WO2006046405A1

WO2006046405A1 - Discharge lamp lighting apparatus

Info

Publication number: WO2006046405A1
Application number: PCT/JP2005/018797
Authority: WO
Inventors: Hiroshi Shinmen; Robert Weger
Original assignee: Minebea Co., Ltd.
Priority date: 2004-10-27
Filing date: 2005-10-12
Publication date: 2006-05-04
Also published as: JP2008041249A

Abstract

A discharge lamp lighting apparatus wherein the tube current can be stabilized at a low cost without providing any ballast elements on the secondary side of an inverter transformer. A discharge lamp lighting apparatus (10) comprises inverter means (12) and an inverter transformer (TR). A discharge lamp (La), such as a cold cathode tube or the like, is connected directly to a secondary winding (16) of the inverter transformer (TR) with no ballast elements therebetween. The inverter means (12) includes switching means (13), and an inductor (18) serving as a ballast impedance element is series connected directly between the switching means (13) and a primary winding (14) of the inverter transformer (TR). The inductor (18) is connected not to the secondary side of the inverter transformer to which a high voltage is applied but to the primary side of the inverter transformer, so that no withstand high-voltage elements must be used, the costs of the components can be reduced, and the safety of the apparatus can be enhanced.

Description

Specification

Discharge lamp lighting device

Technical field

TECHNICAL FIELD [0001] The present invention relates to a discharge lamp lighting device, and more particularly to a discharge lamp lighting device that lights a cold cathode tube used as a light source for a backlight of a liquid crystal display device.

Background art

Conventionally, discharge lamps such as cold cathode tubes have been widely used as light sources for backlights of liquid crystal display devices. Generally, such discharge lamps are used by discharge lamp lighting devices having an inverter. AC lights up. Such a discharge lamp lighting device usually has an inverter transformer for generating a high voltage on the secondary side, and an inverter means for generating a high frequency voltage is connected to the primary side of the inverter transformer, and the secondary side is connected. On the side, a so-called ballast element, for example, a ballast capacitor, for stabilizing the tube current of the discharge lamp and the discharge lamp having negative resistance characteristics is connected. In such a circuit configuration, in order to obtain the tube voltage necessary for lighting the discharge lamp, it is necessary to generate an output voltage including the voltage drop of the ballast capacitor connected in series with the discharge lamp on the secondary side. As a result, the size of the inverter transformer has increased, which has hindered the downsizing of equipment. For this reason, it has been proposed to eliminate the last capacitor by providing a low-voltage constant current source on the primary side of the inverter transformer and supplying electric power from the low-voltage constant current source. 1).

FIG. 6 is a circuit configuration diagram of the cold cathode tube lighting device described in Patent Document 1. This cold-cathode tube lighting device includes a voltage resonance type Royer circuit including an inverter transformer 1, transistors 2 and 3, resistors 4 and 5, a capacitor 6, and a choke coil _7, and a low-voltage constant current source 9. Thus, the cold cathode tube 8 is directly connected to the secondary side of the inverter transformer 1. This cold-cathode tube lighting device maintains constant tube current without connecting a ballast capacitor to the secondary side of the inverter transformer 1 by supplying power from the constant current source 9 to the inverter transformer 1.

Patent Document 1: Patent No. 3256992 Specification

Disclosure of the invention Problems to be solved by the invention

[0004] However, since a constant voltage power supply that is common to a liquid crystal drive circuit or the like is generally used as a power source for a discharge lamp lighting device used as a backlight of a liquid crystal display, a constant current is supplied to the discharge lamp lighting device. Using a source means adding new components to the liquid crystal display device, increasing the overall cost of the device.

[0005] In view of the above problems, an object of the present invention is to provide a discharge lamp lighting device capable of reducing the tube current stability without providing a ballast element on the secondary side of an inverter transformer at low cost. .

