JPH071697Y2 - Discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a discharge lamp lighting device.

[Prior Art] In recent years, in a discharge lamp lighting device, a semiconductor type discharge lamp lighting device has been introduced in order to solve the problems in size and weight of a so-called copper-iron type ballast mainly including a transformer and a choke coil. When considering a fluorescent lamp as a discharge lamp, by increasing the lighting frequency of the semiconductor discharge lamp lighting device to several tens of KHz, it is possible to improve the luminous efficiency (lm / W) in addition to the reduction in size and weight. It is designed and extremely effective.

On the other hand, when considering a high-pressure discharge lamp as a discharge lamp, if the lighting frequency of the semiconductor discharge lamp lighting device is increased to several tens KHz, basically the so-called acoustic resonance phenomenon causes arc instability and normal lighting occurs. However, it was necessary to devise some means to achieve normal lighting.

As one of the methods, there is a method in which the frequency itself of several tens KHz is used but the lighting frequency is finally set to a frequency equal to or lower than the frequency at which the acoustic resonance phenomenon occurs.

In this method, the lighting frequency is generally likely to fall within the audible frequency range. So the fundamental frequency of acoustic resonance generally exists at several KHz.

FIG. 3 shows an example of a circuit that realizes the above method. In this circuit, the AC power supply V ₁ is a diode bridge DB ₁ , a transistor Q ₀ , a choke coil L ₀ , a diode D ₀ ,
A so-called step-up chopper circuit 1 including a capacitor C ₀ converts alternating current into direct current and supplies the direct current to the inverter circuit 2.

The inverter circuit 2 includes transistors Q ₁ and Q ₂ that perform high frequency switching, and transistors Q ₃ and Q ₄ that perform low frequency switching at a frequency lower than the fundamental frequency of acoustic resonance.
As shown in FIG. 4 (a), the transistor Q ₁ is turned on and off at a high frequency only when the transistor Q ₃ is turned on.
Q ₄ is ON only when the transistor Q ₂ turns on and off at a high frequency, and and adapted to turn on and off the transistors Q _3, Q ₄ alternately. Switching control of these transistors Q _{1 to} Q ₄ and transistors of the boost chopper circuit 1
The control of Q ₀ is performed by the control unit 3. Each transistor
Connect a series circuit of choke coil L ₁ , discharge lamp DL and choke L ₂ between the connection point of Q ₁ and Q _{4 and} the connection point of transistors Q ₂ and Q ₃ , and further connect discharge lamp DL and choke coil. A capacitor C ₁ is connected in parallel to the series circuit of L ₂ and each transistor Q ₁
Diodes D _{1 to} D ₄ for freewheeling are connected in parallel to Q ₄ respectively.

Considering here the discharge lamp DL, the choke coil L ₂ , and the capacitor C ₁ as the load of the inverter circuit 2, the capacitor C ₀ , the transistor Q ₁ , the choke coil L ₁ , the above load, the transistor Q _{3 in the} ON state, and the diode D ₄ Circuit constitutes a chopper circuit, and the circuit of the capacitor C ₀ , the transistor Q ₂ , the choke coil L ₁ , the above load, the transistor Q _{4 in the} ON state and the diode D ₃ also constitutes a chopper circuit.
The current I _L1 flowing in the common choke coil L ₁ in the two chopper circuits alternates every time the transistors Q ₃ and Q ₄ are turned on. Therefore, the current I _L1 flowing in the choke coil L ₁ is not shown in FIG. 4 (b). It exhibits a waveform.

This current I _L1 is shunted to the capacitor C ₁ and the series circuit of the discharge lamp DL and the choke coil L ₂ . The capacitor C ₁ plays the role of a so-called high-pass filter, and is a choke coil.
L ₂ plays the role of a so-called low-pass filter. Therefore, the current I _C1 flowing through the capacitor C ₁ becomes a current mainly composed of high frequency components of the current I _L1 as shown in FIG. 4 (c), and the discharge lamp D
The current I _DL flowing in the series circuit of L and choke coil L ₂ is 4th
As shown in FIG. 7D, the current mainly consists of the low frequency component of the current _IL1 .

