JP2000205635A - Communication circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a communication circuit in which a switching element of low breakdown strength can be employed. SOLUTION: A communication circuit applicable to an arrangement for conducting communication between first and second units 1, 2 connected with a first line L1, respectively, comprises a voltage limit circuit 11 delivering a voltage output having a peak limited lower than that of a voltage appearing on a second line L2 with reference to the potential of the first line L1, a switch element Q1 provided in the first unit 1 in order to switch the connection, and an element D7 for detecting current wherein the switch element Q1 and the detecting element D are connected in series between the output 111 of the voltage limit circuit 11 and the first line L1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication circuit for performing communication by using one line of a commercial power supply and one communication line. The present invention relates to a communication circuit using a limited voltage output lower than a maximum value of a voltage as an operation power supply.

[0002]

2. Description of the Related Art In an air conditioner separated into an indoor unit and an outdoor unit, it is necessary to perform communication between the indoor unit and the outdoor unit. For this reason, the prior art of providing one communication line between the indoor unit and the outdoor unit to which the commercial power is led and performing communication between the indoor unit and the outdoor unit is disclosed in Japanese Patent Publication No. 1-57264.
No. has been proposed. That is, in this technology, a thyristor provided in the indoor unit and a light emitting diode provided on the outdoor unit side are connected to a series circuit obtained by connecting the communication line to one line of a commercial power supply. Connected to the other line. Therefore, the on / off state of the thyristor is detected as the presence or absence of a current flowing through the light emitting diode of the outdoor unit. Therefore, when the indoor unit turns on / off the thyristor in accordance with the transmission data, the transmission data is detected as blinking of the light emitting diode in the outdoor unit (referred to as a first related art).

In the prior art proposed as Japanese Patent Publication No. 7-96948, a series circuit in which a phototriac and a bidirectional light emitting diode are connected in series is provided in each of an indoor unit and an outdoor unit. This series circuit is connected between a pair of lines of a commercial power supply. The connection point between the phototriac and the light emitting diode on the indoor unit side and the connection point between the phototriac and the light emitting diode on the outdoor unit side are connected to each other by a communication line. Therefore, in any cycle of the commercial power supply, data can be sent from any side to the other side (this is referred to as a second conventional technique).

However, the thyristor used in the first prior art and the phototriac used in the second prior art have a more complicated element configuration than a phototransistor. For this reason, the price of a thyristor or a phototriac is an expensive element compared to a phototransistor. For this reason, as shown in FIG. 3, a conventional technique using a phototransistor which is an inexpensive element has been proposed.

That is, in this technique, the photocouplers 14 and 15 are provided on the indoor unit 1 side, and the photocouplers 24 and 25 are provided on the outdoor unit 2 side. The phototransistor Q1 of the photocoupler 14, the light emitting diode D5 of the photocoupler 15, the phototransistor Q5 of the photocoupler 24, and the light emitting diode D7 of the photocoupler 25 are connected between a pair of lines L1 and L2 of the commercial power supply. Connected in series. Therefore, when the phototransistor Q5 is set to the on state, the on / off of the phototransistor Q1 is detected by the light emitting diode D7. When the phototransistor Q1 is set to the on state, the on / off of the phototransistor Q5 is detected by the light emitting diode D5. That is, transmission of data from the indoor unit 1 to the outdoor unit 2 and transmission of data from the outdoor unit 2 to the indoor unit 1 are possible. Do).

[0006]

However, in the case where the above configuration is used, the following problems have occurred. That is, when data is transmitted from the indoor unit 1 to the outdoor unit 2, the phototransistor Q5 is set to the ON state. In this state, the phototransistor Q1
Will be turned on and off according to the data. On the other hand, a commercial power supply voltage is applied to a series circuit including the phototransistor Q1, the light emitting diode D5, the phototransistor Q5, and the light emitting diode D7. Therefore, when the phototransistor Q1 is turned off, a voltage equal to the voltage of the commercial power supply (approximately 140 V at the maximum) is applied between the collector and the emitter of the phototransistor Q1. For this reason, the photocoupler 14
The withstand voltage between the collector and the emitter of the phototransistor Q1 is, for example, 200V or 300V.
An extremely high breakdown voltage element had to be used. For this reason, the price of the photocoupler 14 has been high. The same applies to the photocoupler 24,
Since a device with a high withstand voltage is required, it has been expensive.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a serial circuit in which a switch element for transmission and a detection element for reception are connected in series. It is an object of the present invention to provide a communication circuit which can use a switch element having a low withstand voltage by setting the maximum value of the applied voltage to be lower than the maximum value of the voltage of the commercial power supply.

