JPH0998534A - Overcurrent protective structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the firing of a resistor and the spreading fire around the resistor using a simple and low-cost structure by preventing the firing of the resistor by a method wherein a fuse section blows even if overcurrent runs in the resistor. SOLUTION: A resistor 22, a capacitor 25, and a Zener diode 24 are mounted on a printed wiring board 20 to form a power input section of a proximity switch. A part of a wiring pattern 40 which constitutes the power input section that is serial with the resistor is passed under the resistor 22 to form a fuse section 47. When a power supply is reversely connected to the proximity switch under no load and thereby overcurrent runs in the resistor 22, the resistor 22 generates heat and fuses the fuse section 47 of the wiring pattern 40 and then the power input section is disconnected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection structure for protecting electronic parts, equipment and the like from ignition and burning due to overcurrent. For example, the present invention relates to an overcurrent protection structure suitable for use in a proximity switch or a photoelectric switch that detects a metal body.

[0002]

2. Description of the Related Art A high-frequency oscillation type proximity sensor is generally used as a sensor for magnetically detecting the presence of a metal body in a non-contact manner. Among such proximity sensors, a proximity switch is known in which a detection coil detects and outputs an electric signal each time a metal body such as a pachinko ball passes.

In such a proximity switch 71,
As shown in FIG. 10, the power supply input section on the printed circuit board has a resistor 22 and a capacitor 2 which form a noise removing circuit.
5, the Zener diode 24 is mounted. Between the power supply connection terminals 72 and 73 of the power supply input section, normally 12 to 24
A V power supply 74 is connected, and the power supply side includes the internal resistance of the power supply 74 and the load resistance 75.

However, when an incorrect power source 74 is connected between the power source connecting terminals 72 and 73 and an excessive voltage higher than the rated voltage is applied, an overcurrent flows in the proximity switch 71 as indicated by the arrow B in FIG. . Further, even when the power supply 74 is mistakenly attached in the positive and negative reverse directions with no load resistance, an overcurrent flows through the proximity switch 71 as indicated by the arrow B in FIG. In these cases, the resistor 22 provided in the power input unit generates heat due to overcurrent, and the resistor 22 does not stop burning, but the proximity switch 71 fires and spreads to a device or the like incorporating the proximity switch 71. Cause

In order to prevent the spread of heat due to heat generation, if a resistor 22 having a small heat capacity is used, the resistor 22 is damaged in a short time due to heat generation due to overcurrent and is opened, so that the overcurrent can be immediately cut off. However, the resistor 22 with a small heat capacity
In some cases, the characteristics may be changed or destroyed due to the influence of static electricity, noise, etc., so that there is a problem that the performance of the entire circuit is deteriorated.

On the other hand, the method of using a glass tube fuse or a chip fuse is also widely used. However, these fuses require a large mounting area for arranging them on a substrate, which results in a high cost. However, there is a problem that it is not suitable for a proximity switch or the like that is small in size and low in unit price.

As shown in FIG. 11, a pattern fuse 76 formed by meandering a narrow pattern 77 on a substrate is also known, but there is a problem that a stable operation cannot be obtained due to variations in manufacturing the substrate. It was Further, the pattern fuse 76 with stable operation could be manufactured only by a high cost method.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the drawbacks of the above conventional examples, and an object of the present invention is to separately provide a fuse or the like in a circuit including a resistor, particularly in a power input section. An object of the present invention is to provide an overcurrent protection structure that can prevent the risk of fire spread and fire due to overcurrent at low cost by using a resistor having a large heat capacity without using any parts.

[0009]

An overcurrent protection structure according to a first aspect of the present invention is an overcurrent flowing through a power input unit including a wiring pattern formed on a substrate and a resistor mounted on the substrate. Is a protection structure against an overcurrent that cuts off the wiring pattern, and is characterized in that a part of the wiring pattern is arranged in the vicinity of the resistor so that the wiring pattern is melted by the heat when the overcurrent flows to the resistor.

An overcurrent protection structure according to a second aspect of the present invention is an overcurrent protection structure for interrupting an overcurrent flowing through a circuit portion formed on a substrate, wherein the overcurrent of the circuit portion is It is characterized in that a resistor is inserted in a position where the current flows and a part of the wiring pattern of the circuit portion is arranged in the vicinity of the resistor so that the wiring pattern is melted by heat when an overcurrent flows through the resistor.

