matching condition is established.

Wherein the step-up transformer comprises a primary winding and a leakage flux-type winding transformer having a secondary winding having at least one tight coupling portion and a small coupling portion tightly coupled to the primary winding and a small coupling with respect to the primary winding, A secondary side parasitic capacitance of the winding transformer and a matching circuit formed by an inductive component formed in the sintered portion of the secondary winding so as to act as an inductive ballast at the time of lighting the discharge tube and an auxiliary capacitance adhered to the parasitic capacitance of the discharge tube, .

Wherein the step-up transformer comprises a piezoelectric transformer, and the matching circuit is formed by a parasitic capacitance of a high-frequency choke coil and a discharge tube to which the impedance matching circuit is supplementally provided.

[Action]

In the above configuration, since the discharge tube is connected to the secondary side of the step-up transformer that boosts the output of the high-frequency oscillation circuit through the impedance matching circuit to perform the impedance matching between the circuit up to the secondary side of the step-up transformer and the discharge tube, The impedance of the load is matched with the impedance of the power source side on the load side and the boosted high frequency power is reflected on the load side so that a part of the supplied power does not return to the power source side. In particular, the impedance matching circuit includes a high-frequency choke coil inserted in series between one end of the secondary side of the step-up transformer and one end of the discharge tube, and a parasitic capacitance of the secondary side of the step-up transformer and a parasitic capacitance generated around the discharge tube. The current limit at the time of lighting the discharge tube is suitably controlled by the inductive ballast made of the high frequency choke coil and the parasitic capacitance at the discharge tube side is reduced as in the case of winding the conductive reflection sheet around the discharge tube by use of this high frequency choke coil The voltage applied to the discharge tube does not decrease.

It is preferable that the step-up transformer comprises a winding flux transformer of a leakage magnetic flux type, and the secondary winding has at least one tightly coupled portion and a smallly-engaged portion tightly coupled to the primary winding and the small- Since the matching circuit formed by the induction component formed in the sintered joint portion of the secondary winding and the parasitic capacitance of the discharge tube or the like and the auxiliary capacitance provided in an auxiliary manner to operate as the inductive ballast when the discharge tube is lit is used as the impedance matching circuit, In order to construct a matching circuit, it is necessary to connect inductive ballasts in particular, and further, a high high-frequency voltage that has been stepped up is applied to the discharge tube until the discharge tube is turned on, and after the discharge tube is turned on, So that a limited power can be supplied.

Furthermore, when a piezoelectric transformer is used as a step-up transformer, a matching circuit formed by a ballast capacitance characteristically included in a piezoelectric transformer, a supplementary capacitance supplementarily provided, and a parasitic capacitance of a high-frequency choke coil and a discharge tube is used as an impedance matching circuit Therefore, the impedance of the discharge tube is increased by the high step-up ratio immediately before the lighting, and the discharge tube is lighted stably at the time of the normal discharge. Thus, the impedance of the load seen from the power source side and the The impedance of the power source is matched and the raised high frequency power is reflected to the load side to prevent a part of the supplied power from returning to the power source side. For example, the power factor can be improved and the conversion efficiency can be improved.

Naturally, even when a conductive reflective sheet is used as a reflector of a discharge tube, a decrease in luminance can be prevented.

[Example]

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a principle structure of an embodiment of an inverter circuit according to the present invention, and the same reference numerals are given to the same parts as those described above with reference to FIG. In the figure, the secondary winding (L ₂₎ between the other hand the terminals of the one and the discharge tube (DT) is the impedance of the discharge tube on the secondary winding (L2) of a boost transformer (T) of the (DT) of the step-up transformer (T) And an impedance matching circuit 10 matching the impedance seen from the side of the impedance matching circuit 10 is inserted. The impedance matching circuit 10 is constituted of a parasitic capacitance of the secondary winding L ₂ and a parasitic capacitance generated around the discharge tube DT and the output of the secondary winding L ₂ is reflected by the discharge tube DT So that the output of the secondary winding L ₂ can be efficiently transmitted to the discharge tube DT.

