JP2850456B2 - High frequency oscillation type proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high-frequency oscillation type in which an oscillation circuit is configured using a detection coil as an oscillation coil, and a detection object is detected by a decrease in output of the oscillation circuit. The present invention relates to a proximity switch, and more particularly, to a high-frequency oscillation type proximity switch with improved response speed of object detection.

[Conventional technology]

As a general characteristic of the oscillation circuit of this type of high-frequency oscillation type proximity switch, the time from the separation of the object to the growth of the oscillation is extremely long compared to the time from the approach of the object until the oscillation decreases. It has been known. For this reason, in order to improve the response speed of object detection of the proximity switch, it is necessary to shorten the above-mentioned oscillation growth time, and various methods have been proposed as one of the methods. There is one disclosed in -145742.

The proximity switch described in the above-mentioned publication is provided with a Schmitt circuit for detecting a decrease in the output of the oscillation circuit, and when the oscillation output of the oscillation circuit is reduced by the Schmitt circuit,
The oscillation is continued by reducing the resistance value of the amplitude adjusting resistor of the oscillation circuit. In this conventional example,
Although the response speed of object detection can be improved to some extent, the resistance for amplitude adjustment cannot be made too small when the oscillation output decreases. That is, when the Schmitt circuit detects a decrease in the oscillation output and reduces the resistance for amplitude adjustment, if the resistance for amplitude adjustment is too small, the oscillation output once decreased becomes again equal to or higher than the threshold value of the Schmitt circuit. Because. Therefore, in such an oscillation circuit, when an object approaches further from a state where the object approaches and the oscillation output decreases and the resistance for amplitude adjustment decreases,
Oscillation amplitude decreases, and if it approaches further, oscillation stops.

In order to solve the above-mentioned problem, a proximity switch as shown in FIG. 4 is known.

In this proximity switch, one transistor T1 of a current mirror circuit including transistors T1 and T2 is connected to a resonance circuit including the detection coil L and the capacitor C1. The emitters of the transistors T1 and T2 are connected to a power supply Vcc via resistors R11 and R21, each having the same resistance value. The collector of the transistor T2 is connected to the bases of the transistors T1 and T2, and is connected to 0 V of the power supply via the transistor T3 and the resistor R51. The resonance circuit is connected to a power supply Vcc via a resistor R31, diodes D1, D2 and a resistor R41, and a connection point between the resistor R31 and the diode D1 is connected to the base of a transistor T4. The transistor T4 is an emitter-follower transistor configured to be connected to the power supply of 0 V via the emitter resistor R61 and to be provided with the emitter resistor R61 to the transistor T3. The output of the resonance circuit is converted into a voltage signal by the transistor T4 and applied to the base of the transistor T3, whereby the collector current of the transistor T3 is positively fed back to the resonance circuit via the current mirror circuit. When the output voltage of the transistor T4 is applied to the base of the transistor T5, the emitter resistances R71 and R81 and the capacitor C
The signal is rectified by 2 and supplied to the comparator 21 and the output circuit 22. An operational amplifier 23 having an amplification factor α is connected to a connection point between the emitter resistors R71 and R81 of the transistor T5. Connected to the end. The output of this inverting amplifier 24 is a field effect transistor (hereinafter referred to as
FET25) connected to the gate of this FET25 and resistor R9
One series connection is connected in parallel to the emitter resistor R51 of the transistor T3.

In the proximity switch shown in FIG. 4, the output of the resonance circuit is smoothed and charged to the capacitor C2 as a voltage corresponding to the oscillation amplitude of the oscillation circuit via the transistors T4 and T5. This smoothing voltage also decreases. Then, the decrease in the smoothing voltage of capacitor C2 is
The output of the comparator 21 drives the output circuit 22 to transmit a detection signal to the outside. Meanwhile, the capacitor
When the smoothing voltage of C2 decreases, the gate voltage of FET 25 gradually increases by amplifiers 23 and 24. As a result, the resistance value of the FET 25 gradually decreases, and the resistance values of the amplitude adjustment resistors determined by the resistance values of the resistors R51 and R91 and the FET 25 gradually decrease. In this way, when the object approaches and the oscillation amplitude of the oscillation circuit decreases, the amplitude adjusting resistance is gradually reduced so that the oscillation is continued at a predetermined level even after the object is detected.