Another object of the present invention is to simplify the configuration of a voltage limiting circuit for lowering the maximum value of the voltage by using a Zener diode to limit the maximum value of the voltage. It is an object of the present invention to provide a communication circuit.

Further, the object of the invention according to claim 3 is, in addition to the above-mentioned object, to be achieved even when a voltage drop occurs in a line in which a path for a commercial power supply and a path for a communication signal are shared. It is an object of the present invention to provide a communication circuit capable of preventing a current caused by a reduced voltage drop from flowing through a signal path.

[0010]

According to a first aspect of the present invention, there is provided a communication circuit, wherein one line of a commercial power supply is a first line, and the other line of the commercial power supply is a second line. When a line is used, the present invention is applied to a communication circuit for performing communication between a first device to which a first line is connected and a second device to which the first line is connected. A voltage limiting circuit for sending a limited voltage output in which the highest value of the voltage is lower than the highest value of the voltage generated in the second line, and a connection provided in the first device for opening and closing the connection. A switch element, provided in the second device,
A detection element for detecting the presence or absence of a current; and the switch element and the detection element are connected in series between an output of the voltage limiting circuit and a first line. That is, the maximum value of the voltage applied to the series circuit including the switch element and the detection element is lower than the maximum value of the voltage generated in the second line. Therefore, when the switch element is turned off, the maximum value of the voltage applied to the switch element becomes a low value.

In a communication circuit according to a second aspect of the present invention, in addition to the above configuration, the voltage limiting circuit further comprises a resistor having one terminal connected to the second line and a resistor connected to the other terminal of the resistor. A Zener diode connected between the first line and the first line, and the limited voltage output is taken out from the other terminal of the resistor. That is, with one resistor and one Zener diode, it is possible to obtain a limited voltage output in which the maximum value of the voltage is equal to the Zener voltage.

According to a third aspect of the present invention, in addition to the above configuration, the communication circuit is applied to a communication circuit in which a voltage drop occurs in a first line from a first device to a second device. The Zener diode is provided with a diode for preventing a current from flowing from the anode to the cathode in the Zener diode. That is, when the voltage drop generated in the first line is regarded as a voltage source, if there is no diode, a current flows from the anode to the cathode of the Zener diode. Form a current path for the voltage source. However, a diode that prevents a current from flowing from the anode to the cathode of the Zener diode blocks the current path.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an electrical connection of an embodiment of a communication circuit according to the present invention. Blocks and elements having the same configuration or the same functions as those of the prior art shown in FIG. The same reference numerals as in FIG.

In the present embodiment, bidirectional communication is performed between an indoor unit (first device) and an outdoor unit (second device) 2 constituting an air conditioner. This is a configuration for performing communication. Therefore, the indoor unit 1 and the outdoor unit 2
And the first line, which is one line of the commercial power supply,
Is connected, and a second line L2, which is the other line of the commercial power supply, is connected. Also,
One communication line L3 is provided between the indoor unit 1 and the outdoor unit 2.
Is provided. In the following, description will be made assuming that the first line L1 is a line indicating the reference (0 V) of the potential.

The indoor unit 1 includes a voltage limiting circuit 11, an indoor mechanism unit 12, an indoor control unit 13, photocouplers 14, 15,
Further, an element serving as a peripheral circuit for the photocouplers 14 and 15 is provided. The outdoor unit 2 includes an outdoor mechanism unit 22, an outdoor control unit 23, photocouplers 24 and 25,
Further, an element serving as a peripheral circuit for the photocouplers 24 and 25 is provided.

The indoor control section 13 is mainly composed of a microcomputer and is a block for controlling the main operation of the indoor unit 1. Therefore, the operation of the indoor mechanism 12 is controlled. Also, the photocouplers 14 and 15
Is used to communicate with the outdoor controller 23. The indoor mechanism unit 12 includes a blower fan that blows air into the room, a fan motor that drives the blower fan, and the like.
It is a block composed of various mechanical parts.

The outdoor control section 23 is mainly composed of a microcomputer and is a block for controlling the main operation of the outdoor unit 2. Therefore, the operation of the outdoor mechanism section 22 is controlled. Also, photocouplers 24 and 25
Is used to communicate with the indoor control unit 13. The outdoor mechanism section 22 is a block including various mechanical components such as a compressor for compressing the refrigerant and a four-way valve for switching the refrigerant path.