Second and turning impedance discloses a specific circuit example of the matching circuit 10, circuit 10 is inserted in series between the one end and the one end and the discharge tubes (DT) of the secondary winding (L ₂₎ of the step-up transformer (T) a high frequency choke coil (10 _a) and the step-up transformer is a (T) the secondary side of the parasitic capacitance (C ₃₎ and discharge tube impedance composed of a π-type matching circuit consisting of a parasitic capacitance (C ₄₎ occurs in the vicinity of the (DT) matching circuit .

In addition, Cs is the is the capacity due to the parasitic capacitance (C ₄₎ is a storage capacitor is added in parallel at the time runs out, the design condition is the matching adjustment of impedance, but is performed by the capacitance generated at the periphery of the discharge tube (DT) 0 < / RTI >

In order to calculate the combined capacitance (C) of the inductance (L _a) and a parasitic capacitance (C ₃₎ and the parasitic capacitance (C ₄₎ and the storage capacitor (Cs) of the choke coil (10 _a) of the π-type matching circuit of the It may be considered to be replaced with an equivalent circuit of three degrees. In the figure, Zp is the impedance of the secondary-side load, R is _a resistance of the discharge tube (DT), which are pre-assigned. L _a is divided into two parts of L _a1 and L _a2, C _3, is determined by the L _a1, L _a2 and C as follows. L _a2 , C and R _a are eliminated, and C3, L _a1 and R s, which can be the impedance viewed from the left side, are obtained when the resistor Rs is connected instead of them. Here, _letting the reactances of C ₃ and L _a1 be Xc ₃ and X _a1 , respectively, the constants can be determined by the following equation (1) if the Q of the circuit of Zp is determined.

Reflect Rs ( L _a2 , C, and R _a from one terminal are obtained as L _a2 and C such that the impedance becomes R s. Here, assuming that the reactance of L _a2 and C X _a1, X _a2, Xc, when obtained by the above formula (1), the resistance (R _a) of Rs and a discharge tube (DT) given are each an integer by the food (2) Can be determined.

Where Q 'is the Q of the circuit of L _a2 , C, R _a .

C ₃ , L _a and C in the above equations (1) and (2) can be calculated by the following equation (3).

Where f is the drive frequency.

2, the oscillation signal of the high-frequency oscillating circuit constituted on the primary side of the step-up transformer T is stepped up to be induced in the secondary winding L ₂ , The induced high frequency high voltage is supplied to the discharge tube DT without reflection by the action of the impedance matching circuit 10.

First by using Fig. 2 that the method, embodiment examples of the high frequency choke coil (10 _a) The leakage flux type of structure such as that shown as does any whether not particularly mentioned, the step-up transformer (T) in FIG. 4 and FIG. 5 in may have the function of the choke coil (10 _a) in a portion of the secondary winding (L2) of a boost transformer (T). The leakage magnetic flux type step-up transformer T shown in FIGS. 4 and 5 is employed in order to obtain an extreme leak magnetic flux type. In the embodiment of FIG. 4, the embodiment has a cylindrical shape, A columnar shape or the like, and in the embodiment of FIG. 5, there is no shape on a flat disk.

4, an auxiliary winding (pass coil) L ₃ of a step-up transformer T is provided at one end of a bobbin 11, into which a rod-shaped core (not shown) And a primary winding (collector winding) L ₁ is wound around the secondary winding L ₂ adjacent thereto, and the secondary winding L ₂ is wound around the secondary winding L ₂ . Forward of the secondary winding (L ₂₎ has, starting from the vicinity of the primary winding (L ₁₎ ends at the end (11a) formed on the other end of the bobbin (11).

When _{one end} of the secondary winding L ₂ adjacent to the primary winding L ₁ is grounded, the voltage at the end of the secondary winding L ₂ physically farthest from the primary winding L ₁ becomes the highest.

Reference numeral 12 denotes a portion of a frit substrate on which an electronic component constituting an inverter circuit is mounted, such as a step-up transformer T.

5, specifically, a ferrite core 11 'having a structure in which a circumference 12b is made to penetrate from the center of the disk 11'a to the periphery of the disk 11'a is used, The secondary winding (pass coil) L ₃ and the primary winding (collector winding) L ₁ of the transformer T are wound adjacent to each other and further wound around the secondary winding L ₂ . Forward of the secondary winding (L ₂₎ has, starting from the vicinity of the primary winding (L ₁₎ ends at the outer peripheral edge of the circular plate (11a) of the ferrite core (11 ').

