JP4451718B2 - Power supply device and power supply method - Google Patents

Description

  The present invention relates to a power supply device and a power supply method used for communication by a current loop method.

  The current loop method is a communication method for transmitting a signal according to a change in current value, and is a communication terminal device connected between transmission lines when the loop current is ON (for example, 30 mA) and OFF (for example, 2 mA). This is a communication method for transmitting a communication signal to. In this communication system, the communication signal when the loop current is turned on is called the mark signal, the loop current at that time is called the mark current, the communication signal when the loop current is turned off is called the space signal, and the loop current at that time is called the space current. (For example, refer to Patent Document 1).

  FIG. 7 is a circuit diagram showing a main part of a communication system employing a conventional current loop system. In the figure, 1 is a power supply device, L1 and L2 are transmission lines (transmission lines) connected to the power supply device 1, and a master unit 2 and a slave unit 3-1 as communication terminal devices between the transmission lines L1 and L2. ˜3-n are connected in series.

  The power supply device 1 is provided with a constant voltage source 1-1 and a constant current unit 1-2. The constant current unit 1-2 is connected between the transmission line L2 and the negative polarity side of the constant voltage source 1-1. That is, the constant current unit 1-2 is connected in series between the communication terminal device group (master unit 2 and slave units 3-1 to 3-n) between the transmission lines L1 and L2 and the constant voltage source 1-1. Has been. A load voltage VO is supplied from the power supply device 1 between the transmission lines L1 and L2.

  The constant voltage source 1-1 is a series connection circuit (terminals P1, P1) of a communication terminal device group (master unit 2 and slave units 3-1 to 3-n) between the transmission lines L1 and L2 and the constant current unit 1-2. A constant voltage (output voltage) VS is supplied between P2). The constant current unit 1-2 includes an NPN transistor Q1, resistors R1 and R2, and a Zener diode ZD1, and operates by a difference (drop voltage) VD between the output voltage VS of the constant voltage source 1-1 and the load voltage VO. Stabilize the mark current during communication.

  FIG. 8 illustrates a time chart during normal communication in this communication system. 2A is a transmission waveform of the slave unit 3, FIG. 2B is a loop current I flowing through the transmission lines L1 and L2, and FIG. 2C is supplied from the power supply 1 between the transmission lines L1 and L2. The load voltage VO, (d) of FIG. This example shows an operation example when the communication cable (transmission lines L1, L2) is short and the stray capacitance CL between the transmission lines L1, L2 is small (when the stray capacitance CL can be ignored). The influence of the stray capacitance CL will be described later.

When the handset 3 transmits a mark signal (“1” level signal), the loop current I is set to the mark current IM (30 mA), and the operation of the constant current unit 1-2 stabilizes the mark current IM. It is done. The base unit 2 detects this mark current IM and receives it as a mark signal from the handset 3. At this time, load voltage VO, when the drop voltage VD for the constant current unit 1-2 and VD _M, a VO = VS-VD _M. Hereinafter, the load voltage VO at this time is referred to as a mark voltage VO _M (VO _M = VS−VD _M ).

When the handset 3 transmits a space signal (“0” level signal), the loop current I is set to the space current IS (2 mA). The constant current unit 1-2 is designed to stabilize only the mark current IM. In order to maintain the loop current I at the mark current IM, the constant current unit 1-2 attempts to reduce the internal resistance. However, since the value of the space current IS is small, the loop current I cannot be returned to the mark current IM no matter how much the internal resistance in the constant current unit 1-2 is reduced, and eventually becomes the space current IS. . As a result, the drop voltage VD at the constant current unit 1-2 decreases and the load voltage VO increases. The base unit 2 detects this space current IS and receives it as a space signal from the handset 3. At this time, load voltage VO, when the drop voltage VD for the constant current unit 1-2 and _{VD S (VD S <VD M} ), a VO = VS-VD _S. Hereinafter, the load voltage VO at this time is referred to as a space voltage VO _S (VO _S = VS−VD _S ).

  When communication is not performed, the loop current I flowing through the transmission lines L1 and L2 is set to the mark current IM. That is, in this communication system, the mark current IM (30 mA) is set as a standby current during non-communication.

Japanese Patent Laid-Open No. 11-68856

However, the communication system described above has the following two problems.
[First problem]
For example, when the number of slave units 3 is reduced, the output voltage VS of the constant voltage source 1-1 is constant, so that the load voltage VO is reduced and the drop voltage VD at the constant current unit 1-2 is increased. For this reason, in particular, when the loop current I is the mark current IM which is set to 30 mA, the power consumption in the constant current unit 1-2 is large, and energy saving is hindered. Moreover, in order to solve the heat generation accompanying the power consumption in the constant current unit 1-2, it is necessary to take measures such as using a component with a large rating and adding a heat sink. As a result, the size of the constant current unit 1-2 is increased, which prevents the power supply device 1 from being downsized.

[Second problem]
FIG. 8 illustrates a time chart when the communication cable is short and the stray capacitance CL between the transmission lines L1 and L2 is small. In this example, when the load voltage VO increases when the loop current I is the space current IS, the charging time for the stray capacitance CL can be ignored. However, when the communication cable is long, the stray capacitance CL between the transmission lines L1 and L2 becomes large, and the charging time for the stray capacitance CL when the load voltage VO rises cannot be ignored.

