JPH10253668A - Current-voltage converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption by detecting potential difference between both ends of a resistance through which a current signal flows, connecting an analog switch to both ends of the resistance to be opened in the current- voltage conversion and closed in the other cases. SOLUTION: A current signal 100c is sent to a resistance 1c and the potential between both sends thereof is inputted to a difference amplifier 2b and simultaneously controlled by a control signal 102 and a transistor 7. The output of the difference amplifier 2b becomes an output signal 101b through an amplifier 3b and an A/D converter 4b. The control signal 102 turns on the transistor 7 in the normal H level to send the current signal 100c to the resistance 1c and the transistor 7. The control signal 102 is set to the L level in synchronization with the conversion timing of the A/D converter 4b to turn off the transistor 7 and sent the current signal 100c only to the resistance 1c so that the potential difference caused by the voltage drop is subjected to A/D conversion to enable the current-voltage conversion. Thus, the current signal 100c is diverted in the case except for the conversion, the power consumption can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-voltage conversion circuit for converting a current signal of 4 to 20 mA or the like into a voltage signal, and more particularly to a current-voltage conversion circuit capable of reducing power consumption.

[0002]

2. Description of the Related Art Generally, a current output of a converter or the like is 4 to 20 m.
When measuring this current value, the current output was once converted to a voltage value and taken into a control circuit or the like by an A / D converter or the like.

FIG. 5 is a configuration block diagram showing an example of such a conventional current-voltage conversion circuit. In FIG. 5, 1 is a resistor, 2 is a differential amplifier, 3 is an amplifier, 4 is an A / D converter, 100 is a current signal from a converter or the like, and 101 is an output signal.

A current signal 100 is input to one end of a resistor 1 and one input terminal of a differential amplifier 2. A current signal 100 flowing through the resistor 1 is input to the other input terminal of the differential amplifier 2 and a converter. Etc. (not shown).

The output of the differential amplifier 2 is supplied to A
The output of the A / D converter 4 is connected as an output signal 101 to a higher-level control circuit or the like (not shown).

Now, the operation of the conventional example shown in FIG. 5 will be described. When the current signal 100 flows through the resistor 1, the resistor 1
, A potential difference occurs due to the voltage drop.

The differential amplifier 2 detects a potential difference between both ends of the resistor 1 and outputs it to the amplifier 3 as a voltage signal. The amplifier 3 appropriately amplifies the voltage signal so as to match the input range of the A / D converter 4 at the subsequent stage and supplies the voltage signal to the A / D converter 4.

The A / D converter 4 converts an output signal from the amplifier 3 into a digital signal and supplies it to a higher-level control circuit.

As a result, the current signal can be converted into a voltage signal by detecting the potential difference generated between both ends of the resistor 1 with the differential amplifier 2.

FIG. 6 is a block diagram showing an example of a conventional current-voltage conversion circuit having a plurality of channels.

In FIG. 6, 1a and 1b are resistors, 2a is a differential amplifier, 3a is an amplifier, 4a is an A / D converter, 5a
a, 5b, 6a and 6b are switch circuits, 100a and 100b are current signals from a converter or the like, and 101a is an output signal.

The current signal 100a is input to one end of the resistor 1a and one end of the switch circuit 5a, and the current signal 100a flowing through the resistor 1a is input to one end of the switch circuit 6a and to a converter or the like (not shown). Go back.

Similarly, the current signal 100b is input to one end of the resistor 1b and one end of the switch circuit 5b, and the current signal 100b flowing through the resistor 1b is input to one end of the switch circuit 6b and is connected to another converter (see FIG. 1). (Not shown).

The other end of the switch circuit 5a is connected to a differential amplifier 2a.
The other end of the switch circuit 6a is connected to the other input terminal of the differential amplifier 2a and the other end of the switch circuit 6b.

The output of the differential amplifier 2a is connected to an A / D converter 4a via an amplifier 3a, and the output of the A / D converter 4a is output as an output signal 101a to a higher-level control circuit or the like (not shown). Connected.

Here, the operation of the conventional example shown in FIG. 6 will be described. However, the basic operation is the same as that of the conventional example shown in FIG.

When converting the current signal 100a, the switch circuits 5a and 6a are turned "on" and the switch circuits 5b and 6b are turned "off", and the potential difference generated across the resistor 1a is detected by the differential amplifier 2a.