When _{one end} of the secondary winding L ₂ adjacent to the primary winding L ₁ is grounded, the voltage at the end of the secondary winding L ₂ physically farthest from the primary winding L ₁ becomes the highest.

In the step-up transformer T having the structure described above with reference to FIGS. 4 and 5, since no current flows through the secondary winding L ₂ at no load, the primary winding L ₁ of the transformer T is connected to the fourth A magnetic flux? 1 that passes through the entire length of a core (not shown) in the bobbin 11 is generated, as shown in Fig. On the other hand, when the load is connected, the secondary winding (L ₂ ) generates a magnetic field by the current flowing in the load. The direction of the magnetic flux? 2 by this magnetic field is opposite to the magnetic flux? 1 generated by the primary winding L ₁ as shown in FIGS. 4 (b) and 5 (c).

Thereby, the secondary winding (L ₂ ) is composed of a portion (L ₂₁ ) which functions as a secondary winding which is tightly coupled to the primary winding, and an inductive ballast which acts as a choke coil, (L ₂₂ ).

The bifurcation point varies depending on the severity of the load, and when the load becomes large, the bifurcation point moves to the end side when the load becomes small on the primary winding (L ₁ ) side.

A high voltage induced in the end portion of the secondary winding L ₂ is applied to the discharge tube DT as a load, but when the discharge tube DT is turned on and the current The current flowing through the discharge tube DT during the lighting is limited and the applied voltage is also lowered by the action of the inductive ballast, that is, the portion L ₂₂ operating as the choke coil. Thus, An ideal voltage / current characteristic necessary for lighting of the transistor is obtained.

The part L ₂₂ that is divided at the time of lighting the discharge tube DT and operates as a choke coil is inserted into the high frequency choke coil L _a of the impedance matching circuit 10 and the secondary winding of the winding transformer T The parasitic capacitance of the discharge tube L ₂ , and the parasitic capacitance generated around the discharge tube DT, and the like, to constitute the impedance matching circuit 10. By inserting this impedance matching circuit 10 between the winding transformer T and the discharge tube DT, the output of the secondary winding L ₂ is prevented from being reflected by the discharge tube DT and returned, because it can send the output of the winding (L _2), the efficiency in discharge tubes (DT) it may be better to light the discharge tubes (DT) with high luminance.

For example, assuming that the core diameter is 2 mm x 23 mm, the diameter is 0.04 mm, and the secondary winding is 4000 turns, the parasitic capacitance C ₃ generated in the secondary winding-connected portion L ₂₁ is about 10 pF And the equivalent resistance (R _a ) of the discharge tube DT made of a cold cathode fluorescent tube having a diameter of 3 Ø at 2 W at a driving frequency of 12 kHz is set to about 75 k OMEGA, the inductance component L (L) generated in the secondary winding sintered portion L _{22 a)} 80 and pre-Henry, and the parasitic capacitance generated in the vicinity of the discharge tubes (DT) (C) is 30pF (pico-farad) degree, but the above equation (1) to (3) under the conditions according trans side The impedance Zp can be matched and the power factor is improved even though the impedance Zp is a simple structure of only about 188 k.OMEGA.

The above embodiment shows a case where a winding transformer is used as the voltage boosting transformer. However, the voltage transformer is not limited to the winding transformer, and a piezoelectric transformer may be used.

Since the piezoelectric transformer is a mechanical vibration type, leakage flux is eliminated as compared with the winding transformer. Therefore, measures are not required and the material is made of non-burning ceramics.

FIG. 6 shows a schematic configuration of an inverter for a discharge tube constituted by using a piezoelectric transformer (Ta) as a step-up transformer. The piezoelectric transformer is a piezoelectric ceramic that is distorted by high-frequency driving of the piezoelectric ceramic sandwiched by electrodes, and a high electric charge voltage generated by this distortion is taken out by other electrodes including the same piezoelectric ceramics. In the figure, OS is a high-frequency oscillation circuit, 10 is an impedance matching circuit, and DT is a discharge tube.