Since the circuit of FIG. 3 is constructed and operates as described above in this manner, a low-frequency current below the fundamental frequency of acoustic resonance flows through the discharge lamp DL, and arc instability due to acoustic resonance does not occur, On the other hand, since a high-frequency current flows through the choke coil L ₁ that is the current limiting element of the discharge lamp DL due to the switching of the transistors Q ₁ and Q ₂ , the required inductance value can be reduced and the discharge lamp lighting device can be made smaller and lighter. Is.

By the way, focusing on the mounting surface of the circuit shown in the figure, in the case of a device that lights a fluorescent lamp, the shape of the discharge lamp lighting device has a large degree of tolerance in the longitudinal direction due to the shape of the discharge lamp, but the target is a high pressure discharge lamp. When used as a load, it is required that the dimensions of the length, width, and height are as small as possible in view of the correlation with the shape of the discharge lamp. The mounting structure of the discharge lamp lighting device manufactured on such a premise has a structure as shown in FIG. 5, for example.

In this mounting example, the metal case 4 is divided into two parts by a metal plate 5, and printed circuit boards P ₁ and P ₂ on which circuit components are wired are installed on both sides of the metal plate 5. Here, in order to make the vertical, horizontal, and height dimensions of the case 4 as small as possible, _two printed circuit boards P ₁ and P _{2 on} which each circuit component is mounted are used.
As shown in the figure, the non-component mounting surfaces are back-to-back so as to face each other via the metal plate 5.

In this case, it is general to separate the circuit portion mainly composed of the step-up chopper circuit 1 used as a DC power source and the portion of the inverter circuit ₂ and mount them on the printed circuit boards P ₁ and P ₂ .

When the printed boards P ₁ and P ₂ are separated in this way, a metallic plate such as a metal plate 5 is used to reduce the return of electrical noise from the inverter circuit 2 to the AC power supply V ₁ . It is well known that it is effective to interpose between P ₁ and P ₂ as shown in the figure.

When the circuit of FIG. 3 is reviewed, it can be seen from the waveform diagram of FIG. 4 (b) that a current of audible frequency is flowing through the choke coil L ₂ . Since the choke coil L ₂ is a filter element as described above, the inductance value need not be so large, and a current having the same value as that of the discharge lamp DL flows, and the frequency of the current is a relatively low frequency. As the magnetic core of the choke coil L ₂ , an iron core 7 having an open magnetic circuit is usually used, or an air core is usually used.

[Problems to be Solved by the Invention] When the choke coil L ₂ is mounted on the printed circuit board P ₂ as shown in FIG. 5 as described above, the low-frequency leakage flux from the choke coil L ₂ is at least the metal plate. It will cross a large number of 5. This is shown in FIG. Due to this interlinking, an eddy current is generated in the metal plate 5, and a force in a direction of being attracted to or separated from the choke coil L ₂ acts on the eddy current path. Therefore, the electromagnetic force causes mechanical vibration in the metal plate 5 with the frequency of the current of the choke coil L ₂ as a fundamental frequency, and the frequency of the current of the choke coil L ₂ itself is in the audible range. The vibration appears as noise. The broken line in FIG. 6 conceptually shows the magnetic flux distribution from the iron core 6 of the choke coil L ₂ .

That is, an iron core or an air core having an open magnetic circuit is used as a magnetic core of an inductance element used at an audible frequency, and a metal plate is linked to many portions of the magnetic flux generated from the inductance element and flying out into the air. If it is necessary to install a metal plate 5 between the printed circuit boards P ₁ and P ₂ for electromagnetic shielding as shown in FIG. _{When the} metal plate 5 is brought close to ₁ and P ₂ , there is a problem that noise increases.

The present invention has been made in view of the above problems, and an object thereof is to provide a discharge lamp lighting device capable of reducing noise by simple modification.

[Means for Solving the Problems] The present invention includes an inverter circuit having an inductance element that operates at least at an audible frequency, uses a magnetic core having an open magnetic path as a magnetic core of the inductance element, and uses a circuit component. In a discharge lamp lighting device in which a component is mounted on at least two printed circuit boards and the component-non-mounting surfaces of both printed circuit boards face each other through a metallic plate disposed between the printed circuit boards. A hole is provided in the portion of the metallic plate facing at least the maximum area portion of the inductance element corresponding to the surface direction of the flexible plate.