When converting the current signal 100b, the switch circuits 5a and 6a are turned "off" and the switch circuits 5b and 6b are turned "on" to detect a potential difference generated between both ends of the resistor 1b by the differential amplifier 2a. .

As a result, the switch circuits 5a, 5b, 6a
And 6b, it is possible to sequentially convert the current signals 100a and 100b into voltage signals. That is, it becomes possible to convert current signals of a plurality of channels into voltage signals.

[0020]

However, when the current signal is 4
When the input current value is "20 mA", "0.1 W" is consumed by this resistor when the input current value is "20 mA". become.

In particular, in a multi-channel current-voltage conversion circuit as shown in FIG. 6, the power consumption increases in accordance with the number of channels. For example, the power consumption “P” in the case of a 10-channel current-voltage conversion circuit is as follows: P = 0.1 W × 10 = 1.0 W (1)

There is a problem that the operating temperature range of the current-voltage conversion circuit is restricted because heat is generated by such power consumption and the temperature of the current-voltage conversion circuit is raised. Therefore, an object of the present invention is to realize a current-voltage conversion circuit capable of reducing power consumption.

[0023]

According to a first aspect of the present invention, there is provided a current-to-voltage conversion circuit for converting a current signal into a voltage signal. A resistor that generates a potential difference, a differential amplifier that detects the potential difference as a voltage signal, and an analog switch that is connected to both ends of the resistor and that is open during current-voltage conversion and closed otherwise. It is a feature.

According to a second aspect of the present invention, there is provided a current-to-voltage conversion circuit for converting a current signal into a voltage signal. A plurality of resistors, a differential amplifier that detects a potential difference as a voltage signal, a plurality of switch circuits that supply one of the plurality of potential differences to the differential amplifier, and a plurality of switches connected to both ends of the plurality of resistors. And an analog switch that is open or closed when the plurality of switch circuits connected to the resistor are closed or open.

In order to achieve the above object, a third aspect of the present invention is characterized in that in the first and second aspects of the present invention, the analog switch is a transistor.

In order to achieve such an object, a fourth aspect of the present invention is characterized in that in the first and second aspects of the present invention, the analog switch is a photocoupler.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration block diagram showing one embodiment of a current-voltage conversion circuit according to the present invention.

In FIG. 1, 1c is a resistor, 2b is a differential amplifier, 3b is an amplifier, 4b is an A / D converter, 7 is a transistor which is an analog switch, 100c is a current signal from a converter or the like, and 101b is an output signal. , 102 are control signals.

The current signal 100c is input to one end of the resistor 1c, one input terminal of the differential amplifier 2b and the collector of the transistor 7, and the current signal 100c flowing through the resistor 1c is input to the other input terminal of the differential amplifier 2b and the transistor. 7 and return to a converter or the like (not shown). Further, the control signal 102 is input to the base of the transistor 7.

The output of the differential amplifier 2b is connected to the A / D converter 4b via the amplifier 3b, and the output of the A / D converter 4b is output as an output signal 101b to a higher-level control circuit or the like (not shown). Connected

Here, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a timing chart showing the control signal 102 and the timing of A / D conversion. 2A shows the control signal 102, and FIG. 2B shows the A / D conversion timing.

As shown by "A" in FIG.
Is normally at a high level, so that transistor 7 has "o"
n ”, and the current signal 100c flows to both the resistor 1c and the transistor 7.

The control signal 102 goes low as shown at "c" in FIG. 2 in synchronization with the conversion timing of the A / D converter 4b shown at "b" in FIG. As a result, the transistor 7 becomes “off”, and the current signal 100 c becomes the resistance 1 c
Will flow only to

Therefore, since only the potential difference caused by the voltage drop at the resistor 1c is A / D converted, the same current-voltage conversion as in the conventional example is performed.

Consider power consumption. The conditions are the same as in the conventional example, and the resistance 1c is a resistance of “250Ω” and the current signal 100c is “20 mA”.

When the transistor 7 is "off", all the current signal 100c flows through the resistor 1c, so that the power consumption becomes "0.1 W" as in the conventional example.

On the other hand, when the transistor 7 is "on", the resistance value of the current flowing through the resistor 1c is "250 Ω". Therefore, when "Vce" is set to "1 V", 1 V / 250 Ω = 4 mA (2) Become.

Since the current signal 100c is set to "20 mA", a current of "16 mA" flows through the transistor 7.

Therefore, the power consumption "P1" and "P2" of the resistor 1c and the transistor 7 are set such that "Vce" becomes "1".
V ”, P1 = 1V × 4mA = 0.004W (3) P2 = 1V × 16mA = 0.016W (4)

That is, the power consumption "P3" when the transistor 7 is "on" is as follows: P3 = 0.004W + 0.016W = 0.02W (5)

Assuming that the ratio between the high level and the low level indicated by "A" and "C" in FIG. 2 is "1/2", the average power consumption "P4" of the current-voltage conversion circuit is P4 = {( 0.004W + 0.016W) + 0.1W} /2=0.06W (6)

The power consumption of the conventional example shown in FIG.
W ", which means that the power consumption has been reduced by" 40% ".

As a result, the transistor 7 is provided in parallel with the resistor 1c, and the transistor 7 is set to "o" at the time other than the current-voltage conversion.
By shunting the current signal 100c to n ″, power consumption can be reduced.

Further, by reducing the average power consumption of the current-voltage conversion circuit, the temperature rise is suppressed, and the operating temperature range of the current-voltage conversion circuit can be expanded.

FIG. 3 is a block diagram showing an embodiment of a current-voltage conversion circuit having a plurality of channels.

In FIG. 3, 1d and 1e are resistors, 2c is a differential amplifier, 3c is an amplifier, 4c is an A / D converter, and 8a
And 8b are photocouplers, 9a, 9b, 10a and 10
b is a switch circuit, 100d and 100e are current signals,
101c is an output signal, and 103 and 104 are control signals for the photocouplers 8a and 8b.

The current signal 100d is input to one end of the resistor 1d, the collector of the phototransistor forming the photocoupler 8a, and one end of the switch circuit 9a. It is input to one end of the emitter and switch circuit 10a and returns to a converter or the like (not shown).

Similarly, the current signal 100e is inputted to one end of the resistor 1e, the collector of the phototransistor constituting the photocoupler 8b and one end of the switch circuit 9b, and the current signal 100e flowing through the resistor 1e constitutes the photocoupler 8b. The light is input to the emitter of the phototransistor and one end of the switch circuit 10b, and returns to another converter (not shown).

Control signals 103 and 104 are connected to the anodes of the photodiodes constituting the photocouplers 8a and 8b, respectively.
Are individually grounded.

The other end of the switch circuit 9a is connected to a differential amplifier 2c.
The other end of the switch circuit 10a is connected to the other input terminal of the differential amplifier 2c and the other end of the switch circuit 10b.

The output of the differential amplifier 2c is connected to the A / D converter 4c via the amplifier 3c, and the output of the A / D converter 4c is output to an upper control circuit or the like (not shown) as an output signal 101c. Connected.

The operation of the embodiment shown in FIG. 3 will be described with reference to FIG. FIG. 4 is a timing chart showing the operation of the control signal and the switch circuit.

4A shows the state of the switch circuits 9a and 10a, and FIG. 4B shows the state of the switch circuits 9b and 10b.
(C) is the control signal 103, (d) is the control signal 1
04 is shown.

In FIG. 4, "a", "b", "c" and "d" are shown.
Since the control signals 103 and 104 are normally at a high level, the photocouplers 8a and 8b are turned "on", and the current signal 100d is connected to the resistor 1d and the photocoupler 8 as shown in FIG.
It flows to both phototransistors constituting a.

Similarly, the current signal 100e is connected to the resistor 1e.
And the phototransistor constituting the photocoupler 8b.

In synchronization with the "on" timing of the switch circuits 9a and 10a indicated by "e" in FIG. 4, "f" in FIG.
The control signal 103 goes low as shown in FIG. Therefore, the phototransistor constituting the photocoupler 8a is turned "off", and the current signal 100d flows only to the resistor 1d.

Similarly, the control signal 104 goes low as shown by "h" in FIG. 4 in synchronization with the "on" timing of the switch circuits 9b and 10b shown by "g" in FIG. For this reason, the phototransistor constituting the photocoupler 8b becomes "off", and the current signal 100e flows only to the resistor 1e.

Therefore, only the potential difference caused by the voltage drop at the resistors 1d and 1e is sequentially selected by the switch circuit and detected by the differential amplifier 2c, so that the current signals of a plurality of channels can be converted into voltage signals.

Consider power consumption. Similarly to the above-described conditions, the resistors 1d and 1e have a resistance of “250Ω”, and the current signals 100d and 100e have a resistance of “20 mA”.

As described above, the photocouplers 8a and 8b
Is “off”, the power consumption is “0.1 W”,
On the other hand, when the photocouplers 8a and 8b are "on", the power consumption is "0.02W".

Assuming that the number of channels is "10" and a plurality of channels are scanned in a time division manner, the time when the photocoupler is "on" and "off" is "9/10" and "9/10".
Therefore, the average power consumption “P5” of one channel of the current-voltage conversion circuit is P5 = 0.02W × 9/10 + 0.1W × 1/10 = 0.028W (7)

Accordingly, the average power consumption “P6” for the ten channels is as follows: P6 = P5 × 10 = 0.028W × 10 = 0.28W (8)

That is, as shown in the equation (1), the power consumption of the conventional example of 10 channels was "1.0 W", which means that the power consumption was reduced by "72%".

As a result, the photocouplers 8a and 8b are provided in parallel with the resistors 1d and 1e, and the switch circuits 9a and 9b are provided.
b, 10a and 10b select the potential difference between both ends of the resistor 1d or the resistor 1e, and turn on the phototransistor constituting the photocoupler connected to the resistor except when the resistor is selected to shunt the current signals 100d and 100e. Thus, power consumption can be reduced.

Although a transistor and a photocoupler have been illustrated as analog switches, other analog switches may be used.

FIG. 3 illustrates a two-channel configuration for simplicity of explanation, but is not limited to this.

Further, in the description of FIG.
The timing of "on" and "off" is set to "1/2", but the present invention is not limited to this. For example, if the "off" time of the transistor 7 is increased, the average power consumption of the current-voltage conversion circuit is reduced. It can be further reduced.

In the embodiment shown in FIG. 1 and the like, the A / D converter 4b and the amplifier 3b at the preceding stage are provided, but they are not essential components for the current-voltage conversion circuit.

[0069]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. By providing an analog switch in parallel with the resistor and turning on the analog switch "on" at times other than the current-voltage conversion to shunt the current signal, a current-voltage conversion circuit capable of reducing power consumption can be realized.

Further, since the average power consumption of the current-voltage conversion circuit is reduced, the temperature rise is suppressed, and the operating temperature range of the current-voltage conversion circuit can be expanded.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram showing one embodiment of a current-voltage conversion circuit according to the present invention.

FIG. 2 is a timing chart showing timings of a control signal and A / D conversion.

FIG. 3 is a configuration block diagram illustrating an embodiment of a current-voltage conversion circuit having a plurality of channels.

FIG. 4 is a timing chart showing the operation of a control signal and a switch circuit.

FIG. 5 is a configuration block diagram illustrating an example of a conventional current-voltage conversion circuit.

FIG. 6 is a configuration block diagram illustrating an example of a conventional current-voltage conversion circuit having a plurality of channels.

[Explanation of symbols]

1, 1a, 1b, 1c, 1d, 1e Resistance 2, 2a, 2b, 2c Differential amplifier 3, 3a, 3b, 3c Amplifier 4, 4a, 4b, 4c A / D converter 5a, 5b, 6a, 6b, 9a, 9b, 10a, 10b
Switch circuit 7 Transistor 8a, 8b Photocoupler 100, 100a, 100b, 100c, 100d, 1
00e Current signal 101, 101a, 101b, 101c Output signal 102, 103, 104 Control signal

Claims (4)

[Claims] A current-voltage conversion circuit for converting a current signal into a voltage signal; a resistor for generating a potential difference between both ends by flowing the current signal; a differential amplifier for detecting the potential difference as a voltage signal; An analog switch that is connected to both ends of the resistor and that is open during current-voltage conversion and closed otherwise. 2. A current-voltage conversion circuit for converting a current signal into a voltage signal, comprising: a plurality of resistors for generating a potential difference between both ends by flowing the plurality of current signals; and a differential for detecting the potential difference as a voltage signal. An amplifier; a plurality of switch circuits for supplying one of the plurality of potential differences to the differential amplifier; and a plurality of switch circuits connected to both ends of the plurality of resistors, respectively, and the plurality of switch circuits connected to the plurality of resistors are closed or open. A current-voltage conversion circuit, comprising: an analog switch that is opened or closed in the case of (1). 3. A current-to-voltage converter according to claim 1, wherein said analog switch is a transistor. 4. The current-voltage converter according to claim 1, wherein said analog switch is a photocoupler.