The voltage limiting circuit 11 to which the first line L1 and the second line L2 are connected has a maximum voltage value of:
The block that sends out a limited voltage output lower than the highest value of the voltage generated in the second line L2 from the output 111. For this purpose, a resistor R1, diodes D1 and D3, and a zener diode D2 are provided. In the present embodiment, the Zener voltage of the Zener diode D2 is about 30 V (the reason will be described later).

Specifically, one terminal of the resistor R1 is connected to the second line L2, and the Zener diode D2
Is connected to the other terminal of the resistor R1 via a diode D1. The anode of the Zener diode D2 is connected to the first line L1 via a diode D3 for preventing a forward current (current flowing from the anode to the cathode) from flowing through the Zener diode D2.
It is connected to the. Therefore, the voltage limiting circuit 11 sends out the voltage only when the second line L2 is positive, and sets the maximum value of the sending out voltage to be equal to the Zener voltage of the Zener diode D2.

The connection order of the resistor R1 and the diode D1 can be changed. Similarly, the connection order of the Zener diode D2 and the diode D3 can be changed.

The collector of the phototransistor Q1 provided in the photocoupler 14 is connected to the output 1 of the voltage limiting circuit 11.
11, the emitter of the phototransistor Q1 is connected to the anode of the light emitting diode D5 of the photocoupler 15. The cathode of the light emitting diode D5 is connected to the collector of the phototransistor Q5 of the photocoupler 24 via the communication line L3.
Further, the emitter of the phototransistor Q5 is connected to the anode of the light emitting diode D7 of the photocoupler 25,
The cathode of the light emitting diode D7 is connected to the first line L1.

That is, the phototransistor Q1 is an element for transmitting data from the indoor unit 1 side to the outdoor unit 2 side, and is an element corresponding to the switch element described in the claims. The light emitting diode D5 is an element for receiving data transmitted from the outdoor unit 2 side. Further, the phototransistor Q5 is an element for transmitting data from the outdoor unit 2 side to the indoor unit 1 side. The light emitting diode D7 is an element that receives data transmitted from the indoor unit 1 side. That is, the light emitting diode D7 is a detecting element described in the claims, and detects the presence or absence of a current in the communication line L3.

The resistors R3 to R5 and the transistor Q
Reference numeral 3 denotes an element for driving the light emitting diode D4. That is, the resistor R3 limits the current of the light emitting diode D4, and the resistor R4 limits the base current of the transistor Q3. The resistor R5 is connected to the transistor Q3
To prevent the base from being opened. Therefore, when the indoor control unit 13 sends the H level to the terminal of the resistor R4, the phototransistor Q1 is turned on.

The resistor R6 connected between the emitter of the phototransistor Q2 and the ground level is the load resistance of the phototransistor Q2. Therefore, when a current flows through the light emitting diode D5, an H level is transmitted from the emitter of the phototransistor Q2.

The resistors R8 to R10 and the transistor Q7 are elements for driving the light emitting diode D6. That is, the resistor R8 is connected to the light emitting diode D6.
The resistor R9 limits the base current of the transistor Q7. Further, the resistor R10 prevents the base of the transistor Q7 from being opened. For this reason,
When the outdoor control unit 23 sends the H level to the terminal of the resistor R9, the phototransistor Q5 turns on.

The resistor R11 connected between the emitter of the phototransistor Q6 and the ground level is the load resistance of the phototransistor Q6. Therefore, when a current flows through the light emitting diode D7, the H level is transmitted from the emitter of the phototransistor Q6.

A resistor R2 connected between the collector of the phototransistor Q1 and the cathode of the light emitting diode D5
Indicates that the reverse voltage applied to the light emitting diode D5 is 0 V
Element. That is, when the second line L2 is negative, no current flows through the communication line L3, and the voltage between the terminals of the resistor R2 becomes zero.
V. The same holds true for the resistor R7 connected between the collector of the phototransistor Q5 and the cathode of the light emitting diode D7, which is an element for setting the reverse voltage applied to the light emitting diode D7 to 0V. .
Therefore, the reverse voltage (the maximum value is about 140 V) appears between the cathode and the anode of the diode D1.

When the compressor of the outdoor mechanism 22 operates, a large current (for example, about 15 A) flows through the first line L1 and the second line L2. Therefore, a line connecting the cathode of the diode D3 and the first line L1 (P5) and a line connecting the cathode of the light emitting diode D7 and the first line L1 (P6). A portion where the line and the signal line of the communication circuit are shared) has a voltage drop corresponding to the resistance of the intervening line. The noise source 3 is a block for equivalently indicating a voltage drop generated between the connection point P5 and the connection point P6. In the present embodiment, it is assumed that the noise source 3 generates a voltage having a peak value of 10 V in the worst case.