[Problems to be solved by the invention]

In the prior art described above, the response speed of the object detection can be improved by the oscillation circuit continuing to oscillate at a predetermined level even after the object approaches and detects the object. As is apparent, since two amplifiers and one FET are required to continue oscillation, the number of components is increased and the cost is increased, and the circuit configuration is complicated and it is difficult to reduce the size of the proximity switch. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide a proximity switch that eliminates the above-mentioned disadvantages of the conventional device and can improve the response speed of object detection with a simple circuit configuration.

[Means for solving the problem]

In order to achieve the above-described object, the present invention provides a first current mirror circuit, a second current mirror circuit, a resonance circuit including a detection coil, and a voltage applied to the resonance circuit when a voltage of the resonance circuit is applied to a base. A current, a resistor for oscillation amplitude adjustment connected to the emitter of the first transistor, and a collector connected to the collector and base of the input-side transistor of the second current mirror circuit. The emitter includes a series circuit of a second transistor connected to a power supply via an emitter resistor and the emitter resistor, and the collector of the first transistor is connected to the first transistor.
The collector of the output-side transistor of the second current mirror circuit is connected to the collector of the input-side transistor of the second current mirror circuit together with the emitter of the first transistor and the base of the second transistor. , The emitter of the output transistor of the second current mirror circuit is connected to the zero volt line together with the other end of the oscillation amplitude adjusting resistor, and the first current mirror circuit is connected to the oscillation amplitude A current obtained by adding the current flowing through the adjustment resistor and the collector current of the output transistor of the second current mirror circuit is input to the input transistor of the mirror circuit via the first transistor, and the current of the mirror circuit is The first transistor is connected to the resonance circuit connected to the collector of the output transistor. Ri and feedback input and current equivalent to a current, the base of the second transistor, wherein an output of said resonant circuit is configured to enter the emitter voltage of the first transistor is amplified.

(Operation)

According to the present invention, when the oscillation voltage of the oscillation circuit is high, a small current is supplied to the output side transistor of the current mirror circuit connected in parallel with the oscillation amplitude adjustment resistor, and the oscillation voltage of the oscillation circuit is When it is low, a large current flows. Therefore, when the oscillation voltage of the oscillation circuit drops, a large feedback current flows through the resonance circuit via the first current mirror circuit by the second current mirror circuit, and oscillation is maintained at a predetermined level.

〔Example〕

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In FIG. 1, transistors 1a and 1b are configured as a current mirror circuit 1, and the same current as the current flowing through the resistor R1 flows through the collector of the transistor 1b. The collector of the transistor 1b is connected to the collector and base of the transistor 2 and also to the bases of the transistors 6 and 10. That is, the current mirror circuit 1
Is a constant current source for supplying bias currents for the transistors 2, 6, and 10. A parallel resonance circuit including a detection coil 3 and a capacitor 4 is connected to the emitter of the transistor 2. The transistor 2 shifts the voltage generated in the resonance circuit in a DC manner. The transistors 5a and 5b are configured as a current mirror circuit 5, and the collector and base of the input side transistor 5a of the current mirror circuit 5 are connected to the collector of the transistor 6. On the other hand, the output side transistor of the current mirror circuit 5
The collector 5b is connected to a connection point of a resonance circuit including the emitter of the transistor 2, the detection coil 3 and the capacitor 4. The emitter of the transistor 6 is connected to 0 V of the power supply via the resistor R2.

