JPH0422047B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to an output circuit that is used in, for example, a proximity switch and can switch an output signal on and off.

(b) Background of the Invention A conventional high-frequency oscillation type proximity switch that is generally well known consists of an oscillation circuit, a detection circuit that detects the output of this oscillation circuit, a comparator that compares the output of the detection circuit with a reference voltage, and a comparator that compares the output of the detection circuit with a reference voltage. It consists of an output circuit that outputs an ON or OFF signal based on the comparator output. Under normal conditions, when no detection object arrives, the oscillation circuit oscillates, and the detection circuit generates a detection output corresponding to the oscillation output. Since the voltage from the detection circuit is higher than the reference voltage, its output side is turned off, and as a result, the output circuit also outputs an off signal, that is, a non-detection signal of a nearby object. When the sensing object approaches, the conductance of the coil of the oscillation circuit changes, and the amplitude of the oscillation of the oscillation circuit decreases, or oscillation stops, and as a result, the voltage from the detection circuit becomes smaller than the reference voltage, and the output of the comparator decreases. In response, the output circuit also turns on, and the output circuit outputs an on signal, that is, a nearby object detection signal.

The circuit for this type of proximity switch is shown in FIG. In the same figure, 1 is the coil L and the capacitor C.
2 is a detection circuit, 3 is a comparator circuit including a comparator CP, and 4 is an output circuit. Comparator CP is of normally open type. The output circuit 4 is composed of transistors TR1 and TR2, a light emitting diode LED as an operation indicator, and the output terminal of the comparator CP is connected to the base electrode of the transistor TR1 via a resistor R1. The diode LED and the resistor R4 are connected in series and connected between the power supply terminal 5 and the common terminal 7. Furthermore, a transistor is connected between the connection point of the light emitting diode LED and the resistor R4.
The base electrode of TR2 is connected. When providing the output circuit 4 of this proximity switch with an on/off (normally closed/normally open) output switching function, the output terminal of the comparator CP, the resistor R3, and the light emitting diode are connected as shown in the figure.
It is conceivable to connect a changeover switch SW between the connection points of the LEDs.

In the output circuit to which the changeover switch SW is connected, when the changeover switch SW is off, the output of the comparator CP is off (H level), that is, when the sensing object is not close and the oscillation circuit 1 is in the oscillation state. is transistor TR1 is off,
Therefore, the light emitting diode LED does not light up and no current flows through the resistor R4, so the transistor TR2
It doesn't turn on either. On the other hand, when the output of the comparator CP turns on (L level), that is, when the sensing object approaches and the oscillation circuit 1 stops oscillating, the transistor TR1 turns on, and therefore the light emitting diode LED also lights up, and the resistor R4 Since current flows through the transistor TR2, the transistor TR2 is also turned on. In this case, the switch SW operates normally as normally open.

On the other hand, when the switch SW is on, the output of the comparator CP is off, and the transistor TR1 is always on, and the resistors R1, R2, R3 and the transistor
Equivalently, the circuit consisting of TR1 becomes a resistor, and the light emitting diode LED lights up, and the transistor TR2 is also turned on. That is, when the output of the comparator CP is H (sensing object not approaching), an on-current flows through the transistor TR2, and the output is inverted. Some disadvantages arise in this case. First, considering the conventional wisdom that the operation indicator light is turned on when the sensing object approaches, in the above case, the lamp is turned on when the sensing object is not approaching, resulting in reverse lighting. In addition, the output of transistor TR1 is connected to the oscillation circuit 1.
If this signal is used as a drive signal for the transistor TR3, which adds hysteresis to the oscillation amplitude, the transistor TR3 will be driven in the opposite direction, making the operation unstable. Furthermore, when the output of the comparator CP becomes a complementary output, a short circuit occurs when the switch SW is turned on, and the comparator CP is damaged.

(c) Purpose of the Invention The purpose of the present invention is to solve the above-mentioned disadvantages all at once and to provide an output circuit which can operate normally without any contradiction even if a switch for changing the output is provided.

(d) Structure and Effects of the Invention In order to achieve the above object, the output circuit of the present invention inputs a signal from a comparator that derives an on output or an off output depending on whether the input signal level is higher than a reference level. an operation indicator connected in series to the first transistor, a second transistor to which the output of the comparator is applied via a diode, and an input of the second transistor; a third transistor that outputs a signal according to the output of the comparator and whether the switch is on or off, and an output side connection of the output of the second transistor; and an impedance element connected between the end and the input electrode of the third transistor.

According to the output circuit of the present invention, the transistor (first) that turns on and off the operation indicator light according to the output of the comparator and the transistor (second) to which the output changeover switch is connected are configured separately. The operation indicator light can be turned on when a nearby object approaches without switching the operation indicator light on and off. In addition, the output of the transistor that turns on and off this operation indicator light,
If the transistor for hysteresis is driven, an appropriate hysteresis can be obtained regardless of the switching of the switch. Furthermore, since the output of the comparator is applied to the input of the second transistor via the diode, when the switch is turned on, the base current of the first transistor flows through the switch, so that it is always on regardless of the output of the comparator. This also prevents short-circuiting through the switch when the comparators have complementary outputs.

(e) Description of Examples The present invention will be explained in more detail below using Examples.

FIG. 2 is a circuit diagram of a proximity switch in which the present invention is implemented.

In FIG. 2, the same reference numerals as those shown in FIG. 1 indicate the same components. The difference between this figure and the one shown in FIG. 1 is that a diode D2 is connected instead of the light emitting diode LED connected between the resistor R3 on the collector side of the transistor TR1 of the output circuit 4 and the base electrode of the transistor TR2. In addition, a series circuit consisting of transistor TR4, resistor R7, and light emitting diode LED was connected in parallel to transistor TR1, and the output of comparator CP was connected to the base electrode of transistor TR4 via resistor R5. The diode D1 is connected between the output terminal of the comparator CP and the connection point between the resistor R1 and the switch SW. The signal that drives the hysteresis transistor TR3 is as follows:
It is taken out from the connection end between transistor TR4 and resistor R7.

Next, the operation of the embodiment circuit shown in FIG. 2 will be explained.

When the switch SW is off, the comparator
When the CP output is off (sensing object is not approaching), both transistors TR1 and TR4 are off.
Therefore, the light emitting diode LED does not light up,
Also, since no current flows through resistor R4, the transistor
TR2 doesn't turn on either. When the comparator CP output is on (sensing object approaches), transistor TR1,
TR4 is both turned on, so resistor R7,
A current flows through the light emitting diode LED, lighting up the light emitting diode LED, and a current also flows through the resistor R4, turning on the transistor TR2. In this case, when the switch SW is turned off, the circuit performs a normally open operation, which is similar to the circuit shown in FIG. 1 in this respect.

On the other hand, when the switch SW is turned on and the comparator CP is turned off, the transistor TR4
is off and the light emitting diode LED does not light up.
Also, transistor TR1 is turned on by switch SW,
A current flows through the diode D2 and the resistor R4, and the current at this time has a value sufficient to turn on the transistor TR2, so it is turned on. In other words, the switch
When SW is turned on, the transistor TR2 is turned on when the output of the comparator CP is off, that is, when the sensing object is not approaching.

In this case, if the diode D1 is not provided, the base current of the transistor TR4 will be
The current flows through the resistor R5, the switch SW, the diode D2, and the resistor R4 and is always turned on regardless of whether there is an output from the comparator CP, but the diode D1 prevents this current from flowing. In addition, diode D1 is connected to switch SW when comparator CP is complementary output.
This prevents a short circuit from occurring.

Next, when the switch SW is also turned on and the comparator CP is on, both transistors TR4 and TR1 are turned on, so the light emitting diode LED lights up, and the transistor
Transistor for hysteresis control using the output signal of TR4
TR3 is turned on and the oscillation conditions of the oscillation circuit 1 are made stricter to prevent the oscillation that has stopped once due to the detection of a nearby object from repeating the unstable state of oscillation and stop. Also, transistors TR4 and TR1 are turned on, but the forward voltage of diode D1 and the transistor
Diode D whose forward voltage between the base and emitter of TR2 is approximately equal and whose forward voltage is greater than the saturation voltage of the output of comparator CP.
2 is connected between the switch SW and the base electrode of the transistor TR2, the voltage across the resistor R4, that is, the voltage applied to the base of the transistor TR2, is not sufficient to turn on the transistor TR2. Transistor TR2
is in the off state. When the switch SW is turned on in this way, the output of the comparator CP is on, which means that the output of the transistor TR is in the vicinity of the sensing object.
2 is off.

As described above, in this embodiment circuit, the proximity output of the detected object can be derived as an on signal or an off signal by turning on/off the changeover switch SW. Furthermore, the operation indicator LED is turned on when a sensing object arrives, regardless of whether the changeover switch SW is on or off, and furthermore, hysteresis control can be performed without contradiction.

In addition, in the embodiment shown in FIG.
A diode D2 is connected to cancel the current of 1, but instead of this diode D2, another impedance element such as a resistor R8 is connected as shown in FIG.
The resistance value of the resistor R8 may be selected so that the voltage divided by R4 and R8 is smaller than the voltage that turns on the transistor TR2. The other parts of the circuit shown in FIG. 3 are similar to the circuit shown in FIG.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional proximity switch, FIG. 2 is a circuit diagram showing a proximity switch in which the present invention is implemented, and FIG. 3 is a circuit diagram of an output circuit of a proximity switch showing another embodiment. . 4...Output circuit, CP...Comparator, TR1
...Transistor (second), TR2...Transistor (third), TR4...Transistor (first),
LED...light emitting diode, SW...changeover switch, D1, D2...diode, R8...resistance.

Claims (1)

[Claims] 1. A first transistor to which the output of a comparator that derives an on-output or an off-output depending on whether the input signal level is equal to or higher than a reference level is applied to the input, and a first transistor connected in series with the first transistor. an operation indicator light to be connected, a second transistor to which the output of the comparator is applied to the input via a diode, a switch connected between the input side and the output side of the second transistor, and the output of the comparator. and a third transistor that outputs a signal according to on/off of the switch, and an impedance element connected between the output side connection terminal of the second transistor of the switch and the input electrode of the third transistor. output circuit. 2. The output circuit according to claim 1, wherein the impedance element is a diode. 3. The output circuit according to claim 1, wherein the impedance element is a resistor.