JP4457481B2 - Magnetic detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic detector, and more particularly to a magnetic detector used for detecting a steel ball such as a pachinko ball using a semiconductor magnetoresistive element, for example.
[0002]
[Prior art]
FIG. 12 is a circuit diagram showing an example of a conventional magnetic detector. The magnetic substance detector 1 includes an amplifying transistor 2. A semiconductor magnetoresistive element 3 is connected between the base and emitter of the amplifying transistor 2. A constant current circuit 4 and a chattering preventing resistor 5 are connected between the base and collector of the amplifying transistor 2. The constant current circuit 4 includes an FET 6 and a resistor 7. One end of the resistor 7 is connected to the source of the FET 6, and the other end of the resistor 7 is connected to the gate of the FET 6. Further, the other end of the resistor 7 is connected to the resistor 5. The collector of the amplifying transistor 2 and the drain of the FET 6 are connected to the power supply voltage Vin. Further, the emitter of the amplifying transistor 2 is connected to the output resistor 8.
[0003]
In the magnetic detector 1, a bias magnetic field is applied to the semiconductor magnetoresistive element 3 by a magnet or the like. When the magnetic body approaches the semiconductor magnetoresistive element 3, the magnetic field concentrates on the semiconductor magnetoresistive element 3 between the magnet and the magnetic body, and the resistance value increases. Therefore, the voltage applied between the base and the emitter of the amplifying transistor 2 increases, and the current flowing from the amplifying transistor 2 to the output resistor 9 increases, so that a high output voltage is obtained. Thus, the magnetic substance can be detected by measuring the output voltage from the resistor 9.
[0004]
In the magnetic detector 1, since the constant current circuit 4 is connected, a constant current can be obtained even if the power supply voltage Vin varies. Therefore, it can be set as the magnetic body detector which is hard to be influenced by the fluctuation | variation of a power supply voltage. In such a magnetic detector 1, by using a resistor having a resistance temperature characteristic corresponding to the resistance temperature characteristic of the semiconductor magnetoresistive element 3 as the resistor 7 connected to the FET 6, the operating voltage of the amplifying transistor 2 is increased. The voltage applied between the base and the emitter can be adjusted in accordance with the temperature characteristics. By doing in this way, the magnetic body detector which can detect a magnetic body in a wide temperature range can be obtained.
[0005]
[Problems to be solved by the invention]
However, in such a magnetic substance detector, the semiconductor magnetoresistive element for detecting the magnetic substance reacts even with an external magnetic field. That is, when an external magnetic field is applied to the semiconductor magnetoresistive element, the resistance value changes, and the magnetic detector malfunctions. For example, when a pachinko ball is detected using a magnetic body detector on a pachinko machine or the like, as shown in FIG. 13, the magnetic body detector is installed at a location where the pachinko ball is desired to be detected. However, when a magnetic field is applied to the magnetic detector by a magnet or the like from the outside of the glass, the same output as when the pachinko ball has passed is measured even though the pachinko ball has not passed.
[0006]
Therefore, a main object of the present invention is to provide a magnetic detector capable of preventing malfunction due to an external magnetic field.
[0007]
[Means for Solving the Problems]
The present invention includes a first resistor block including at least one semiconductor magnetoresistive element, a FET, and a second resistor block including at least one semiconductor magnetoresistive element connected between a gate and a source of the FET. And a first resistor block connected between the base and the emitter, and a constant current circuit connected between the base and the collector, the first resistor A magnetic substance detector in which one of the block or the second resistance block reacts more strongly with the magnetic body than the other, and the first resistance block and the second resistance block react to the same extent with respect to an external magnetic field. .
Such a magnetic detector includes means for applying a bias magnetic field to at least one of the semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block.
The semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block can be formed of the same material.
Furthermore, the semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block can be formed on the same substrate.
The semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block may be formed of different materials.
[0008]
By including the semiconductor magnetoresistive element in the first resistor block and the second resistor block, the resistance value of the semiconductor magnetoresistive element changes when the magnetic body approaches or an external magnetic field is applied. At this time, one of the first resistance block and the second resistance block reacts more strongly than the other due to the magnetic material, whereby the voltage applied between the base and the emitter of the amplifying transistor changes, and the amplifying transistor The output changes. However, since the first resistance block and the second resistance block react to the same extent with respect to the external magnetic field, a change in the voltage applied between the base and the emitter of the amplifying transistor can be suppressed, and the amplifying transistor The output from is almost unchanged.
In such a magnetic substance detector, when a bias magnetic field is applied to one of the first resistance block or the second resistance block, the semiconductor magnetoresistive element to which the bias magnetic field is applied is separated by the magnetic substance. The strength of the magnetic field applied to the element changes, and the magnetic field strength of the semiconductor magnetoresistive element to which no bias magnetic field is applied is hardly changed depending on the magnetic material. However, depending on the external magnetic field, the strength of the magnetic field applied to both semiconductor magnetoresistive elements changes to the same extent.
Further, when a bias magnetic field is applied to both of the semiconductor magnetoresistive elements, by placing one semiconductor magnetoresistive element in the vicinity of the passage of the magnetic material, the magnetic material has a stronger magnetic field than the other semiconductor magnetoresistive element. The height can be changed greatly.
The two semiconductor magnetoresistive elements may be formed of the same material or different materials.
When two semiconductor magnetoresistive elements are formed of the same material, they can be formed on the same substrate.
[0009]
The above object, other objects, features, and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the drawings.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram showing an example of the magnetic detector of the present invention. The magnetic material detector 10 includes, for example, an NPN amplification transistor 12. A first resistor block 14 is connected between the base and emitter of the amplifying transistor 12. A series circuit of a constant current circuit 16 and a chattering preventing resistor 18 is connected between the collector and base of the amplifying transistor 12. The constant current circuit 16 includes an FET 20 and a second resistance block 22. One end of the second resistor block 22 is connected to the source of the FET 20, and the other end of the second resistor block 22 is connected to the gate of the FET 20. Further, the other end of the second resistor block 22 is connected to the chattering preventing resistor 18. The collector of the amplifying transistor 12 and the drain of the FET 20 are connected to the power supply voltage Vin. The emitter of the amplifying transistor 12 is connected to the first resistor block 14 and grounded via the output resistor 24.
[0011]
Each of the first resistance block 14 and the second resistance block 22 includes at least one semiconductor magnetoresistive element. As these semiconductor magnetoresistive elements, for example, those formed of the same material are used. The first resistor block 14 and the second resistor block 22 may be configured only by a semiconductor magnetoresistive element or may be configured in combination with other resistors. A bias magnetic field is applied to the first resistance block 14 and the second resistance block 22 by, for example, a magnet.
[0012]
This magnetic detector 10 is used as a steel ball detector such as a pachinko ball, for example. As shown in FIG. 2, the steel ball detection device 30 includes a substrate 34 in which a through hole 32 is formed, and a case portion 36 is formed adjacent to the through hole 32. In the case portion 36, the first resistance block 14 is disposed at a portion facing the through hole 32. Further, a magnet 38 is disposed so as to be in contact with the first resistance block 14, and a DC magnetic field is applied to the semiconductor magnetoresistive element in the first resistance block 14. Therefore, when the steel ball 40 passes through the through hole 32, the magnetic field concentrates in the first resistance block 14 portion, and the resistance value of the semiconductor magnetoresistive element changes.
[0013]
In this magnetic substance detector 10, the constant current circuit 16 can obtain a constant current even if the power supply voltage Vin varies. That is, when the power supply voltage Vin increases, the current flowing through the second resistance block 22 increases, and the voltage input to the gate of the FET 20 increases. For this reason, the resistance value between the drain and source of the FET 20 is increased, and the current flowing therethrough is suppressed. Conversely, when the power supply voltage Vin decreases, the resistance value between the drain and source of the FET 20 decreases and the current flowing therethrough increases. In this way, a constant current is supplied from the constant current circuit 16 regardless of the fluctuation of the power supply voltage Vin. Therefore, a constant voltage is applied between the base and emitter of the amplifying transistor 12 regardless of the fluctuation of the power supply voltage. If the gate of the FET 20 and the base of the amplifying transistor 12 are short-circuited, the switching operation of the amplifying transistor 12 becomes too fast, and the output voltage also chatters according to the chattering of the resistance value of the first resistor block 14. Will be caused. Therefore, the switching operation of the amplifying transistor 12 is delayed by using the chattering preventing resistor 18. Further, since the semiconductor magnetoresistive elements used for the first resistor block 14 and the second resistor block 22 are formed of the same material, they have the same resistance temperature characteristics and are less affected by temperature changes. Can operate over a wide temperature range.
[0014]
FIG. 3 shows a case where a magnetic substance as a detection object is detected with respect to the gap characteristic of sensitivity of the semiconductor magnetoresistive element in such a magnetic substance detector 10, and FIG. 4 shows a case where a magnet having a strong magnetic force is detected. Shown in From these characteristics, it can be seen that the sensitivity of the semiconductor magnetoresistive element shows a larger value when detecting a magnet having a strong magnetic force than when detecting a magnetic body. It can also be seen that the magnitude of sensitivity decreases as the gap increases.
[0015]
In this magnetic material detector 10, the first resistance block 14 reacts strongly with the magnetic material, and the first resistance block 14 and the second resistance block 22 respond to the external magnetic field to the same extent. Formed. For example, in the case of the steel ball detection device 30, as shown in FIG. 5, the first resistance block 14 is disposed at a position where the steel ball 40 is detected, and the second resistance block 22 is separated from the first resistance block 14. It is arranged at a slightly separated position.
[0016]
In such a steel ball detection device 30, when the steel ball 40 passes through the vicinity of the first resistance block 14, the bias magnetic field concentrates on the first resistance block 14, and the semiconductor included in the first resistance block 14. The resistance value of the magnetoresistive element 26 is increased. Therefore, the resistance value of the first resistor block 14 is increased, and the voltage applied between the base and the emitter of the amplifying transistor 12 is increased. As shown by the solid line in FIG. The current flowing through the resistor 24 increases. Therefore, the output voltage obtained from the resistor 24 is increased, and the passage of the steel ball 40 can be detected.
[0017]
When a magnet approaches from the outside, a magnetic field generated by the magnet is applied to both the first resistor block 14 and the second resistor block 22, and the semiconductor magnetoresistive elements 26 and 28 included in these resistor blocks 14 and 22. The resistance value increases simultaneously. The relationship between the resistance value and the current value of the constant current circuit 16 using the FET 20 is such that the current value decreases as the resistance value increases as shown in FIG. Therefore, the change in the base potential of the amplifying transistor 12 obtained by the product of the current value and the resistance value of the first resistor block 14 is reduced, and malfunction of the amplifying transistor 12 can be prevented.
[0018]
FIG. 8 is a diagram showing an output voltage when a magnet approaches the conventional magnetic detector and the magnetic detector 10 of the present invention. In FIG. 8, two dotted lines indicate the output voltage during standby when the magnet is not approaching for the conventional magnetic detector and the magnetic detector of the present invention, respectively. From FIG. 8, it can be seen that in the conventional magnetic substance detector, the output voltage is increased by bringing the magnet closer from the outside, but in the magnetic substance detector 10 of the present invention, the output voltage hardly changes. Thus, in the magnetic substance detector 10 of the present invention, the magnetic substance is detected, but the output does not change depending on the external magnetic field.
[0019]
The first resistor block 14 and the second resistor block 22 may be arranged adjacent to each other as shown in FIG. In this case, the semiconductor magnetoresistive element 26 of the first resistance block 14 is arranged at the detection position of the steel ball 40 and arranged so that the bias magnetic field is likely to concentrate on the first resistance block 14 when the steel ball 40 passes. Is done. Here, the magnetosensitive surface of the semiconductor magnetoresistive element included in the first resistor block 14 and the magnetosensitive surface of the reaction body magnetoresistive element 28 included in the second resistor block 22 are arranged in opposite directions.
[0020]
The semiconductor magnetoresistive elements 26 and 28 included in the first resistor block 14 and the second resistor block 22 may be formed on the same chip. In this case, as shown in FIG. 10, the semiconductor magnetoresistive element 26 included in the first resistance block 14 is disposed in the detection unit of the steel ball 40. Here, the magnetosensitive surface of the semiconductor magnetoresistive element 26 included in the first resistor block 14 and the magnetosensitive surface of the semiconductor magnetoresistive element 28 included in the second resistor block 22 are arranged in the same direction. Even in such a case, the semiconductor magnetoresistive element 26 included in the first resistance block 14 only needs to be disposed in the detection portion of the steel ball 40. Furthermore, as shown in FIG. 11, reaction body magnetoresistive elements 26 and 28 included in the first resistor block 14 and the second resistor block 22 may be formed on the front and back of the same substrate. In this case, the magnetosensitive surface of the semiconductor magnetoresistive element 26 included in the first resistance block 14 is disposed on the steel ball 40 detection side.
[0021]
In such a magnetic substance detector 10, a bias magnetic field may be applied only to the first resistance block 14. In this case, when the steel ball 40 passes in the vicinity of the first resistance block 14, the bias magnetic field concentrates on the first resistance block 14, and the resistance value of the semiconductor magnetoresistive element 26 included in the first resistance block 14. Increases to increase the output voltage. However, even if the steel ball 40 passes in the vicinity of the second resistance block 22, the resistance value of the semiconductor magnetoresistive element 28 included in the second resistance block 22 does not change, and the output voltage does not change. When an external magnetic field is applied, the resistance values of the semiconductor magnetoresistive elements 26 and 28 included in the first resistor block 14 and the second resistor block 22 both increase, and the output voltage does not change.
[0022]
Further, in the arrangement of the magnetic detector 10 shown in FIGS. 5 and 9 to 11, the positional relationship of the semiconductor magnetoresistive elements 26 and 28 in each figure is reversed, and the semiconductor magnets included in the second resistor block 22 are reversed. The resistance element 28 may be disposed in the detection part of the steel ball 40. Here, a bias magnetic field is applied to both the first resistance block 14 and the second resistance block 22. In such a magnetic substance detector 10, when the steel ball 40 approaches the second resistance block 22, the resistance value of the semiconductor magnetoresistive element 28 included in the second resistance block 22 increases. Therefore, the current value of the constant current circuit 16 is reduced, the base potential of the amplifying transistor 12 indicated by the product of the resistance value and the current value of the first resistor block 14 is reduced, and the output transistor 12 The current flowing through the resistor 24 is reduced. Therefore, the output voltage obtained from the resistor 24 is reduced, and a waveform is obtained such that the output voltage is reduced when the steel ball 40 is detected as shown by the dotted line in FIG.
[0023]
Of course, also in such a magnetic substance detector 10, by arranging both the first resistance block 14 and the second resistance block 22 to respond to the external magnetic field to the same extent, the influence of the external magnetic field is exerted. The output voltage can be changed only in response to the magnetic material.
[0024]
Further, in such a magnetic material detector 10, it is possible to detect only the magnetic material and not be affected by the external magnetic field by applying a bias magnetic field only to the second resistance block 22.
[0025]
The semiconductor magnetoresistive elements 26 and 28 used for the first resistor block 14 and the second resistor block 22 may be made of different materials. Even in such a case, by making one of the first resistor block 14 and the second resistor block 22 react strongly with the magnetic material, both react with the external magnetic field to the same extent. Thus, it is possible to obtain a magnetic material detector 10 that can detect a magnetic material and is not affected by an external magnetic field.
[0026]
In the magnetic substance detector 10 shown in FIG. 1, the example using the NPN type amplifying transistor 12 and the N-channel FET 20 has been described. However, the same applies even when the PNP type amplifying transistor and the P-channel FET are used. The effect of can be obtained.
[0027]
【The invention's effect】
According to the present invention, it is possible to obtain a magnetic body detector that can prevent malfunction due to an external magnetic field and that can detect a magnetic body.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of a magnetic detector of the present invention.
FIG. 2 is an illustrative view showing an example in which the magnetic substance detector shown in FIG. 1 is applied to a steel ball detector.
3 is a graph showing the relationship between the gap and sensitivity when detecting a magnetic substance in the magnetic substance detector shown in FIG. 1;
4 is a graph showing a relationship between a gap and sensitivity when a magnet is detected in the magnetic substance detector shown in FIG. 1. FIG.
FIG. 5 is an illustrative view showing one example of a positional relationship between two semiconductor magnetoresistive elements and a steel ball of the steel ball detection device.
FIG. 6 is a waveform diagram showing an output voltage of a magnetic substance detector.
FIG. 7 is a graph showing the relationship between the resistance used in the constant current circuit and the current of the constant current circuit.
FIG. 8 is a diagram showing an output voltage when a magnet approaches the magnetic substance detector of the present invention and a conventional magnetic substance detector.
FIG. 9 is an illustrative view showing another example of a positional relationship between two semiconductor magnetoresistive elements and a steel ball of the steel ball detection device.
FIG. 10 is an illustrative view showing still another example of a positional relationship between two semiconductor magnetoresistive elements and a steel ball of the steel ball detection device.
FIG. 11 is an illustrative view showing another example of a positional relationship between two semiconductor magnetoresistive elements and a steel ball of the steel ball detection device.
FIG. 12 is a circuit diagram showing an example of a conventional magnetic detector.
FIG. 13 is an illustrative view showing a state in which a magnetic substance detector is attached to a pachinko machine.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Magnetic substance detector 12 Amplifying transistor 16 Constant current circuit 18 Chattering prevention resistor 20 FET
22 Second resistor block 24 Output resistor 26 Semiconductor magnetoresistive element 28 used in the first resistor block Semiconductor magnetoresistive element 30 used in the second resistor block Steel ball detector 38 Magnet 40 Steel ball

Claims (5)

A first resistance block including at least one semiconductor magnetoresistive element;
A constant current circuit including a FET and a second resistor block including at least one semiconductor magnetoresistive element connected between the gate and source of the FET, and the first resistor block includes a base and an emitter And the constant current circuit includes an amplifying transistor connected between the base and the collector,
One of the first resistor block or the second resistor block reacts more strongly with the magnetic body than the other, and the first resistor block and the second resistor block react to the same extent with respect to an external magnetic field. A magnetic detector. The magnetic body detector according to claim 1, further comprising means for applying a bias magnetic field to at least one of the semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block. . 3. The magnetic detector according to claim 1, wherein the semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block are formed of the same material. The magnetic according to any one of claims 1 to 3, wherein the semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block are formed on the same substrate. Body detector. 3. The magnetic detector according to claim 1, wherein the semiconductor magnetoresistive element used for the first resistor block and the semiconductor magnetoresistive element used for the second resistor block are formed of different materials.

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