[Function] Since a hole is provided in the portion of the metallic plate where the magnetic flux generated from the inductance element should be concentrated and interlinked, the concentrated magnetic flux interlinking with the metallic plate is eliminated, Therefore, a large eddy current does not flow in that part,
Therefore, the attractive repulsive force of the metallic plate itself due to the magnetic flux generated by the inductance element becomes extremely small, and the noise can be reduced.

[Embodiment] The present invention will be described below with reference to an embodiment. In the present embodiment, the second
Using the circuit shown in the figure, the mounting structure is basically similar to that of FIG. 4, but a hole 7 larger than the maximum area of the choke coil L _{2 which} is an inductance element facing in the plane direction of the metal plate 5 is provided facing the metal plate 5. It is provided at the part as shown in FIG. Of course, the hole 7 may be a notch-shaped hole shown in the drawing or a normal hole.

Thus, since the holes 7 are provided in the portion of the metal plate 5 where the magnetic flux generated from the choke coil L ₂ is concentrated and should be linked, the concentrated linkage to the metal plate 5 is eliminated. Therefore, a large eddy current does not flow in this portion, so that the attractive repulsive force of the metal plate 5 itself caused by the leakage magnetic flux from the choke coil L _{2 which is an} inductance element becomes extremely small, and the noise can be reduced.

Since the present invention focused on the fact that the frequency of the current flowing through the choke coil L ₂ was extremely low and that the noise itself propagated from the choke coil L ₂ to the printed circuit board P ₁ side was small, the metal plate 5
Regarding the power supply feedback noise component coming to the printed circuit board P ₁ side, which is the original installation purpose of, even if the hole 7 is provided only in the portion facing the choke coil L ₂ , the electromagnetic shielding effect of the metal plate 6 is hardly deteriorated. It goes without saying that it is a thing.

For measures against the influence on the case 4 by the magnetic flux from the choke coil L ₂ , check the choke coil L ₂ and the case 4.
It is good to keep a distance between each side of
If it becomes necessary to dispose the choke coil L _{2 in the} vicinity of the case 4, even if a hole 7 similar to the metal plate 5 is provided in the case 4 portion where the leakage magnetic flux from the choke coil L ₂ is concentrated and interlinked. Of course, the same effect can be obtained from the viewpoint of noise.

[Advantages of the Invention] In the discharge lamp lighting device configured as described above, the present invention provides a hole in a portion of the metallic plate facing at least the maximum area portion of the inductance element corresponding to the surface direction of the metallic plate. Since there is no interlinkage of the leakage magnetic flux from the concentrated inductance element on the metallic plate, a large eddy current does not flow in the relevant part, and the attractive magnetic repulsion of the metallic plate itself due to the leakage magnetic flux of the inductance element. The force is extremely small, and the noise can be reduced.

[Brief description of drawings]

FIG. 1 is a partially broken perspective view of an embodiment of the present invention, FIG. 2 is a front view of a metal plate of the same, FIG. 3 is a circuit diagram of a discharge lamp lighting device, and FIG. Waveform diagram, FIG. 5 is a partially broken perspective view of the conventional example, and FIG. 6 is an operation explanatory diagram of the same as above. Reference numeral 5 is a metal plate, 7 is a hole, L ₂ is a choke coil, and P ₁ and P ₂ are printed circuit boards.

Claims (1)

[Scope of utility model registration request] 1. An inverter circuit having an inductance element that operates at least at an audio frequency,
A magnetic core having an open magnetic circuit is used as the magnetic core of the above-mentioned inductance element, and the circuit components used are divided and mounted on at least two printed circuit boards, and a metallic plate disposed between both printed circuit boards is used. In the discharge lamp lighting device in which the component non-mounting surfaces of both printed circuit boards are opposed to each other, in the portion of the metallic plate facing at least the maximum area portion of the inductance element corresponding to the surface direction of the metallic plate. A discharge lamp lighting device comprising a hole.