7 shows a specific circuit example of the impedance matching circuit 10. The circuit 10 includes a high-frequency choke (hereinafter referred to as &_quot; high-frequency choke ") 10 inserted in series between one end of the secondary side of the piezoelectric transformer T _a and one end of the discharge tube DT, coil made of a (10b) and the storage capacitor (C ₆₎ π-type matching circuit consisting of a parasitic capacitance (C ₄₎ generated in the vicinity of the discharge tubes (DT). An integer can be determined by the same method as described above with reference to FIG. 3 so that the high-frequency choke coil 10b, the auxiliary capacitance C ₆ , and the parasitic capacitance C _{4 of this} circuit constitute an impedance matching circuit.

C _B in the secondary side equivalent circuit (T _a2 ) of the piezoelectric transformer shown in the figure is a structure in which the piezoelectric transformer basically has electrodes on both surfaces of the piezoelectric ceramic, and the piezoelectric transformer Although the equivalent capacitance of the capacitor (C _B), if the reactance is a large extent can not be ignored, the capacity (C _B) is also good as a π-type impedance matching circuit configured to put.

In the absence of the above-described impedance matching circuit 10, if reflection occurs due to impedance mismatching or the power factor deteriorates, a large amount of heat loss occurs due to dielectric loss or the like constituting the capacitance component of the piezoelectric transformer, do.

In order to constitute a liquid crystal backlight, a discharge tube made of a fluorescent tube is disposed as an edge light of a light guide for backlight illumination. In order to increase the light introduction efficiency of the light guide, The capacitance generated between the silver sheet and the ground is applied to the parasitic capacitance C ₄ of the discharge tube DT as shown in Fig. 8 (a) by the capacity partial pressure action of the secondary side capacity (C ₈₎ of (C ₄₎ and the piezoelectric transformer (T _a2), by reducing the voltage applied to the discharge tube (DT), thereby lowering the brightness of the discharge tube (DT) . However, when the impedance matching circuit 10 is inserted, this phenomenon does not occur, and the decrease in luminance due to the capacitive partial pressure action can be prevented.

Likewise, as shown in Fig. 8 (b), the same effect can be obtained by inserting the impedance matching circuit 10, even in the case of an electromotive-type tube having a very large characteristic capacity.

FIG. 1 is a principle drawing showing one embodiment of an inverter for a discharge tube according to the present invention,

FIG. 2 is a circuit diagram showing a specific circuit configuration in part of the first stage,

3 is a diagram for explaining a method of setting the circuit constants of the circuits in the second stage,

Fig. 4 (a) is an external perspective view, Fig. 4 (b) is a view showing the shape of a magnetic flux without load, and Fig. to be.

Fig. 5 is a perspective view showing the structure of another example of the leakage flux type winding transformer used as the step-up transformer in the second drawing. Fig. 5 (a) is an external perspective view, Respectively,

6 is a principle construction diagram showing one embodiment of an inverter for a discharge tube according to the present invention using a piezoelectric transformer;

FIG. 7 is a circuit diagram showing a specific circuit configuration of a portion of FIG. 6;

FIG. 8 is a view for explaining a conventional problem in the case of using a piezoelectric transformer,

FIG. 9 is a circuit diagram showing an example of a conventional inverter circuit for a discharge tube;

FIG. 10 is a graph for explaining a conventional problem.

DESCRIPTION OF THE REFERENCE NUMERALS to the main parts of the drawings "

DT: discharge tube OS: high-frequency oscillation circuit

T: Step-up transformer (winding transformer) Ta: Step-up transformer (piezoelectric transformer)

L ₁ : primary winding L ₂ : secondary winding

L ₂₁ : tightly coupled portion L ₂₂ : sintered portion

10: impedance-matching circuit 10 _a: high-frequency choke coil

10 _b : High frequency choke coil C ₃ : Secondary side parasitic capacitance

C ₄ : Parasitic capacitance C ₅ , such as a discharge tube, C ₆ : Auxiliary capacitance

As described above, according to the present invention, the discharge tube is connected to the secondary side of the step-up transformer through the impedance matching circuit, and the impedance of the load seen from the power source side matches the impedance of the power source side viewed from the load side, and the raised high- A part of the supplied power is not returned to the power source side and the lighting brightness of the discharge tube is not lowered even if the driving frequency is increased for miniaturization of the step-up transformer or the like.