[0011]

According to the overcurrent protection structure of the present invention, when an overcurrent flows through the power supply input portion (in the case of claim 1) and the other circuit portion (in the case of claim 2), the resistance heats up due to the overcurrent. Then, the wiring pattern near the resistor is melted. As a result, it is possible to prevent the overcurrent from being interrupted, the resistance or the like to be ignited, and the electronic component or device provided with the overcurrent protection structure, the surrounding equipment, or the like from being spread or burned.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

(Overall Configuration of Penetration Type Proximity Sensor) One embodiment of the present invention will be described by taking a penetration type proximity switch A for detecting penetration of a pachinko ball or the like as an example. FIG. 1 is an exploded perspective view of the proximity switch A. As shown in the figure, the proximity switch A includes a coil portion 13, an electronic circuit portion 19, and a pair of shield rings 31 and 32 in a flat rectangular parallelepiped casing including an upper case 1 and a lower case 2.

The upper and lower cases 1 and 2 constituting this casing are formed with substantially circular through holes 3 and 4 facing each other. A ring-shaped projecting edge 9 is provided around the through hole 4 of the lower case 2 toward the inner surface side of the lower case 2, and the lower shield ring is positioned at a part of the projecting edge 9. A boss 10 for protruding is provided. A pin 11 is provided upright in the vicinity of the through hole 4 on the inner surface of the lower case 2. Further, the left and right side walls of the lower case 2 facing the pins 11 are provided with recesses 12 for holding projections 30 of the electronic circuit section 19 described later. A ring-shaped projecting edge (not shown) is also provided around the through hole 3 of the upper case 1 as in the lower case 2, and the upper shield ring 31 is provided at a part of the projecting edge. A boss (not shown) for positioning is projected.

Further, elastic pieces 6 and 7 having engaging claws 5 are respectively hung at two points and both side surfaces of the corner portion of the upper case 1, and the lower case 2 corresponds to the respective engaging claws 5. A protrusion 8 (the protrusion of the corner portion is not shown) is provided so as to cover the lower case 2 with the upper case 1 so that the engaging claws 5 are engaged with the protrusion 8. The housing can be configured by combining 1 and 2.

The coil portion 13 is formed by winding a coil winding 15 on a resin coil spool 14. The coil spool 14 has a through hole 17 for allowing a metal body (that is, a pachinko ball) to pass through inside a winding drum portion 16 for winding the coil winding 15, and The board connecting portion 18 projects from the end portion. Coil spool 1
The front end portion of the electronic circuit portion 19 is connected and integrated with the board connecting portion 18 of No. 4.

The electronic circuit section 19 includes a printed wiring board 20.
Wiring pattern (copper foil pattern) 40 formed on the upper surface of the
IC21, resistors 22 and 23, Zener diode 2 on top
4, components such as capacitors 25, 26 and 27 are mounted to form an oscillation circuit, a detection circuit, an output circuit and the like.
On the lower surface of the printed wiring board 20, as shown in FIG.
A copper foil 28 for electrostatic shielding is stuck on almost the entire surface. Printed wiring board 20 inserted in board connecting portion 18
The pin 11 of the lower case 2 is attached to the tip of the board and the board connecting portion 18.
A pin insertion hole 29 is formed at a position corresponding to. In addition, the protrusions 30 are provided on both sides of the front end of the printed wiring board 20.
Are provided, and both ends of the coil winding 15 of the coil portion 13 are soldered to the electronic circuit portion 19 by the protrusions 30.

The shield rings 31 and 32 are metal ring-shaped members formed of, for example, a copper foil plate, and by combining these to cover the outer peripheral portion of the coil portion 13, the magnetic flux of the coil portion 13 becomes the outer periphery. It prevents leakage to the parts and prevents malfunction due to surrounding metal. The shield rings 31 and 32 are provided with a thin notch 33 so as not to touch the coil winding 15 and the like.
A projecting piece 34 is erected at 3. Further, the inner circumferences of the shield rings 31 and 32 are formed to have substantially the same dimensions as the outer circumferences of the projecting edges 9 of the upper and lower cases 1 and 2, and a notch recess 35 is provided in a part of the inner circumferences.