Means for solving the problem

[0006] In order to achieve the above object, the present invention includes an inverter means for outputting a high-frequency voltage and an inverter transformer, and the inverter means connected to a primary side of the inverter transformer is used to provide a secondary of the inverter transformer. In the discharge lamp lighting device for lighting the discharge lamp connected to the side, the inverter means includes a switching means, and a ballast impedance element is connected in series between the switching means and the primary winding of the inverter transformer. It is characterized by being.

[0007] Further, the ballast impedance element is constituted by a resistor, a capacitor, an inductor, or a combination thereof, or a combination thereof.

[0008] Further, the switching means is constituted by a full bridge circuit, and the full bridge circuit is driven by separately excited oscillation.

[0009] In one aspect of the present invention, the discharge lamp lighting device according to the present invention further includes a protection circuit and a current detection circuit.

Here, the protection circuit may detect an output voltage of a tertiary winding wound around the inverter transformer, or may be a ballast connected to a primary side of the inverter transformer. The voltage between the impedance element and the primary winding of the inverter transformer may be detected.

[0011] Further, the current detection circuit may detect a tube current flowing in the discharge lamp, or may detect a current flowing in a current transformer. Alternatively, the current on the low voltage side of the secondary winding of the inverter transformer may be detected. The invention's effect

[0012] According to the discharge lamp lighting device of the present invention, the last impedance element is connected in series between the switching means and the primary winding of the inverter transformer, so that the ballast element is connected to the secondary side. Therefore, it is possible to realize a discharge lamp lighting device that can stabilize the tube current without increasing the number of parts from the conventional configuration. In the present invention, the ballast impedance element is connected not to the secondary side of the inverter transformer to which a high voltage is applied, but to the primary side. This reduces the risk of failure and fire due to element breakdown, and increases the safety of the equipment. Further, since it is not necessary to connect a ballast element in series with the discharge lamp on the secondary side of the inverter transformer, the output power of the inverter transformer can be kept low. In addition, even when a short circuit between wires (so-called rare short) occurs on the secondary side of the transformer, the primary current ballast impedance element suppresses overcurrent flowing in the wire and prevents smoke and ignition of the inverter transformer. Can do.

[0013] In particular, when an inductor is used as the ballast impedance element, the inductance can be made smaller than when the inductor is connected to the secondary side, so that the ballast impedance element can be reduced in size. In addition, since the higher-order harmonic components are suppressed by the primary-side inductor, the input waveform force applied to the inverter transformer can also eliminate noise, and the heat generation of the transformer due to the harmonic components is suppressed. As a result, heat generation in the transformer is reduced.

[0014] Further, by making the inverter means a separately excited type, an element having any appropriate impedance that does not consider the influence on the resonance frequency on the primary side is selected as the no << last impedance element according to the present invention. be able to. In particular, a high-efficiency operation is possible by making the switching means a full-bridge circuit.

Brief Description of Drawings

FIG. 1 is a circuit configuration diagram showing a first embodiment of a discharge lamp lighting device according to the present invention.

FIG. 2 is a circuit configuration diagram showing inverter means of the discharge lamp lighting device according to the first embodiment of the present invention.

FIG. 3 is a circuit configuration diagram showing a second embodiment of a discharge lamp lighting device according to the present invention. FIG. 4 is a graph schematically showing an asymmetric voltage waveform by the inverter means in the second embodiment of the present invention.

FIG. 5 is a circuit configuration diagram showing a third embodiment of a discharge lamp lighting device according to the present invention.

FIG. 6 is a circuit configuration diagram showing a conventional discharge lamp lighting device.

Explanation of symbols

[0016] 10, 30, 40 Discharge lamp lighting device

12 Inverter means

13 Switching means (full bridge circuit)

18, 32, 43 Ballast impedance element

TR inverter transformer

La discharge lamp

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of a discharge lamp lighting device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit configuration diagram showing an embodiment of a discharge lamp lighting device according to the present invention. In FIG. 1, a discharge lamp lighting device 10 includes an inverter means 12 and an inverter transformer TR, and a discharge lamp La such as a cold cathode tube passes through a ballast element on a secondary winding 16 of the inverter transformer TR. Connected directly without. The inverter means 12 includes a switching means 13, and an inductor 18 is connected in series as a ballast impedance element in the present embodiment between the switching means 13 and the primary winding 14 of the inverter transformer TR. Yes.

