JP3430681B2 - DC two-wire sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC two-wire sensor, and more particularly to a DC two-wire sensor characterized by its output circuit.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing an example of a conventional DC two-wire sensor. In this figure, a load 3 and a DC power supply 4 are connected in series between terminals 1 and 2. In the DC two-wire type sensor, an internal constant voltage circuit 5 is provided between terminals 1 and 2.
Are connected to supply constant voltage to each part. When this DC two-wire sensor is used as a high-frequency oscillation type proximity sensor, an oscillation circuit 6 that has a coil inside the sensor and whose oscillation state changes according to the proximity of an object, and the output thereof is rectified and discriminated by a predetermined threshold value. The discrimination circuit 7 is provided. The output of the discrimination circuit 7 is input to the signal processing circuit 8. The signal processing circuit 8 determines the presence or absence of an object based on the signal from the discrimination circuit 7,
It is output through the output circuit 9. Here, the oscillation circuit 6, the discrimination circuit 7, and the signal processing circuit 8 constitute a sensor circuit section that outputs the ON and OFF states of the DC two-wire sensor. A constant voltage circuit 9a and an output switching transistor 9b are provided in the output circuit 9. The output constant voltage circuit 9a is slightly higher than the constant voltage of the internal constant voltage circuit 5, and holds the residual voltage for operating the internal circuit when the transistor 9b is turned on.

In such a conventional DC two-wire sensor,
The internal constant voltage circuit 5 and the output circuit 9 require the constant voltage circuit 9a for holding the residual voltage. Since the circuit scale of the constant voltage circuit is large, if the entire DC two-wire sensor is to be integrated into an IC, a large area will be taken within the IC. Conventionally, two constant voltage circuits are required, and there is a drawback that the price when integrated into an IC increases. Further, since each of these constant voltage circuits has variations, there is also a drawback that when the output is turned on, the level of the voltage supplied decreases due to the fluctuation of the power supply and the internal circuit may not operate.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and a two-wire direct current circuit in which the circuit scale is reduced by switching one constant voltage circuit and switching the circuit. An object of the present invention is to provide a sensor.

[0005]

According to a first aspect of the present invention, a load and a DC power source are connected in series between the first and second terminals, and the first and second terminals are opened and closed. In a DC two-wire sensor that performs a switching operation by a sensor circuit unit that outputs an on / off signal, a constant voltage circuit that supplies a constant voltage to the sensor circuit unit, and the constant voltage circuit when the output of the sensor circuit unit is off. A first bias current source for supplying a bias current to the constant voltage circuit, a second bias current source for supplying a bias current to the constant voltage circuit when the output of the sensor circuit section is on, and an output of the sensor circuit section. And a switching element for switching between the first and second terminals by the output of the sensor circuit section and a switching section for switching the source, and holding an output residual voltage higher than the voltage of the constant voltage circuit. An output circuit for controlling the bias current, the output circuit being driven by the output of the constant voltage circuit, the bias current adjusting first transistor for adjusting a bias current, the input terminal of the constant voltage circuit, and the bias circuit. A first diode connected between the collector of the first transistor for current adjustment and the first bias current source, wherein the first bias current source is a first terminal and an input terminal of the constant voltage circuit. Second with collector and emitter connected to each
And a resistor connected between the collector and the base of the second transistor, wherein the second bias current source is an emitter between the first terminal and the constant voltage circuit. And the third with the collector connected
And a series connection of a transistor and a resistor, the surplus current of the first bias current source is directly supplied, and the surplus current of the second bias current source is supplied to the bias current via the first diode. It is characterized in that the voltage is supplied to the first transistor for adjustment. The invention of claim 2 of the present application is a DC two-wire system in which a load and a DC power supply are connected in series between the first and second terminals, and a switching operation is performed by opening and closing between the first and second terminals. In the sensor, a sensor circuit unit that outputs an on / off signal, a constant voltage circuit that supplies a constant voltage to the sensor circuit unit, and a first bias circuit that supplies a bias current to the constant voltage circuit when the output of the sensor circuit unit is off. Bias current source, second bias current source that supplies a bias current to the constant voltage circuit when the output of the sensor circuit unit is on, switching unit that switches these bias current sources according to the output of the sensor circuit unit, and the sensor circuit According to the output of the section,
An output circuit that has a switching element that opens and closes between second terminals, and that holds an output residual voltage higher than the voltage of the constant voltage circuit, wherein the first bias current source is the first bias current source.
And a resistor connected between the collector and the base of the second transistor, and a resistor connected between the collector and the emitter of the constant voltage circuit and the input terminal of the constant voltage circuit, respectively. Is driven by the output of the constant voltage circuit, and includes a first transistor for bias current adjustment that adjusts a bias current, an input terminal of the constant voltage circuit, and a collector of the first transistor for bias current adjustment. A second diode connected in series between a first diode connected between the first diode and a base terminal of a second transistor constituting the first bias current source and a collector of the first transistor for bias current adjustment. , Third
The second bias current source is connected in series between the first terminal and the constant voltage circuit, and the third transistor and the resistor are connected in series. And has the first
The excess current of the bias current source is supplied to the first transistor for bias current adjustment via the second and third diodes, and the excess current of the second bias current source is supplied to the first transistor for bias current adjustment via the first diode. It is characterized by doing so.