When assembling the proximity sensor A, however, the lower shield ring 3 is provided around the projecting edge 9 of the lower case 2.
2 is positioned, the shield ring 32 is positioned by the projecting edge 9 and the cutout recess 3 of the shield ring 32 is positioned.
5 is fitted into the boss 10 of the lower case 2 and is prevented from rotating.
Then, the coil portion 13 and the electronic circuit portion 19 are housed in the lower case 2 by press-fitting the pins 11 of the lower case 2 into the board connection portions 18 of the coil portion 13 and the pin insertion holes 29 of the printed wiring board 20. The protrusion 30 of the printed wiring board 20 is housed in the recess 12 of the lower case 2 and positioned and held. When the upper case 1 is put on the coil part 13 after the upper shield ring 31 is put on the coil part 13, the projecting edge of the upper case 1 is fitted into the inner circumference of the upper shield ring 31 to position the shield ring 31. Then, the cutout concave portion 35 of the upper shield ring 31 is fitted into the boss of the upper case 1 to prevent the shield ring 31 from rotating. Further, when the upper case 1 is pressed against the lower case 2, the engaging claws 5 provided on the elastic pieces 6 and 7 of the upper case 1 are engaged with the protrusions 8 of the lower case 2, and the upper and lower cases 1 and 2 are integrated. The housing is configured by forming the coil portion 13 and the electronic circuit portion 19 into the housing. In the proximity sensor A thus assembled, the through holes 3, 17 and 4 of the upper case 1, the coil spool 14 and the lower case 2 are integrated to form a through portion through which a metal body passes.

When the upper and lower shield rings 31 and 32, the coil portion 13 and the electronic circuit portion 19 are housed in the upper and lower cases 1 and 2, the protruding piece 34 projecting from the lower shield ring 32 becomes a printed wiring board. The lower shield ring 32 is grounded by being pressed against the copper foil 28 on the lower surface of 20. further,
When the upper shield ring 31 contacts the lower shield ring 32, the upper shield ring 31 is also grounded. As a result, the outer peripheral portion of the coil portion 13 is covered by the grounded upper and lower shield rings 31 and 32, and the magnetic flux from the coil portion 13 is prevented from leaking to the outer peripheral portion and malfunctioning.

(Structure of Electronic Circuit Section) FIG. 2 is a circuit diagram showing the circuit structure of a direct current two-wire type through-type proximity switch A, and FIG. 3 is a functional block diagram of the circuit. The coil unit 13 (coil winding 15) and the capacitor 27 connected in parallel form an LC oscillation circuit 36. Reference numeral 21 is a custom IC for a through-type proximity switch, which includes LC and RV
Is an oscillation signal terminal, RE is a terminal for connecting an adjusting resistor 23 for adjusting a feedback current, and INT is a terminal for connecting an integrating capacitor 26. Then IC
The detection circuit 37 and the output circuit 38 are configured by the 21, the adjustment resistor 23, and the integrating capacitor 26. In addition, the power supply passes through the noise removing circuit 39 composed of the resistor 22, the capacitor 25, and the Zener diode 24, and the power supply terminal V _CC and the ground terminal GND of the IC 21
It is connected to the.

The oscillator circuit 36 oscillates at a constant frequency, and its output is transmitted to the detector circuit 37. When the metal body approaches the coil portion 13, the conductance of the coil portion 13 increases, the oscillation condition of the oscillation circuit 36 changes, the amplitude decreases, or the oscillation level becomes a predetermined threshold value or less. The proximity sensor A detects the approach or passage of the metal body due to the decrease in the amplitude or the oscillation level, and the output circuit 38
An object detection signal is output via. The detection circuit 37 and the output circuit 38 configure a signal processing unit that detects the proximity of the metal body based on the change in the oscillation state. Further, the noise removing circuit 39 removes noise that gets on the power supply voltage and enters the IC 21.

4 and 5 show the printed wiring board 20.
FIG. 6 is a diagram showing the wiring pattern 40 on the front surface side and the back surface side and the pattern of the copper foil 28 for shielding. In FIGS. 4 and 5, the shaded area is the area on the high potential side, and the satin area is the area on the ground potential. Ground potential pads 41 and 42 provided on the front and back of the protrusion 30.
Are electrically connected to each other by winding the coil winding 15 around the protrusion 30 and soldering. 43,44
Is an electrode pad and a dummy pad on the high potential side for soldering the coil winding 15. Further, 45 and 46 are power supply connection pads on the high potential side and the ground side. In the wiring pattern 40 on the front surface side, the IC 21 is mounted at the position shown by the chain double-dashed line in FIG. 4, and the resistors 22, 23, capacitors 25, 26, 27, and zener diode 24 are mounted as shown by the symbols in FIG. Has been done. Here, a part of the wiring pattern 40 in the power input part (a part in series with the resistor 22) is soldered to the wiring pattern 40 and mounted on the printed wiring board 20 as shown in FIG. The fuse portion 47 is wired so as to pass through the lower surface of the (carbon film resistance) 22. The width of the fuse portion 47 has a narrow line width (for example, a line width of about 0.2 mm) so that it is easily blown by the heat of the resistor 22.

When the power supply is erroneously connected between the power supply connection pads 45 and 46 of the feedthrough type proximity switch A in the state of no load or light load in the positive and negative reverse directions, the wiring pattern 40 is shown in FIG. Overcurrent flows as indicated by the arrow. Due to this overcurrent, the resistance 22 of the power supply input section generates heat. When the resistor 22 generates heat, the fuse portion 47 thereunder is blown. When the fuse part 47 is blown, the power input part is disconnected and opened, so that no current flows through the resistor 22 and
Can be prevented from catching fire. Therefore, it is possible to prevent the proximity switch A from catching fire and causing a pachinko machine or the like incorporating the proximity switch A to spread or burn.

Similarly, even when a power source with an excessive voltage higher than the rated value is connected, the fuse portion 47 is blown by the heat generated by the resistor 22, so that ignition from the resistor 22 can be prevented. It is preferable that the fuse portion 47 passes through a position where the resistor 22 is most likely to generate heat, for example, the lower surface of the central portion of the resistor 22.

(Results of actual measurement) A carbon film resistor of 100Ω was used as the resistor 22 of the power input unit, the width of the fuse portion 47 wired on the lower surface of the resistor 22 was set to 0.2 mm (design value), and a 24 V DC power source was used. The time from the turning on of the power source to the disconnection of the fuse portion 47 was measured by connecting in positive and negative directions. Table 1 shows the conditions of the power supply capacity and the time until the fuse unit 47 is disconnected and the power supply input unit is disconnected for the 17 samples.

[0026]

[Table 1]

In each of the sample Nos. 1 to 10, since a current of 240 mA initially flows through the resistor 22, several seconds to 1
The power input section is disconnected in a few seconds. On the other hand, in Sample Nos. 11 to 17, since the power source capacity is small, a current smaller than 240 mA can flow through the resistor 22, so that it takes a long time to disconnect the power source input section.
It has ignited. However, sample Nos. 11-17
Even under the condition of the power supply capacity as described above, by changing the value of the resistor 22 or the line width of the fuse portion 47, it is possible to disconnect the circuit in the same time as the sample Nos. 1 to 10.

FIG. 8 shows another embodiment of the present invention, which is a case of a proximity switch B of a DC 3-wire type. In this proximity switch B, the power input terminal 48
And a DC power supply connected between the ground terminal 49 and the resistor 2
After the noise is removed by the power supply input section composed of 2 and the Zener diode 24, it passes through the diode 50 and the resistor 51, is converted into a constant voltage by the constant voltage circuit 52, and is supplied to the sensor circuit 53 to oscillate the coil section 13. . The constant voltage circuit 52 includes an NPN transistor 54, a resistor 55, a capacitor 59, and a zener diode 56. When the metal body is not detected, the detection signal output terminal 57 is H (high), but when the coil unit 13 detects the passage of the metal body, the sensor circuit 53 turns on the output transistor 58. Detection signal output terminal 5
7 outputs an L (low) signal.

Also in such a DC 3-wire proximity switch B, a part of the wiring pattern of the power supply input section is provided with a resistor 22.
The fuse portion 47 is formed by wiring so as to pass through the lower surface of the resistor 22. If an overcurrent flows through the resistor 22,
It is possible to prevent the ignition of the resistor 22 by melting the fuse portion 47 of the wiring pattern and disconnecting the power supply input portion due to the heat generation of 2.

Further, FIG. 9 shows another embodiment of the present invention, showing an AC two-wire type proximity switch C. In this proximity switch C, the AC power source 6
The AC current supplied from 0 is full-wave rectified by the rectifying bridge circuit 61, converted into a constant voltage by the constant voltage circuit 62, and supplied to the sensor circuit 53 to oscillate the coil unit 13. The constant voltage circuit 52 is composed of the NPN transistor 6
3, a resistor 64 and a Zener diode 65. When the coil unit 13 detects the passage of the metal body, the sensor circuit 53 turns on the thyristor 66 and turns on the relay 67.

Also in such an AC two-wire proximity switch C, a resistor 22 is added to the power input section, and wiring is performed so that a part of the wiring pattern of the power input section passes through the lower surface of the resistor 22 and the fuse is connected. By forming the portion 47, when an overcurrent flows, the fuse portion 47 of the wiring pattern is melted by the heat generated by the resistor 22 to disconnect the power supply input portion and protect the circuit from the overcurrent.

In each of the above embodiments, the case of overcurrent protection in the power supply input section has been described. However, as is apparent from the configuration and the effect of the present invention, the present invention can be applied to the circuit section other than the power supply input section. It goes without saying that it can be implemented.

[0033]

According to the present invention, when an overcurrent flows through a power supply input section and other circuit parts, the resistance heats up due to the overcurrent, the wiring pattern near the resistance is melted, and the overcurrent is cut off.

Therefore, it is possible to prevent the resistance from being ignited and spread to the electronic parts and devices in which the resistance is incorporated, the peripheral equipment, or the like. In addition, even if a resistor having a large heat capacity is used, it is possible to prevent the surrounding equipment from burning and spreading, and the circuit performance is not deteriorated. Further, since no glass tube fuse or chip fuse is used, it is not necessary to increase the substrate area. Furthermore, since the wiring pattern can be formed at the same time as other wiring patterns, there is an advantage that no extra cost is required for overcurrent protection.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a penetration type proximity switch according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a circuit configuration of the through-type proximity switch of the above.

FIG. 3 is a functional block diagram of the above circuit.

FIG. 4 is an enlarged view showing a wiring pattern on the front surface side of the above-mentioned printed wiring board.

FIG. 5 is a view showing a pattern of a copper foil on the back surface side of the above printed wiring board.

FIG. 6 is a partially cutaway enlarged cross-sectional view showing a relationship between a resistance and a wiring pattern on the same printed wiring board.

FIG. 7 is an explanatory diagram of an operation of the above.

FIG. 8 is a circuit diagram showing another embodiment of the present invention.

FIG. 9 is a circuit diagram showing still another embodiment of the present invention.

FIG. 10 is a partially omitted circuit diagram for explaining a problem of a conventional proximity switch.

FIG. 11 is a diagram showing a conventional pattern fuse.

[Explanation of symbols]

 19 Electronic Circuit Section 20 Printed Wiring Board 22 Resistance 24 Zener Diode 25 Capacitor 40 Wiring Pattern 47 Fuse Section

Claims (2)

[Claims] 1. An overcurrent protection structure for interrupting an overcurrent flowing through a power supply input section including a wiring pattern formed on a substrate and a resistor mounted on the substrate, wherein a part of the wiring pattern is provided. Is arranged in the vicinity of the resistor so that the resistor is melted by heat when an overcurrent flows through the resistor. 2. A protection structure at the time of overcurrent for interrupting an overcurrent flowing through a circuit portion formed on a substrate, wherein a resistor is inserted at a position where the overcurrent of the circuit portion flows, and wiring of the circuit portion is provided. The overcurrent protection structure, wherein a part of the pattern is arranged in the vicinity of the resistor so that the pattern is melted by heat when an overcurrent flows through the resistor.