In the present embodiment, the inverter unit 12 includes a full bridge circuit that is the switching unit 13 and a control circuit 21 that drives the full bridge circuit 13. As shown in Fig. 2, the full-bridge circuit 13 includes a pair of switching elements Ql and Q3 connected in series and a pair of switching elements Q2 and Q4 connected in series in parallel. For example, switching elements Q3 and Q4 are composed of NMOSFETs, and switching elements Ql and Q2 are composed of PM OSFETs. According to the gate voltage output from the control circuit 21, the inverter means 12 alternately turns on / off the switching element pairs (Ql, Q4) and (Q2, Q3) at a predetermined frequency (for example, about 60 kHz). High frequency voltage is generated at output terminals A and B. · ¾: Things.

In addition to the above-described components, the discharge lamp lighting device 10 shown in FIG. 1 includes a dimming circuit 22, a current detection circuit 23, and a protection circuit 24. The functions of the circuits 22 to 24 are as follows. It is as follows. First, the current detection circuit 23 generates an appropriate signal according to the current value detected by the current transformer 25 and outputs the signal to the control circuit 21, whereby the control circuit 21 is included in the inverter means 12, for example. The on-duty of the switching elements Q1 to Q4 to be varied is adjusted to adjust the power input to the inverter transformer TR. The protection circuit 24 generates an appropriate signal according to the voltage detected by the tertiary winding 26 of the inverter transformer TR and outputs the signal to the control circuit 21, so that the control circuit 21, for example, of the discharge lamp La When an abnormality such as open or short is detected, the operation of the inverter means 21 is stopped to protect the device. Further, the voltage between the inductor 18 that uses the tertiary winding 26 and the primary winding 14 of the inverter transformer TR may be detected. The dimming circuit 22 outputs a signal for adjusting the luminance of the discharge lamp La to the control circuit 21 by, for example, burst dimming, and thus the control circuit 21 has, for example, 150 to 30 OHz. The average brightness of the discharge lamp La is adjusted by intermittently operating the inverter means 12 at a certain frequency. In the example shown in the figure, the current detection circuit 23 detects the tube current of the power discharge lamp La in which the current is detected by the current transformer 25. The current flowing to the low voltage side of the secondary winding 16 of the inverter transformer TR May be detected.

[0020] The discharge lamp lighting device 10 according to the present embodiment includes an inductor 18 on the primary side of the inverter transformer TR, and the inductor 18 functions as a ballast impedance element, thereby stabilizing the tube current of the discharge lamp La. It is what realizes a kite. That is, if the tube current (hereinafter also referred to as secondary current) increases for some reason, the current (hereinafter also referred to as primary current) flowing through the primary winding 14 of the inverter transformer TR increases. Since the voltage applied by means 1 and 2 is constant, the impedance of inductor 18 acts to reduce the primary side current and lower its drop voltage, and consequently suppress the increase in secondary side tube current. Is done. Similarly, when the tube current decreases, the primary side current also decreases. At this time, the impedance of the inductor 18 acts to increase the primary side current and increase the voltage drop. As a result, the secondary side tube current increases. A decrease in current is suppressed. Where Assuming that the power ratio of the inverter transformer TR (number of secondary windings Z number of primary windings) is n and the equivalent load resistance of the discharge lamp La is R, see from the primary side of the inverter transformer TR. Since the load impedance is RZn ² , the impedance required for the ballast impedance element must be an appropriate value for RZn ² .