[0006]

According to the present invention having such a feature, when the output of the sensor circuit section is in the OFF state, the constant voltage circuit is supplied with power from the first bias current source and the constant voltage is supplied to each block. When the output of the sensor circuit unit is turned on, power is supplied from the second bias current source to the constant voltage circuit, and the output terminal is held at an output residual voltage higher than that of the constant voltage circuit. In this way, by switching the first and second bias current sources, a constant voltage circuit is used to constantly supply a constant voltage to each unit, and the output residual voltage in the ON state is maintained at a value higher than the constant voltage. I am trying.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a basic configuration diagram showing a DC two-wire sensor according to an embodiment of the present invention, particularly showing in detail an output circuit and a constant voltage circuit part. In this figure, the same parts as those of the conventional example described above are designated by the same reference numerals, and detailed description thereof will be omitted. In the DC two-wire sensor according to this embodiment, the load 3 and the DC power supply 4 are connected between the terminals 1 and 2 as in the conventional example. A resistor R1 and a transistor Q1 are connected in series to the terminal 1 as shown. Transistor Q across resistor R1
The two collectors and bases are connected to each other, and the emitters thereof are grounded via the resistors R2 and R3, and are also connected to the resistor R4. In addition, terminals 1 and 2 have PNP transistor Q3
Q4 and the resistor R5 are connected in series. A resistor R6 is connected between the base and the emitter of the transistor Q3, and the transistor Q6 is connected to the resistor R6 in series via a resistor R7. The detection signal from the signal processing circuit 8 described above is input to the base of the transistor Q6. The other end of the resistor R4 is connected to the emitter of the transistor Q4,
Its base is connected to the midpoint of resistors R2 and R3. The collector of the transistor Q4 is connected to the base of the transistor Q5. The transistor Q5 is a transistor for opening and closing between the terminals 1 and 2, and its emitter is at the terminal 2,
The collector is connected to terminal 1. Here, the resistor R1 and the transistor Q2 constitute a first bias current source, the transistors Q3 and Q4 and the resistor R4 constitute a second bias current source, and the first diode D1 switches these. Also, transistors Q3 and Q5, resistors R5 and R6,
R7 is an element for controlling the output, transistor Q4, resistors R2 and R3 are elements for creating a reference voltage of the output voltage,
The transistor Q1 is a transistor for adjusting the bias current.

Next, the operation of this embodiment will be described. When the output of the signal processing circuit 8 is at L level, the transistors Q3, Q4, Q5 and Q6 are all in the off state,
The second bias current source consisting of the transistors Q3, Q4 and the resistor R4 is not operating. At this time, the transistor Q2 is turned on by the resistor R1, and the emitter current of the transistor Q2 flows into the constant voltage circuit 5. The transistor Q1 is in the ON state, and a surplus current of the current flowing through the resistor R1 excluding the base current of the transistor Q2 flows into the transistor Q1. The base current of the transistor Q2 is controlled to 1 / hfe of the current consumed by the constant voltage circuit 5.

When an object is detected and the output of the signal processing circuit 8 becomes H level, the transistor Q6 is turned on and all the transistors Q3, Q4 and Q5 are turned on. At this time, power is supplied from the transistor Q3 to the internal constant voltage circuit 5. The constant voltage circuit 5 outputs a constant voltage of 2.3 V, for example. Here, the potential at the midpoint of the resistors R2 and R3 is, for example, 2
If the voltage division ratio of the resistors R2 and R3 is set to V, the voltage across the resistor R2 becomes 0.3V. When the transistor Q4 is in the ON state, the emitter-base voltage thereof is about 0.7V, so that the voltage across the resistor R4 is 0.4V and the emitter voltage of the transistor Q4 is 2.7V. Here, by appropriately selecting the resistor R6, the transistor Q3 is saturated when it is in the ON state, and its emitter-collector voltage is set to approximately 0 V, so that the voltage at the terminal 1 can be regulated by the constant voltage circuit 5. The voltage can be 2.7V. At this time, a current flows from the DC power supply 4 to the load 3 through the transistor Q5, and the load 3 is driven.

