JP4293815B2 - Electronics - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic apparatus in which a circuit on a circuit board on which a circuit that generates noise and a digital circuit are mounted is shielded by a plurality of shield cases.
[0002]
[Prior art]
In a monitor device provided with a liquid crystal display device, a backlight is provided on the back of the liquid crystal display device.
[0003]
Since a fluorescent lamp is used as the backlight, a backlight drive circuit for driving the fluorescent lamp is mounted on a circuit board provided in the monitor device. However, the backlight drive circuit is provided with an inverter circuit that converts a direct current input into a high-voltage alternating current and applies it to a fluorescent lamp, and is therefore a source of radiation noise (EMI (Electro Magnetic Interference)). Therefore, it is necessary to cover the backlight drive circuit with a shield case and electromagnetically shield it so that the radiation noise does not affect the digital video signal processing circuit or the like. A technique for electromagnetically shielding a circuit that generates radiation noise is described in, for example, Patent Document 1 below.
[0004]
However, in a small device such as an in-vehicle monitor device, the backlight driving circuit and the digital video signal processing circuit may be mounted on the same circuit board. In this case, the backlight driving circuit on the circuit board is covered with a small shield case to be electromagnetically shielded, and the circuit board is further covered with a shield case larger than the small shield case, so that the digital image can be obtained from an external electric circuit. It is necessary to shield the signal processing circuit from being affected by noise.
[0005]
[Patent Document 1]
JP 2001-148586 A [0006]
[Problems to be solved by the invention]
However, in the structure in which the source of radiation noise is covered with a small shield case and the large shield case covers both the small shield case and the digital processing circuit, the large shield case is made sufficiently large. It is necessary not to interfere with the small shield case located inside. Therefore, the large shield case becomes unnecessarily large, which hinders downsizing and thinning of the device.
[0007]
SUMMARY OF THE INVENTION The present invention is to solve the above-described conventional problems. In an electronic apparatus using a circuit board on which a circuit that becomes a noise generation source and a circuit that requires another shield are mounted, the shield structure is thin. The purpose is to become.
[0008]
[Means for Solving the Problems]
The present invention, the circuit board and the circuit board having electronic components mounted, a first shield case covering a part of the electronic components mounted on the circuit board, which is not covered in the previous SL first shield case In an electronic device provided with a second shield case covering the electronic component above,
The first shield case and the second shield case both have a ceiling surface facing the circuit board and a side surface perpendicular to the ceiling surface, and the side surface rises from the circuit board,
The second shield case is provided with an opening that opens to the ceiling surface, and a plurality of folded pieces that are bent from the ceiling surface toward the circuit board with an edge of the opening as a fold. The first shield case enters the opening and is surrounded by the plurality of folded pieces, and the surface of the ceiling surface of the first shield case is flush with the surface of the ceiling surface of the second shield case. Position to,
Either one of the side surface of the first shield case and the folded piece is provided with an elastic piece, and the elastic piece is pressed against the other, and the first shield case and the second shield case are electrically connected. It is characterized by that.
[0009]
In the electronic device of the present invention, since the first shield case is exposed in the opening provided in the second shield case, there is no overlap between the first shield case and the second shield case. The space on the circuit board can be used effectively, the second shield case can be made small, and the entire electronic device can be thinned.
[0010]
In the electronic device of the present invention, the depth dimension from the circuit board to the upper surface of the second shield case can be minimized, and the electronic device can be made thinner.
[0012]
As described above, by elastically pressing the elastic piece and the opposing surface, the first shield case and the second shield case can be reliably set to the same potential.
[0013]
In this case, one or more gaps are provided between the first shield case and the second shield case, and the longest linear distance of the gap is 25 mm or less. preferable.
[0014]
When the digital processing circuit is electromagnetically shielded to reduce the influence of external noise, it is necessary to assume that the processing frequency of the electronic circuit serving as a noise generation source outside the shield case is up to about 1 GHz. When the processing frequency is 1 GHz, the wavelength of noise generated by passing through the space from this external circuit is 30 cm. However, when considering even harmonics with a wavelength of 1/12, shield a wavelength of 25 mm as external noise. is required. Therefore, the dimension is preferably 25 mm or less.
[0015]
For example, the present invention is effective when a circuit that becomes a noise generation source and a digital circuit are mounted on the circuit board and the circuit that becomes the noise generation source is covered with the first shield case. It is.