As described above, the voltage limiting circuit 11
Restricts the voltage of the output 111 so that the maximum value is 30V. Therefore, when the phototransistor Q5 is set to the on state, when the phototransistor Q1 is turned off, the maximum value of the collector-emitter voltage of the phototransistor Q1 is limited to 30V.
This is the same for the phototransistor Q5. Therefore, the phototransistors Q1 and Q5 only need to be devices having a withstand voltage between the collector and the emitter of 30 V or more. Therefore, when safety is expected, 5
It is possible to use an element having a low withstand voltage such as 0 V.

FIG. 2 is an explanatory diagram showing voltage waveforms at main points in the embodiment. The operation of the embodiment will be described with reference to FIG.

A signal waveform 31 shown in FIG. 2 shows a voltage waveform of the second line L2 (a voltage waveform of a commercial power supply).
The highest value is about 140V. Now, it is assumed that at least one of the phototransistors Q1 and Q5 is off and no current flows through the communication line L3 (ignoring the currents of the resistors R2 and R7). At this time, the voltage of the output 111 is, as shown by the signal waveform 32, that the voltage of the second line L2 is 3
In the period t1 exceeding 0V, the voltage is limited to 30V (indicated by V1).

Now, since the compressor of the outdoor mechanism section 22 is not operating, the outdoor unit 2 is connected via the first line L1.
Is small, and the noise level generated by the noise source 3 is near 0 V (indicated by 34). At this time, the voltage waveform of the output 111 viewed from the connection point P6 becomes a waveform 35 equal to the voltage waveform 32 of the output 111 viewed from the connection point P5. Therefore, the phototransistor Q
1, a voltage maintained at 30 V is applied to a signal path including the light emitting diode D5, the phototransistor Q5, and the light emitting diode D7 during the period t1.

Therefore, when the phototransistor Q5 is turned on and the phototransistor Q1 is turned on and off, or when the phototransistor Q1 is turned on and the phototransistor Q5 is turned on and off, the voltage of the output 111 becomes as indicated by 36. Change.
Therefore, the noise margin at this time is about 30 V,
Communication is performed in a state of extremely high noise resistance.

Now, since the compressor of the outdoor mechanism section 22 is operated at the maximum output and the current flowing through the outdoor unit 2 via the first line L1 is large, the noise generated by the noise source 3 (dashed line) 33), but the peak value is 1
It is assumed that the voltage reaches 0V. At this time, the voltage waveform of the output 111 as viewed from the connection point P6 is the output 1 as viewed from the connection point P5.
Waveform 3 showing the difference between the voltage waveform 32 of 11 and the noise 33
It becomes 7. That is, the voltage waveform applied to the signal path including the phototransistor Q1, the light-emitting diode D5, the phototransistor Q5, and the light-emitting diode D7 has a waveform 37 that decreases to 20 V (indicated by V2) when it is minimum.

Therefore, when the phototransistor Q5 is turned on and the phototransistor Q1 is turned on and off, or when the phototransistor Q1 is turned on and the phototransistor Q5 is turned on and off, the voltage of the output 111 becomes as shown at 38. Change.
Therefore, the noise margin at this time is about 20 V as a worst value. That is, the noise margin is lower than when the noise level of the noise source 3 is 0V. However, since the impedance of the signal path including the communication line L3 is low, the noise margin of 20 V is a value that does not hinder communication in practical use.

As described above, when the maximum value of the voltage of the limited voltage output sent from the voltage limiting circuit 11 is reduced, the withstand voltage required for the phototransistors Q1 and Q5 can be reduced. On the other hand, when increasing the maximum value of the voltage of the limited voltage output, the noise margin can be increased. For this reason, in the present embodiment, the maximum value of the limited voltage output voltage is set to 30 V as a value that satisfies both requirements. In addition, the maximum value of the voltage of the limited voltage output can be set to another value.