Next, a second embodiment, which is a more specific structural example of the DC two-wire sensor according to the present invention, will be described with reference to FIG. In this figure, the same parts as those in the first embodiment described above are designated by the same reference numerals and detailed description thereof will be omitted. In FIG. 2, the constant voltage circuit 5 is a bandgap circuit including transistors Q7 to Q11, and a constant voltage,
For example, it supplies a constant voltage of 2.3V. The output of the constant voltage circuit 5 supplies a constant voltage to the oscillation circuit 6, the discrimination circuit 7 and the signal processing circuit 8 which form the sensor circuit section. Transistor Q1 of this constant voltage circuit 5
The base of the transistor Q1 described above is connected to the emitter of 1. The collector of the transistor Q1 is connected to the common connection point of the resistors R4 and R2 and the emitter of the transistor Q2 via the diode D1 as in the first embodiment. In this embodiment, the second and third diodes D2 and D3 are connected in series to the other end of the resistor R1, and the cathode end of the diode D3 is commonly connected to the cathode of the diode D1 and is connected to the collector of the transistor Q1. . On the output side, a transistor Q12 is connected to the collector of the transistor Q4, and a Darlington-connected transistor Q13 is further connected. The transistors Q12 and Q13 are output transistors.

Next, the operation of this embodiment will be described. Also in this embodiment, when the output of the signal processing circuit 8 is at the L level, the transistor Q6 is in the off state, and no current flows through the resistor R6. At this time, the transistors Q3, Q4, Q
12, Q13 are off. At this time, the transistor Q2 becomes conductive, and the emitter current flowing through the transistor Q2 is supplied to the constant voltage circuit 5. A part of the current flowing through the resistor R1 is supplied as the base current of the transistor Q2, and the rest is supplied to the transistor Q1 via the diodes D2 and D3. At this time, the voltage between the base and the emitter of the transistor Q2 becomes a little larger than the forward voltage drop of each of the diodes D2 and D3. Therefore, although the diode D1 is forward biased, the flowing current is a small value. Become. Here, if the voltage of the DC power supply 4 is set to 24V, the terminal 1 is connected to the terminals shown in FIGS.
As shown in, a voltage of approximately 24 V appears as it is.

When an object is detected and the output of the signal processing circuit 8 becomes H level, the transistor Q6 is inverted and turned on. Therefore, transistors Q3, Q4, Q12, Q
13 is also turned on. At this time, similarly to the first embodiment described above, the output voltage of the constant voltage circuit 5 becomes 2.3V, and the emitter voltage of the transistor Q4 and the voltage at the terminal 1 also become 2.7V. Therefore, the transistor Q2 is turned off. At this time, a part of the collector current of the transistor Q3 is a resistor R
It is supplied to the constant voltage circuit 5 via 4. Of the current, an unnecessary current component in the constant voltage circuit 5 flows into the transistor Q1 via the diode D1. At this time, since the potential difference between both ends of the diodes D2 and D3 is 1.4 V or less,
No current flows through the diodes D2 and D3. In this way, the diode D1 and the diodes D2 and D3 are alternately switched. In this way, the diode D1 was forward biased when the output changed from the off state to the on state as shown in FIG.
The ringing of the voltage generated at the terminal 1 can be reduced as shown in FIG.

FIG. 4 is a diagram showing an output circuit portion of a DC two-wire sensor according to a third embodiment of the present invention. In this embodiment, the same parts as those in the second embodiment described above are designated by the same reference numerals, and detailed description thereof will be omitted. In this embodiment, the transistor Q1
2 and the base are common, and the emitter is the transistor Q13.
There is provided a negative feedback transistor Q14 connected to the base of the. The collector of the transistor Q14 is connected to the collector of the transistor Q3. This transistor Q1
Reference numeral 4 gives a negative feedback to the ON state of the transistor Q4, and can further suppress the output undershoot and ringing due to the inrush current when the transistors Q4, Q6, Q12 and Q13 are turned on.

Next, a fourth embodiment of the present invention will be described. In this embodiment, the constant voltage circuit 5A is replaced with the bandgap circuit shown in FIG. 2 and is constituted by a series connection body of diodes. By doing this, the base of the transistor Q1
In addition to the forward drop voltage between the emitters, the number of stages of a plurality of connected diodes × 0.7 V becomes an internal constant voltage of the constant voltage circuit and is supplied to each block of the DC two-wire switch. The configuration on the output side is the same as in the second embodiment.
In this case, the constant voltage circuit can be configured with an extremely simple structure, and the effect that the output residual voltage when the output is on can be regulated to a predetermined value is obtained.