[0021] The present invention is not limited to the type of impedance element to be used. As the ballast impedance element according to the present invention, it is preferable that any of a resistor, a capacitor, an inductor, or a combination thereof can be used. As in the ballast impedance element in the present embodiment, an inductor or a combination including an inductor is used. In the discharge lamp lighting device according to the present invention, since the last impedance element is connected to the primary side of the inverter transformer, it is not necessary to use a high withstand voltage element. The inductor can be advantageously used as a ballast element while overcoming the conventional drawback that the shape of a high voltage resistant inductor is large. In addition, as described above, since the load impedance viewed from the primary side of the inverter transformer is as small as about 1 Zn ² , the discharge lamp lighting device 10 in the present embodiment has an inductor having the same function as the nost element. Compared to the case of connecting to the secondary side, the inductance can be reduced to about LZn ² and the element can be further downsized. For example, in the discharge lamp lighting device 10, if the wiring ratio n of the inverter transformer TR is 100 and the inductance L of the inductor 18 is about 30 μΗ, an inductor having an inductance L of about 300 mH is used as the ballast element on the secondary side. It will perform the same function as when connected to.

As in the circuit configuration shown in FIG. 6, even in the conventional discharge lamp lighting device, the force that includes the choke coil 7 on the primary side of the inverter transformer 1 Unlike the ballast impedance element according to the invention, it is connected between the switching means constituted by the transistors 2 and 3 and the DC power source 9, and only when an overcurrent flows instantaneously due to, for example, magnetic saturation of the inverter transformer 1 or the like. It functions as an impedance element, and is provided to protect the transistors 2 and 3 from being damaged. It functions as a ballast element that stabilizes the tube current by dividing the high-frequency voltage generated by the switching means. It is something that does not. In the present embodiment, since the inductor 18 functions as a low-pass filter, a voltage waveform applied to the primary winding 14 of the inverter transformer TR by cutting a harmonic component of the output voltage of the inverter means 12 is cut. Can be approximately sinusoidal. As a result, noise is removed from the inverter transformer TR and heat generation of the inverter transformer TR due to harmonic components is suppressed.

[0024] Next, as one of the advantages of connecting a ballast impedance element on the primary side, the operation when a short-circuit between wires (so-called rare short) occurs on the secondary side of the inverter transformer TR will be described. . When a short-circuit occurs on the secondary side of the inverter transformer, the secondary circuit connects the resistance Rs of the shorted portion of the secondary conductor to the secondary side regardless of the impedance of the discharge lamp and ballast element. Therefore, in the conventional discharge lamp lighting device, an excessive current flows through the inverter transformer, causing smoke and fire. At this time, if the primary side voltage of the inverter transformer is Vp and the load resistance due to rare short is Rp, the resistance value when viewed from the primary side is Rp.

P = Vp ² / Rp

It is represented by However, since the discharge lamp lighting device 10 according to the present embodiment includes the ballast impedance element (in this case, the inductor) 18 on the primary side, the loss P in the short-circuit portion is

P = Rp .Vp ² / ((co L) ² + Rp ² )

(Where L is the inductance of inductor 18), and it can be seen that the impedance of inductor 18 suppresses heat loss, that is, heat generation due to overcurrent.

[0025] In the discharge lamp lighting device 10 according to the present embodiment, the inverter means 12 is configured by a high-efficiency separately-excited circuit composed of a full bridge circuit 13 and a control circuit 21, and the full bridge circuit 13 is controlled. The circuit 21 is driven at a predetermined frequency. Therefore, for example, unlike the case of the Royer circuit in which the drive frequency of the inverter means is determined by the resonance frequency of the LC resonance circuit provided on the primary side of the inverter transformer 1 as shown in FIG. It is possible to connect an element having an arbitrary impedance suitable as a ballast without considering the influence on the primary pole j.

[0026] Hereinafter, another embodiment of the present invention will be described with reference to FIGS. Throughout the description, the same components as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof will be omitted as appropriate, and only the differences will be described.

FIG. 3 is a circuit configuration diagram showing a second embodiment of the discharge lamp lighting device according to the present invention. The discharge lamp lighting device 30 in this embodiment is substantially the same as the discharge lamp lighting device 10 in the first embodiment described above, but is connected between the inverter means 12 and the primary winding 14 of the inverter transformer TR. As a ballast impedance element, a series circuit 32 including a capacitor 34 and an inductor 33 is connected.

[0028] The discharge lamp lighting device 30 in the present embodiment has the following operations in addition to the same operations and effects as the discharge lamp lighting device 10 in the first embodiment described above. For example, as shown in FIG. 4, when the output waveform of the inverter means 12 has an asymmetry such that the voltage in one direction is V and the voltage in the other direction is V + Δν, the output voltage is averaged. Therefore, a DC voltage of Δν ′ (where Δν ′ is a time average of Δν) is superimposed. For this reason, if the ballast impedance element is only the inductor 33, a large direct current is superimposed on the inverter transformer TR, causing magnetic saturation and a decrease in efficiency. At this time, the discharge lamp lighting device 30 adds a capacitor 34 connected in series to the inverter means 12 to the ballast impedance element, thereby cutting off the DC component of the asymmetric voltage waveform, and the primary voltage of the inverter transformer TR. This improves the symmetry of the voltage applied to line 14.

FIG. 5 is a circuit configuration diagram showing a third embodiment of the discharge lamp lighting device according to the present invention. The discharge lamp lighting device 40 in the present embodiment has a capacitor 44 connected in parallel to the primary winding 14 of a power inverter transformer TR that is substantially the same as the discharge lamp lighting device 10 in the first embodiment described above. In that respect, it is different.

The discharge lamp lighting device 40 in the present embodiment has the following operations in addition to the same operations and effects as the discharge lamp lighting device 10 in the first embodiment described above. In other words, a resonance circuit is formed on the secondary side of the inverter transformer TR by the parasitic capacitance between the discharge lamp and the liquid crystal display device and the self-inductance on the secondary side of the inverter transformer TR. When the tube current is not stable with respect to the frequency, a condenser having an appropriate capacity, such as the discharge lamp lighting device 40 in the present embodiment, is used. By connecting the capacitor 44 in parallel with the primary wire 14 of the inverter transformer, the tube current can be stabilized. Further, the combination of the inductor 43 and the capacitor 44 cuts the harmonic component of the output voltage of the inverter means 12 more effectively, and the voltage waveform applied to the primary winding 14 of the inverter transformer TR is almost sinusoidal. It can be.

Claims

The scope of the claims

[1] A discharge lamp that includes an inverter means that outputs a high-frequency voltage and an inverter transformer, and that turns on a discharge lamp connected to the secondary side of the inverter transformer by the inverter means connected to the primary side of the inverter transformer In the lighting device,

The discharge lamp lighting device, wherein the inverter means includes switching means, and a ballast impedance element is connected in series between the switching means and a primary winding of the inverter transformer.

[2] The discharge lamp lighting device according to [1], wherein the ballast impedance element is configured by any one of a resistor, a capacitor, and an inductor, or a combination thereof.

[3] The discharge lamp lighting device according to claim 1 or 2, wherein the switching means is configured by a full bridge circuit, and the full bridge circuit is driven by separately excited oscillation.

[4] The discharge lamp lighting device according to any one of claims 1 to 3, further comprising a protection circuit and a current detection circuit.

5. The discharge lamp lighting device according to claim 4, wherein the protection circuit detects an output voltage of a tertiary winding wound around the inverter transformer.

6. The discharge circuit according to claim 4, wherein the protection circuit detects a voltage between a ballast impedance element connected to a primary side of the inverter transformer and a primary winding of the inverter transformer. Electric light lighting device.

[7] The discharge lamp lighting device according to any one of claims 4 to 6, wherein the current detection circuit detects a current flowing through a current transformer.

[8] The discharge lamp lighting device according to any one of claims 4 to 6, wherein the current detection circuit detects a tube current flowing through the discharge lamp.

9. The discharge lamp lighting device according to any one of claims 4 to 6, wherein the current detection circuit detects a current on a low voltage side of the secondary winding of the inverter transformer.