The operation of the diode D3 will be described below. When the second line L2 is negative,
The noise source 3 generates noise in which the connection point P5 side is positive and the connection point P6 side is negative. Therefore,
When there is no diode D3, the Zener diode D
2. A current path including the phototransistor Q1, the light emitting diode D5, the phototransistor Q5, and the light emitting diode D7 is formed. Therefore, the phototransistor Q
If at least one of Q1 and Q5 is not maintained in the off state, the voltage generated by the noise source 3 causes a problem that a current flows through the path (in a standby state of waiting for transmission from the other party, the phototransistors Q1 and Q5
Are set to the ON state). However, when the diode D3 is provided, the above-described path is not formed. Accordingly, when the second line L2 is negative, it is not necessary to set at least one of the phototransistors Q1 and Q5 to OFF, and the indoor control unit 1
3 and the control method of the outdoor control unit 23 can be simplified.

Note that the present invention is not limited to the above embodiment, and a case has been described in which communication is enabled only when the second line L2 is positive with respect to the first line L1. The present invention can be similarly applied to a configuration in which communication is enabled both when the second line L2 becomes positive and when the second line L2 becomes negative with respect to the first line L1. I have.

The case where the switching elements are the phototransistors Q1 and Q5 has been described.
As other elements, for example, a photothyristor, a phototriac, or the like can be used.

[0040]

According to the communication circuit according to the first aspect of the present invention,
Applying one of the commercial power supplies as a first line and the other as a second line to a communication circuit for performing communication between a first device and a second device each connected to the first line, With the first line as the potential reference, the highest voltage is
A voltage limiting circuit for sending a limited voltage output having a voltage lower than the highest value of the voltage generated in the line, a switch element provided in the first device for opening and closing the connection, and a switch device provided in the second device for controlling the current. A detection element for detecting the presence / absence of the switching element, wherein the switch element and the detection element are connected in series between an output of the voltage limiting circuit and a first line. Therefore, the maximum value of the voltage applied to the series circuit including the switch element and the detection element is lower than the maximum value of the voltage of the second line. For this reason, when the switch element is turned off, the maximum value of the voltage applied to the switch element becomes a low value, so that a switch element having a low withstand voltage can be used.

According to a second aspect of the present invention, in the communication circuit, the voltage limiting circuit includes a resistor having one terminal connected to the second line, and a resistor connected to the other terminal of the resistor and the first line. A Zener diode connected between the resistors, and configured to extract the limited voltage output from the other terminal of the resistor. Therefore, with one resistor and one Zener diode, it is possible to obtain a limited voltage output in which the maximum value of the voltage is equal to the Zener voltage. For this reason, it is possible to simplify the configuration of the voltage limiting circuit that lowers the maximum value of the voltage.

A communication circuit according to a third aspect of the present invention is applied to a communication circuit in which a voltage drop occurs in a first line from a first device to a second device, wherein the Zener diode has an anode to a cathode. In this method, a diode for preventing a current from flowing is provided. Therefore, even when the voltage drop generated in the first line is regarded as a voltage source, the series circuit including the switch element and the detection element does not form a current path due to the blocking action of the diode. Therefore, even when a voltage drop occurs in a line where the path for the commercial power supply and the path for the communication signal are shared, the current caused by the generated voltage drop is prevented from flowing through the signal path. Is possible.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an electrical connection of a communication circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing voltage waveforms of main parts of the embodiment.

FIG. 3 is a circuit diagram showing a conventional electrical connection.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Indoor unit (1st apparatus) 2 Outdoor unit (2nd apparatus) 3 Noise source equivalently showing the voltage drop generated in the 1st line 11 Voltage limiting circuit 111 Output of voltage limiting circuit D2 Zener diode D3 Diode for preventing forward current of Zener diode D7 Detection element L1 First line L2 Second line L3 Communication line Q1 Switch element R1 Resistance

Claims (3)

[Claims] When one line of a commercial power supply is a first line and the other line of the commercial power supply is a second line, a first device to which the first line is connected, In a communication circuit that communicates with a second device to which a line is connected, when the first line is regarded as a reference of potential, the highest value of the voltage is lower than the highest value of the voltage generated in the second line. A voltage limiting circuit for sending a limited voltage output as a voltage, a switch element provided in the first device for opening and closing a connection, and a detecting element provided in the second device for detecting the presence or absence of a current, A communication circuit, wherein the switch element and the detection element are connected in series between an output of the voltage limiting circuit and a first line. 2. The voltage limiting circuit includes: a resistor having one terminal connected to a second line; and a Zener diode connected between the other terminal of the resistor and a first line. 2. The communication circuit according to claim 1, wherein the limited voltage output is taken out from the other terminal of the resistor. 3. A communication circuit in which a voltage drop occurs in a first line from a first device to a second device, wherein a diode for preventing a current from flowing from an anode to a cathode of the zener diode is provided. 3. The communication circuit according to claim 2, wherein: