JPH0744103Y2 - Proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to proximity switches, and in particular to their snap characteristics.

[Prior Art] A conventional proximity switch of this type is shown in FIG. In the figure, 1 is an oscillator circuit, C1, C2, C3 are capacitors, R1, R2, R3 are resistors, D1 is a light emitting diode, and Tr1, Tr2 are transistors.

In the proximity switch having such a configuration, when an object to be detected (not shown) approaches the oscillation circuit 1 and enters a detection state, the output of the oscillation circuit 1 becomes a low potential level, and when the object to be detected moves away, an oscillation output appears. When the oscillation signal exceeds a predetermined level, the transistor Tr1 repeats on / off. At this time, the capacitor C2 is repeatedly charged and discharged, but the capacitor C2
Has a relatively large capacitance, and the capacitor C2
The discharging operation is performed in the state that the charging potential of is hardly raised, and the collector of the transistor Tr1 is almost at the ground potential. Therefore, the transistor Tr2 is turned off,
The output is taken out between terminals 2 and 3.

[Problems to be Solved by the Invention] In the conventional proximity switch shown in FIG. 3 as described above, the rising and falling characteristics of its output depend on the snap characteristics of the oscillation circuit 1 itself, and accordingly, It is very difficult to design an oscillation circuit to obtain the snap characteristics required to operate as a switch, and the snap characteristics (rising and falling) are several + μse due to the mounting of the oscillation circuit.
c was the limit.

Further, in the case where the detection circuit a and the Schmitt circuit b shown in FIG. 4 are separately configured, the snap characteristic is improved by the action of the Schmitt circuit, but the number of parts is increased accordingly, and a small and inexpensive proximity switch is obtained. It was not suitable as a circuit configuration for.

The present invention has been made in order to solve such a problem, and can improve output rise and fall characteristics without considering snap characteristics of an oscillator circuit and without increasing the number of components. The object is to obtain an improved inexpensive proximity switch.

[Means for Solving Problems] A switch according to the present invention includes an oscillation circuit that stops oscillation when an object to be detected approaches and oscillates when the object to be detected moves away, and outputs an oscillation signal from an output terminal, and a resistor. And a first capacitor are connected in series, the terminal of the resistor on the side opposite to the connection point with the first capacitor is connected to the positive side of the power supply, and the side opposite to the connection point on the first capacitor with the resistance. The terminal of consists of a high-pass filter connected to the output terminal of the oscillation circuit and a pnp-type transistor, the base is connected to the connection point between the resistor of the high-pass filter and the first capacitor, and the oscillation signal passes through the first capacitor. First input to the base via
And a pnp-type transistor,
The emitter is connected to the emitter of the first transistor,
A Schmitt circuit including a second transistor whose base is connected to the collector of the first transistor, a second capacitor connected in parallel between the emitter and collector of the first transistor, and a switching output of the second transistor. And an output circuit driven by.

[Operation] In the present invention, in the Schmitt circuit formed by the first transistor and the second transistor, the first
Since the Schmitt circuit is configured to have a detection function by connecting a capacitor in parallel between the collector and the emitter of the transistor, the output rise and fall characteristics are improved with a simple circuit configuration.

[Embodiment] FIG. 1 is a circuit diagram of a proximity switch according to an embodiment of the present invention, and FIG. 2 is a time chart showing its operation. In the figure, reference numeral 1 denotes an oscillating circuit, which is a system for stopping oscillation when an object to be detected approaches. A high-pass filter circuit is configured by the capacitor C11 and the resistor R11. In addition, a Schmitt circuit is composed of the pnp type transistors Tr11 and Tr12 and the resistors R12 to R14, and a capacitor C12 is connected in parallel between the collector and emitter of the transistor Tr11 to form a switching circuit that also has a detection function. ing. The transistor Tr13 is a transistor forming an output circuit, and its input (base) side and the output of the transistor Tr12 are connected via a light emitting diode D11. Here, R15 is a bleeder resistance.

In the proximity switch configured as described above, in the detection state in which the object to be detected approaches the oscillation circuit 1, the oscillation circuit 1 stops oscillation and its output is 0 (earth potential). In this state, the output of the high-pass filter, that is, the base potential A is high, and the transistor Tr11 is off. Therefore, the base potential B of the transistor Tr12 becomes low, the transistor Tr12 is in the ON state, and the capacitor C12 is charged to the potential corresponding to the base-emitter of the transistor Tr12. Then, when the transistor Tr12 is turned on, the light emitting diode D11 is driven to emit light, and further, a drive voltage is applied to the base of the transistor Tr13 via the light emitting diode D11, the transistor Tr13 is turned on, and the output terminals 2 and 3 are connected. Short-circuit output can be obtained.