In particular, a pi-type matching circuit is formed by the high-frequency choke coil inserted in series between the one end of the secondary side of the step-up transformer and one end of the discharge tube, and the parasitic capacitance generated around the secondary side parasitic capacitance of the step- The current limit is appropriately performed as an inductive ballast composed of a high frequency choke coil so that the voltage applied to the discharge tube is not lowered even if the parasitic capacitance of the discharge tube is large due to the use of the high frequency choke coil. Even if the parasitic capacitance of the discharge tube is increased, the voltage for applying the voltage to the discharge tube is lowered and the luminance of the discharge tube is not lowered.

In addition, the secondary winding of the winding transformer of the leakage magnetic flux type has at least one tightly coupled portion and a smallly-coupled portion tightly coupled to the primary winding, respectively, and the secondary side parasitic capacitance of the winding transformer and the inductive An impedance matching circuit is formed in accordance with an induction component formed in a sintered portion of the secondary winding and a parasitic capacitance of a discharge tube or the like and an auxiliary capacitance provided in an auxiliary manner so as to operate as a ballast and the impedance of the load seen from the power source side and the impedance The high frequency power that is matched and stepped up is reflected at the load side and a part of the supplied power does not return to the power source side. Therefore, even if the driving frequency is increased for the miniaturization of the step-up transformer or the like, the lighting brightness of the discharge tube is not lowered.

Further, in order to constitute the impedance matching circuit, it is necessary to eliminate the connection of the inductive ballast, and furthermore, the voltage is applied to the discharge tube at the high high frequency voltage which is boosted until the discharge tube lights up. After the discharge tube is turned on, So that it can supply one electric power.

In addition, since a circuit formed in accordance with the parasitic capacitance of the high-frequency choke coil and the discharge tube is used as the impedance matching circuit, the capacitance of the piezoelectric transformer is equivalent to that of the piezoelectric transformer It is possible to correct the capacity partial pressure action by the characteristic capacitance C _b and the parasitic capacitance C ₄ generated around the discharge tube to prevent the luminance reduction by the silver reflective sheet and to output the high voltage by the high step- The discharge lamp lighting current is not limited by the current limiting function based on the equivalent capacitance contained in the piezoelectric ceramics forming the conventional piezoelectric transformer after the lamp is turned on but the discharge lamp lighting current is controlled by the inductive ballast Limit. Since the impedance matching circuit is inserted, the impedance of the load seen from the power source side matches the impedance of the power source side from the load side, and the raised high frequency power is reflected from the load side so that a part of the supplied power does not return to the power source side.

Claims (4)

Frequency oscillating circuit and a step-up transformer for stepping up an output of the high-frequency oscillating circuit, and a discharge tube is connected to the secondary side of the step-up transformer, characterized in that the secondary side of the step- And an impedance matching circuit matching the impedance of the circuit and the discharge tube is connected. The variable resonator according to claim 1, wherein the impedance matching circuit comprises a high-frequency choke coil inserted in series between one end of the secondary side of the step-up transformer and one end of the discharge tube, and a parasitic capacitance generated around the secondary side parasitic capacitance of the step- And a? -Type matching circuit formed therein. The wind power transformer according to claim 1, wherein the step-up transformer comprises a primary winding and a winding transformer of a leakage magnetic flux type having a secondary winding having at least one tight coupling portion and a small coupling portion tightly coupled to the primary winding and the small coupling portion, , Wherein said impedance matching circuit comprises a secondary side parasitic capacitance of said winding transformer and an inductive component formed in a sintered portion of said secondary winding so as to act as an inductive ballast at the time of lighting of said discharge tube, And a matching circuit formed by a storage capacitor. The plasma display apparatus according to claim 1, wherein the step-up transformer is a piezoelectric transformer, and the impedance matching circuit is provided with an auxiliary capacitance, a high-frequency choke coil, and a matching capacitance formed by a parasitic capacitance of the discharge tube Circuit for a discharge tube.