[0015]

As described above in detail, according to the present invention, the DC two-wire sensor can have only one constant voltage circuit, and the circuit scale can be greatly reduced.
Therefore, the chip size when integrated into an IC is reduced, and the cost can be reduced. Further, the relationship between the internal constant voltage and the output residual voltage can be defined by using one constant voltage circuit, and the output oscillation state can be eliminated by fixing the output of the constant voltage circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the configuration of a DC two-wire sensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a constant voltage circuit and an output circuit of a DC two-wire sensor according to a second embodiment of the present invention.

FIG. 3 is a waveform diagram showing changes in the output state of the DC two-wire sensor according to the second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a constant voltage circuit and an output circuit of a DC two-wire sensor according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a constant voltage circuit and an output circuit of a DC two-wire sensor according to a fourth embodiment of the present invention.

FIG. 6 is a block diagram showing an overall configuration of a conventional DC two-wire sensor.

[Explanation of symbols]

1, 2 terminals 3 load 4 DC power supply 5,5A constant voltage circuit 6 oscillator circuit 7 Discrimination circuit 8 Signal processing circuit

Claims (4)

(57) [Claims] 1. A DC two-wire sensor, in which a load and a DC power supply are connected in series between first and second terminals, and which performs switching operation by opening and closing between the first and second terminals, on / off A sensor circuit section that outputs a signal; a constant voltage circuit that supplies a constant voltage to the sensor circuit section; a first bias current source that supplies a bias current to the constant voltage circuit when the output of the sensor circuit section is off; A second bias current source that supplies a bias current to the constant voltage circuit when the output of the sensor circuit unit is on, a switching unit that switches between the bias current sources according to the output of the sensor circuit unit, and an output of the sensor circuit unit. The first and second
An output circuit for holding an output residual voltage higher than the voltage of the constant voltage circuit, the output circuit being driven by the output of the constant voltage circuit, First for adjusting bias current for adjusting current
And a first diode connected between the input terminal of the constant voltage circuit and the collector of the first transistor for adjusting the bias current, the first bias current source Has a first terminal, a second transistor having a collector and an emitter connected to the input terminal of the constant voltage circuit, and a resistor connected between the collector and the base of the second transistor. The second bias current source has a series connection body of a third transistor and a resistor whose emitter and collector are connected between the first terminal and the constant voltage circuit, and Of the bias current source is directly supplied to the first transistor for bias current adjustment via the first diode. A DC two-wire sensor characterized by being supplied. 2. A DC two-wire sensor in which a load and a DC power supply are connected in series between the first and second terminals, and a switching operation is performed by opening and closing between the first and second terminals. A sensor circuit section that outputs a signal; a constant voltage circuit that supplies a constant voltage to the sensor circuit section; a first bias current source that supplies a bias current to the constant voltage circuit when the output of the sensor circuit section is off; A second bias current source that supplies a bias current to the constant voltage circuit when the output of the sensor circuit unit is on, a switching unit that switches between the bias current sources according to the output of the sensor circuit unit, and an output of the sensor circuit unit. The first and second
An output circuit for holding an output residual voltage higher than the voltage of the constant voltage circuit, the first bias current source having a switching element for opening and closing the terminals of the constant voltage circuit. A second transistor having a collector and an emitter connected to an input terminal of the voltage circuit, and a resistor connected between a collector and a base of the second transistor; and the output circuit having the constant voltage. The first for bias current adjustment driven by the output of the circuit and adjusting the bias current
Transistor, a first diode connected between the input terminal of the constant voltage circuit and the collector of the bias current adjusting first transistor, and a second diode forming the first bias current source. A second diode connected in series between the base end of the transistor and the collector of the first transistor for adjusting bias current, and the second bias current source, A third transistor having an emitter and a collector connected between the first terminal and the constant voltage circuit, and a series connection body of a resistor, and a surplus current of the first bias current source Third
DC two-wire sensor, characterized in that the surplus current of the second bias current source is supplied to the first transistor for adjusting the bias current via the first diode via the diode. . 3. A negative feedback transistor, which is turned on when the output of the sensor circuit section is turned on to suppress a sudden change in the inflow current of the second bias current source. The DC two-wire sensor described in 2. 4. The constant voltage circuit comprises a plurality of diodes connected in series.
DC two-wire sensor described.