[0016]
In this case, the circuit that becomes the noise generation source is applicable to an electronic device that is a backlight drive circuit of a display device, and the digital circuit is a digital video signal processing circuit that drives the display device.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
1 is a perspective view showing a display unit as an embodiment of the electronic apparatus of the present invention, FIG. 2 is an exploded perspective view of the display unit, FIG. 3 is a cross-sectional view of the display unit taken along line III-III in FIG. It is a top view which shows the relationship between the opening part seen from the arrow IV direction of FIG. 2, and a 1st shield case.
[0018]
A display unit 1 shown in FIG. 1 is built in an in-vehicle display device or the like. The display unit 1 is assembled as one unit in a state where the liquid crystal panel 4, the backlight device, and the circuit board 7 are overlapped and the back portion is covered with the second shield case 3.
[0019]
A front frame 2 is provided at the front of the display unit 1, and a liquid crystal panel 4 is installed inside the front frame 2. A fluorescent lamp 5 and a light guide member 6 are provided on the back of the liquid crystal panel 4 as a backlight device.
[0020]
The liquid crystal panel 4 is a transmissive panel such as an STN (Super Twisted Nematic) liquid crystal panel. The fluorescent lamp 5 is a hot cathode tube or a cold cathode tube, and the light guide member 6 is formed of a transparent resin plate such as acrylic. Light from the elongated fluorescent lamp 5 is incident from the side surface of the light guide member 6 and becomes a uniform surface light source due to irregular reflection of light in the light guide member 6, and the liquid crystal panel 4 is illuminated from the back side.
[0021]
A circuit board 7 is overlaid on the back surface of the light guide member 6. On the back surface of the circuit board 7, various electronic components constituting a power supply circuit 8, a driver circuit 9 for driving the liquid crystal panel 4, a backlight driving circuit 10 for lighting the fluorescent lamp 5, and the like are mounted. . The power supply circuit 8 is, for example, a DC / DC converter that converts the battery voltage 24 [v] into a stable DC 5 [v] voltage when it is used in a vehicle. The driver circuit 9 is a digital video signal processing circuit for driving the liquid crystal panel 4. The backlight drive circuit 10 includes an inverter circuit that converts a DC input from a battery into an AC high voltage output.
[0022]
A small first shield case 11 is provided on the back surface of the circuit board 7 to cover the entire backlight drive circuit 10 or an inverter circuit that is a source of radiation noise.
[0023]
The first shield case 11 is formed in a box shape by pressing a conductive metal plate such as a plated steel plate. The first shield case 11 has a planar ceiling surface (upper surface) 11A facing in parallel with the circuit board 7, side surfaces 11D and 11D facing in the X direction, and side surfaces 11E and 11F facing in the Y direction. Further, an inclined side surface 11B is provided between the ceiling surface 11A and the side surface 11E.
[0024]
A total of six elastic pieces 11b formed by cutting and raising a part of the plate material constituting the first shield case 11 are provided on the side surfaces 11D, 11D, the side surface 11F, and the inclined side surface 11B. These elastic pieces 11b have a rectangular shape, are continuous with the first shield case 11 on the ceiling surface 11A, have a free end on the circuit board 7 side, and are spread outward.
[0025]
A plurality of locking pieces 11c are integrally provided at the lower ends of the side surfaces 11D, 11D, 11E, and 11F, and the locking pieces 11c are inserted into locking holes 7a formed in the circuit board 7, The locking piece 11 c is soldered to the conductive pattern formed on the circuit board 7.
[0026]
The second shield case 3 is pressed into a box shape with a conductive metal material such as a plated steel plate or an aluminum plate, and faces the ceiling surface 3B facing the circuit board 7 in parallel with the X direction. Side surfaces 3D and 3D, and side surfaces 3E and 3F facing each other in the Y direction. The inclined side surface 3a is between the ceiling surface 3B and the side surface 3E, and the inclined side surface 3b is between the ceiling surface 3B and the side surface 3F. Is provided.
[0027]
A rectangular opening 3A is formed in the ceiling surface 3B. The opening 3A has an area slightly larger than the ceiling surface 11A of the first shield case 11 and opens. As shown in FIG. 2, the second shield case 3 is provided with three folding pieces 3c, 3c, 3c bent at a right angle from the ceiling surface 3B toward the inside of the opening 3A. When the entire circuit board 7 is covered with the second shield case 3, the first shield case 11 enters the opening 3A, and each of the plurality of elastic pieces 11b provided in the first shield case 11 The first shield case 11 and the second shield case 3 are brought into contact with each other and have the same potential by being pressed against the inner surfaces of the folded pieces 3c, 3c, 3c and the inclined side surface 3a.
[0028]
In this embodiment, the inner surfaces of the three folded pieces 3c, 3c, 3c and the inclined side surface 3a function as opposing surfaces to which the elastic pieces 11b are elastically pressed. On the contrary, elastic pieces are provided on the folded pieces 3c, 3c, 3c and the inclined side surface 3a of the second shield case 3, and the elastic pieces are elastically pressed on the outer surface of the first shield case 11. May be. Further, since the folded pieces 3c, 3c, 3c are positioned so as to surround the first shield case 11, the backlight drive circuit 10 includes the first shield case 11 and the folded piece 3c. , 3c and 3c are double shielded.
[0029]
As shown in FIG. 3, the second shield case 3 covers the first shield case 11, the power supply circuit 8, and the driver circuit 9, and the second shield case 3 and the circuit board 7 are fixed. Alternatively, the display unit 1 is completed by fixing the second shield case 3 and the front frame 2. In addition, at least one of the first shield case 11 and the second shield case 3 is electrically connected to the ground pattern of the circuit board 7, and the first shield case 11 and the second shield case 3 are grounded. .
[0030]
As shown in FIG. 3, in the display unit 1, the ceiling surface 11A of the first shield case 11 is located in the opening 3A of the second shield case 3, and the ceiling surface 11A is the second shield. It is substantially coincident with the ceiling surface 3B of the case 3, or is slightly lower than the ceiling surface 3B or slightly higher than the ceiling surface 3B. Accordingly, there is no overlapping portion between the ceiling surface 3B and the ceiling surface 11A, and there is no need to provide a clearance in the overlapping portion between the ceiling surface 3B and the ceiling surface 11A, so that the height from the surface of the circuit board 7 to the ceiling surface 3B is high. The size can be reduced, and the entire display unit 1 can be made thin.
[0031]
In particular, in this display unit 1, since the second shield case 3 functions as a bracket that covers the entire back side of the unit, the second shield case is used to make the entire display unit 1 sturdy. 3 is preferably formed of a thick plate. Even in such a case, by positioning the ceiling surface 11A of the first shield case 11 within the plate thickness dimension of the second shield case 3, the depth dimension in the back direction of the unit can be reduced, and the unit is made thinner. it can.
[0032]
Further, since the first shield case 11 and the second shield case 3 are elastically pressed by the elastic piece 11b, both shield cases can be reliably brought into contact with each other to have the same potential.
[0033]
In this display unit 1, a power supply circuit 8, a driver circuit 9 that processes a digital video signal and applies it to a drive segment of the liquid crystal panel 4, and a backlight drive circuit 10 are mounted on a common circuit board 7. Since it does not protrude from the liquid crystal panel 4 in a plan view, it can be completed as a small unit.
[0034]
And since the backlight drive circuit 10 mounted on the same circuit board 7 is doubly covered and electromagnetically shielded by the first shield case 11 and the folded piece 3c, the backlight drive circuit 10 in the backlight drive circuit 10 It is possible to prevent radiation noise from the inverter circuit from affecting the digital video signal.
[0035]
In addition, since the entire circuit board 7 is covered with the second shield case 3, the noise emitted from the outside of the display unit 1 is shielded and adversely affects the digital signal processing in the driver circuit 9. Can be prevented.
[0036]
Here, the opening 3 </ b> A formed in the second shield case 3 is formed slightly larger than the ceiling surface 11 </ b> A of the first shield case 11. Thereby, when the 1st shield case 11 is covered with the 2nd shield case 3, the 1st shield case 11 can be reliably inserted in the said opening part 3A. Therefore, as illustrated in FIG. 4, a gap 20 is formed between the first shield case 11 and the opening 3 </ b> A of the second shield case 3.
[0037]
Here, the opening dimension of each gap 20 is the maximum linear length dimension L of this gap 20 (the dimension of the portion of the gap 20 that can take the longest linear distance). 1 is set so that noise from various electronic circuits existing outside of 1 does not affect the driver circuit 9.
[0038]
Since the driver circuit 9 processes a digital video signal, it is necessary to assume a circuit having a frequency up to about 1 GHz as an external electronic circuit that affects the driver circuit 9.
[0039]
Assuming that the processing frequency of the external noise generation circuit is f = 1 GHz and the velocity of electrons in space is v (v≈3.0 × 10 ⁸ ), the wavelength λ of the radiation noise is given by λ = v / f,
λ = v / f = 3.0 × 10 ⁸ /1.0×10 ⁹ = 0.3 m
[0040]
The further the linear distance of the gap 20 is from the wavelength of the radio wave emitted from an external noise source, the lower the possibility that the gap 20 receives the radio wave. Therefore, as described above, the noise of the external circuit is assumed up to 1 GHz, and the length dimension L of the gap 20 is set to be equal to or smaller than 1/12 of the wavelength emitted from the noise source. Reception up to the wave can be blocked.
[0041]
When obtaining the wavelength of the 12th harmonic,
λ / 12 = 0.3 / 12 = 0.025 m = 25 mm
[0042]
Therefore, by setting the length L of the gap 20 to 25 mm or less (L ≦ 25 mm), the influence of noise from the external circuit to the driver circuit 9 can be effectively prevented.
[0043]
In the above embodiment, the display unit 1 has been described as an example of the electronic device. However, the present invention is not limited to this and may be other electronic devices.
[0044]
Moreover, although the backlight drive circuit 10 was illustrated and demonstrated as a noise generation source which a 1st shield case shields, you may cover other noise generation sources (for example, power supply circuits etc.).
[0045]
Further, in the present invention, the noise generation source is confined in the first shield case 11 and electromagnetically shielded (shielded) to prevent radiation noise from leaking outside. A component or an electronic circuit that is likely to malfunction when it is received may be provided in the first shield case 11.
[0046]
Moreover, an opening part may be formed in the side surface of the 2nd shield case 3, and the side surface of the 1st shield case 11 may appear in the said opening part.
[0047]
【The invention's effect】
As described above, in the present invention, since the overlap between the first shield case and the second shield case can be avoided, the electronic device can be made thin.
[0048]
In addition, it is possible to shield the noise generation source and shield other circuits in the device, and to make the other circuits less susceptible to radiation noise from the noise generation source.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a display unit as an embodiment of an electronic apparatus of the invention,
FIG. 2 is an exploded perspective view of a display unit,
3 is a cross-sectional view of the display unit taken along line III-III in FIG.
4 is a plan view showing the relationship between the opening and the first shield case as seen from the direction of arrow IV in FIG. 2;
[Explanation of symbols]
1 Display unit (electronic equipment)
2 Front frame 3 Second shield case 3A Openings 3a, 3b Inclined side surface 3c Folded piece 4 Liquid crystal panel 5 Fluorescent lamp 6 Light guide member 7 Circuit board 9 Driver circuit 10 Backlight drive circuit (noise generation source)
11 First shield case 11b Elastic piece 20 Gap L Gap length

Claims (5)

A circuit board having electronic components mounted, the first and the shield case, before Symbol electronic components on the circuit board which is not covered with the first shield case covering a part of the electronic components mounted on the circuit board In an electronic device provided with a second shield case covering
The first shield case and the second shield case both have a ceiling surface facing the circuit board and a side surface perpendicular to the ceiling surface, and the side surface rises from the circuit board,
The second shield case is provided with an opening that opens to the ceiling surface, and a plurality of folded pieces that are bent from the ceiling surface toward the circuit board with an edge of the opening as a fold. The first shield case enters the opening and is surrounded by the plurality of folded pieces, and the surface of the ceiling surface of the first shield case is flush with the surface of the ceiling surface of the second shield case. Position to,
Either one of the side surface of the first shield case and the folded piece is provided with an elastic piece, and the elastic piece is pressed against the other, and the first shield case and the second shield case are electrically connected. An electronic device characterized by that. In the first shield case, an inclined side surface is formed between the ceiling surface and the side surface, and in the second shield case, an inclined side surface is formed between the ceiling surface and the side surface, The inclined side surface of the first shield case is covered with the inclined side surface of the second shield case, an elastic piece is formed on one of the both inclined side surfaces, and the elastic piece is elastically pressed to the other inclined side surface. and it has claim 1 electronic device according. The electron according to claim 1 or 2 , wherein one or more gaps are provided between the first shield case and the second shield case, and the longest linear distance of the gap is 25 mm or less. machine. The circuit board includes a circuit as a noise source, a digital circuit is implemented, any of the to noise sources become circuits claims 1 covered with the first shield case 3 1 The electronic device as described in the paragraph . 5. The electronic apparatus according to claim 4, wherein the noise source circuit is a backlight drive circuit of a display device, and the digital circuit is a digital video signal processing circuit for driving the display device.

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