The output side transistor 8b of the current mirror circuit 8
The input transistor 8a of the current mirror circuit 8 is connected in parallel with R2, and is connected to the power supply Vcc via the resistor R3 and the emitter / collector of the transistor 9. The base of the transistor 9 is connected to the connection point between the emitter of the transistor 6 and the resistor R2. The collector of the transistor 10 is the input side transistor 11a of the current mirror circuit 11.
Connected to the collector and base of this transistor
The 10 emitters are connected to 0 V of the power supply via a resistor R4. The output side transistor 11b of the current mirror circuit 11 has a resistance R
5 constitutes a series circuit, which is connected between the power supplies. Capacitor 12 and comparator in parallel with resistor R5
13 inputs are connected. The comparator 13 detects that the voltage between both ends of the capacitor 12 has dropped below a predetermined value, and its output is sent to the outside via an output circuit 14.

Next, the operation of the proximity switch shown in FIG. 1 will be described.

When a voltage is applied to the resonance circuit of the detection coil 3 and the capacitor 4 and the output voltage of the resonance circuit rises, the voltage is current-amplified by the transistors 6 and 10 and the resistance R2 and
Appears in R4. Then, the emitter voltage of the transistor 6 is
If Va, a current Va / R2 flows through the resistor R2. on the other hand,
A current of (Vcc−VBE−Va) / R3 flows through the collector of the transistor 9 (Vcc: power supply voltage, VBE: base-emitter voltage of the transistor 9). The collector current of the transistor 9 is transmitted by the current mirror circuit 8 to the output side transistor 8b of the current mirror circuit 8. Resistance R2
Current I1 flowing through the current mirror circuit 5 and the collector current I2 of the output side transistor 8b of the current mirror circuit 8 flow through the transistor 6 to the input side transistor 5a of the current mirror circuit 5, so that the current I1 and I2 are added from the current mirror circuit 5. The IF is fed back to the resonance circuit and oscillation continues. FIG. 2 shows the relationship between the emitter voltage Va of the transistor 6, the current I1 flowing through the resistor R2, the current I2 flowing through the output-side transistor 8b of the current mirror circuit 8, and the feedback current IF from the current mirror circuit 5.

If the detection object (not shown) is far from the detection coil 3, the loss of the resonance circuit is small and the resonance circuit oscillates with a large amplitude. Then, the emitter resistance R4 of the transistor 10
A current corresponding to the oscillation voltage also flows through the current mirror circuit 11, and the current flows to the resistor R5. The voltage across the resistor R5 is smoothed by the capacitor 12. Therefore, if the oscillation voltage of the resonance circuit is high, the voltage across the resistor R5 is also high, and the comparator 13
, No output is generated from the comparator 13. Further, the output of the output circuit 14 is also in the prohibited state.

Next, when the detection object approaches the detection coil 3, the loss of the resonance circuit increases, and the oscillation voltage decreases. If the oscillation voltage decreases, the current flowing through the emitter resistor R4 of the transistor 10 also decreases, and the current flowing through the resistor R5 via the current mirror circuit 11 also decreases.Therefore, the smoothing voltage of the capacitor 12 also decreases, and the input of the comparator 13 decreases. When the voltage decreases and falls below the threshold value, the output of the comparator 13 is output to the outside via the output circuit 14 as a detection signal. On the other hand, when the oscillation voltage of the resonance circuit decreases, the emitter voltage Va of the transistor 6 also decreases. As is apparent from FIG. 2, when the emitter voltage Va of the transistor 6 decreases, the current flowing through the resistor R2
I1 decreases, and the output side transistor 8b of the current mirror circuit 8
Collector current I2 increases. Therefore, since the feedback current IF of the resonance circuit determined by I1 + I2 decreases at a small change rate as compared with the decrease of the oscillation voltage, the oscillation voltage does not decrease rapidly but gradually decreases as the detection object approaches. Shows oscillation characteristics. FIG. 3 shows the relationship between the distance to the detection object and the oscillation voltage of the resonance circuit.

Further, when the detection object moves from the state where the detection object approaches the detection coil 3 and the resonance circuit oscillates at a low level to the state where the detection object moves away, the loss of the resonance circuit decreases and the feedback also occurs even when the oscillation level is low. Since the current is large, the oscillation voltage of the resonance circuit sharply increases, and the response speed of the detection object increases.