Next, when the oscillation circuit goes into the non-detection state from this state, an oscillation signal appears at the output of the oscillation circuit 1 and is applied to the base of the transistor Tr11 via the capacitor C11,
The potential A pulsates as shown in FIG. When this oscillation signal falls below a certain level, the transistor
Tr11 is turned on, whereby the collector-emitter of transistor Tr11 is almost short-circuited and transistor Tr12 is turned off. In this case transistor Tr11
The signal applied to the base of sine draws a sine curve. Therefore, the transistor Tr11 repeatedly turns on and off based on the cycle of the sine curve.

However, the transistor Tr that constitutes this Schmitt circuit
Since there is a capacitor C12 between the collector and the emitter of 11, even if the transistor Tr11 is turned off,
The base potential B applied to Tr12 does not fall to the potential that turns on the transistor Tr12. That is, when the voltage applied to the base of the transistor Tr11 becomes equal to or lower than the threshold value, the transistor Tr11 is turned on, and thus the capacitor C1
The charge of 2 is discharged along the path of the collector → emitter of the transistor Tr11. Further, when the sine curve exceeds the threshold value, the transistor Tr11 is turned off, and at this time, the capacitor C12 is charged through the route of the resistor R12 → the capacitor C12 → the resistor R13. At this time, if the voltage applied to the capacitor C12 becomes equal to or higher than the base-emitter voltage of the transistor Tr12, the transistor Tr12 can be turned on. Since its operation is reversed, the charge of the capacitor C12 is
Discharged in the collector-emitter path of 1. Therefore,
The base potential B of the transistor Tr12 does not drop until the transistor Tr12 is turned on (see FIG. 2 (B)), and this state is repeated, so that the transistor Tr11
Even if an oscillation signal is applied to the base of the transistor Tr12
Turns off. Then, because the transistor Tr12 is turned off, the light emitting diode D11 is not driven, the transistor Tr13 is also turned off, and a release output is obtained from between the output terminals 2 and 3,
It is understood that it is in the non-detection state.

Since the Schmitt circuit including the transistors Tr11 and Tr12 is fed back by the resistor R12, the snap characteristic of the output signal is significantly improved even if the rise and fall of the signal applied to the transistor Tr11 is not good. ing. In this case, the charging time constant of the capacitor C12 is set to a value sufficiently larger than the oscillation frequency of the oscillation circuit.

Further, when shifting from the non-detection state to the detection state again, as described above, when the oscillation of the oscillation circuit 1 is stopped, the transistor Tr11 is turned off and the transistor Tr12 is turned on,
Short-circuit output can be obtained from output terminals 2 and 3.

[Effects of the Invention] As described above, the present invention has the transistors Tr11 and Tr12.
Also, since the Schmitt circuit has a circuit configuration in which the Schmitt circuit has a detection function by the capacitor C12, the output rise and fall characteristics are remarkably improved with a simple configuration, and an inexpensive proximity switch with a simple circuit configuration can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a proximity switch according to an embodiment of the present invention, FIG. 2 is a time chart showing its operation, and FIGS. 3 and 4 are circuit diagrams of conventional proximity switches. 1 ... Oscillation circuit R11, C11 ... High-pass filter Tr11 ... First transistor Tr12 ... Second transistor C12 ... Capacitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-90426 (JP, A) JP-A-48-18763 (JP, A) Actual development Sho-59-46030 (JP, U) JP-B-51- 40930 (JP, B2) Actual public 41-4747 (JP, Y1) Actual public 56-41316 (JP, Y2)

Claims (1)

[Scope of utility model registration request] 1. An oscillation circuit, which stops oscillation when an object to be detected approaches, and oscillates when the object to be detected goes away, and outputs an oscillation signal from an output terminal, a resistor and a first capacitor are connected in series, and the resistor is connected. First of
The terminal on the side opposite to the connection point with the capacitor is connected to the positive side of the power source, and the terminal on the side opposite to the connection point with the resistor of the first capacitor is connected to the output terminal of the oscillation circuit. A high-pass filter and a pnp-type transistor, a base is connected to a connection point between the resistance of the high-pass filter and the first capacitor, and the oscillation signal is input to the base via the first capacitor. A Schmitt circuit including a first transistor and a pnp-type transistor, the emitter of which is connected to the emitter of the first transistor, and the base of which is connected to the collector of the first transistor; A second capacitor connected in parallel between the emitter and collector of the first transistor, and a switching output of the second transistor Proximity switch and having an output circuit which is more driven.