In the embodiment shown in FIG. 1, the base of the transistor 9 is connected to the emitter of the transistor 6, but a voltage corresponding to the oscillation voltage of the resonance circuit may be applied to the base of the transistor 9. Therefore, the base of the transistor 9 may be connected to the emitter of the transistor 10 or to the input of the comparator 13 in which the voltage corresponding to the oscillation voltage is smoothed.

〔The invention's effect〕

As described above, according to the present invention, a first current mirror circuit, a second current mirror circuit, a resonance circuit including a detection coil, a voltage of the resonance circuit is applied to a base, and a voltage of the resonance circuit is applied. A current, a resistor for oscillation amplitude adjustment connected to the emitter of the first transistor, and a collector connected to the collector and base of the input-side transistor of the second current mirror circuit. The emitter includes a series circuit of a second transistor connected to a power supply via an emitter resistor and the emitter resistor, and the collector of the first transistor is a collector and a base of an input-side transistor of the first current mirror circuit. And the collector of the output-side transistor of the second current mirror circuit is connected to the emitter of the first transistor and the With 2 of the transistor base is connected to one end of the resistor for the oscillation amplitude adjustment, the second
The emitter of the output-side transistor of the current mirror circuit and the other end of the oscillation amplitude adjusting resistor are connected to a zero volt line, and the first current mirror circuit includes a current flowing through the oscillation amplitude adjusting resistor and the second The current obtained by adding the collector current of the output transistor of the current mirror circuit is input to the input transistor of the mirror circuit via the first transistor, and the resonance connected to the collector of the output transistor of the mirror circuit. A current equivalent to the current input from the first transistor is fed back to the circuit, and the emitter voltage of the first transistor whose output of the resonance circuit is amplified is input to the base of the second transistor. As a result, the oscillation circuit continues to oscillate at a predetermined level even when the detection object approaches,
Even when the detecting object moves away from the state where the detecting object approaches and the oscillation circuit oscillates at a predetermined level, the oscillation current can be rapidly raised because the feedback current to the oscillating circuit is large. Therefore, there is an effect that a high response speed of a detected object can be obtained with a simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a high-frequency oscillation type proximity switch showing one embodiment of the present invention, and FIG. 2 shows a relationship between an emitter voltage and an emitter current of a transistor 6 and a feedback current of a current mirror circuit 5 in FIG. FIG. 3 is a graph showing a relationship between a distance to a detection object and an oscillation voltage, and FIG. 4 is a circuit diagram of a proximity switch showing a conventional device. 3: Detection coil, 4: Capacitor, 1, 5, 8, 11: Current mirror circuit, 2, 6, 9, 10: Transistor, 13: Comparator, 14: Output circuit, R1 to R5: Resistance.

Claims (1)

(57) [Claims] 1. A first current mirror circuit, a second current mirror circuit, a resonance circuit including a detection coil, and a voltage which is applied to a base and converts the voltage of the resonance circuit into a current. A transistor, an oscillation amplitude adjusting resistor connected to the emitter of the first transistor, and a collector connected to the collector and base of the input-side transistor of the second current mirror circuit, and the emitter connected via an emitter resistor. And a series circuit of a second transistor connected to a power supply and the emitter resistor. A collector of the first transistor is connected to a collector and a base of an input-side transistor of the first current mirror circuit. The collector of the output side transistor of the current mirror circuit is connected to the emitter of the first transistor and the base of the second transistor. Both are connected to one end of the oscillation amplitude adjusting resistor, the emitter of the output-side transistor of the second current mirror circuit is connected to the zero volt line together with the other end of the oscillation amplitude adjusting resistor, and the first current mirror The circuit is configured such that a current obtained by adding a current flowing through the oscillation amplitude adjustment resistor and a collector current of an output transistor of the second current mirror circuit is input to an input transistor of the mirror circuit via the first transistor. Then, a current equivalent to the current input from the first transistor is fed back to the resonance circuit connected to the collector of the output side transistor of the mirror circuit, and the resonance circuit of the resonance circuit is connected to the base of the second transistor. A high-frequency oscillation type near-infrared oscillator, wherein an emitter voltage of the first transistor whose output is amplified is input; Switch.