  FIG. 9 illustrates a time chart when the communication cable is long. When the handset 3 transmits a space signal (point t1 shown in FIG. 9A), the loop current I is set to the space current IS (2 mA). The constant current unit 1-2 operates in the same manner as described above, and increases the load voltage VO. At this time, since the charging current for the stray capacitance CL is generated, the loop current I does not immediately become the space current IS but gradually decreases. Further, the load voltage VO does not increase immediately but gradually increases. For this reason, the timing at which the parent device 2 detects the space current IS, that is, the timing at which the space signal is received from the child device 3 is delayed (point t2 shown in FIG. 9 (d)).

  On the other hand, when the handset 3 switches the space signal to the mark signal and transmits it (point t3 shown in FIG. 9A), the loop current I is returned to the mark current IM (30 mA). In this case, since the total voltage across the slave units becomes small, the charge charged in the stray capacitance CL is quickly discharged to the slave units. As a result, the loop current I returns to the mark current IM with a slight delay. The base unit 2 detects this mark current IM and receives it as a mark signal from the handset 3 (point t4 shown in FIG. 9 (d)).

  In this way, when the communication cable is long, the waveform received by the base unit 2 is distorted due to the time difference between charging and discharging at the stray capacitance CL. As the communication cable becomes longer, the stray capacitance CL increases and the received waveform distortion also increases. As shown in FIG. 9D, when the reception waveform of the space signal is ½ or less (½ · BT or less) of the transmission waveform, it cannot be received correctly and a communication error occurs.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a power supply apparatus and a power supply method capable of achieving both energy saving and space saving and improvement in communication reliability. Is to provide.

  In order to achieve such an object, the first invention (the invention according to claim 1) has a first current value (mark signal) and a second current value (space signal) smaller than the first current value. In a power supply apparatus that supplies a voltage between transmission lines connected to a group of communication terminal apparatuses that are used and communicate by a current loop method, a constant voltage source that outputs a constant voltage, and a communication terminal between the constant voltage source and the transmission line A constant current unit that is connected to the device group and stabilizes the current flowing through the transmission line at the first current value at the time of communication using the first current value; and the communication terminal device group between the transmission lines. The output voltage from the constant voltage source to the series connection circuit with the current source is adjusted so that the drop voltage at the constant current unit is a predetermined constant value, and the adjustment is performed immediately before the adjustment stop when the adjustment is stopped. A voltage adjustment unit for holding the output voltage; When communicating using the second current value is obtained by providing a voltage adjustment stop for stopping the adjustment of the output voltage from the constant voltage source by the voltage adjusting unit.

According to the present invention, to the serial connection circuit of the communication terminal device group between the transmission lines and the constant current source so that the drop voltage (VD) at the constant current portion becomes a predetermined constant value (VD _MS ). The output voltage (VS) from the constant voltage source is adjusted. As a result, it is possible to prevent an increase in power consumption in the constant current unit when the number of communication terminal devices decreases, and to realize energy saving and space saving. That is, in this invention, when the number of communication terminal devices decreases, the load voltage (VO) between the transmission lines decreases, and the drop voltage VD at the constant current portion increases. Here, when the drop voltage VD for communication of using a mark current and VD _M, the elevated voltage drop VD _M is applied to the voltage regulator. Voltage adjusting unit so as to drop voltage VD _M a constant value VD _MS, lowering the output voltage VS from the constant voltage source. Thus, the difference between the output voltage VS and the load voltage VO decreases, the increase in the drop voltage VD _M in the constant current portion is suppressed, the increase in power consumption in the constant current portion is prevented.

In the present invention, the constant current unit has a larger current (mark current) flowing through the transmission line during communication using the mark signal than a current (space current) during communication using the space signal (for example, 30 mA). When the communication signal is switched from the mark signal to the space signal, the current (space current) flowing through the transmission line is set to a value (for example, 2 mA) smaller than the mark current. At this time, the constant current unit tries to maintain the loop current at the mark current, but cannot maintain it when the loop current is significantly reduced, and the current flowing through the transmission line eventually becomes a space current. As a result, the drop voltage VD of the constant current portion (VD _S) is reduced.

Here, assuming that the voltage adjustment stop is not provided, so that the voltage adjusting unit to the drop voltage VD _S a constant value VD _MS, increase the output voltage VS from the constant voltage source. At this time, the difference between the predetermined value VD _MS and drop voltage VD _S is large, the output voltage VS will be greatly increased. Therefore, the load voltage VO between the transmission line is large increases, the difference between the mark voltage VO _M and the space voltage VO _S becomes excessive, the incidence of communication errors caused by charging and discharging of the stray capacitance between the transmission line is high .

On the other hand, in the present invention, a voltage adjustment stop unit is provided, and the adjustment of the output voltage VS from the constant voltage source is stopped during communication using the space signal. At this time, the voltage adjustment unit holds the adjusted voltage immediately before the adjustment is stopped. For this reason, the output voltage VS to the series connection circuit of the communication terminal device group between the transmission lines and the constant current source is kept at the time of communication using the mark signal. As a result, the load voltage VO between the transmission lines is increased by the drop (ΔVD) of the drop voltage VD at the constant current portion. Here, the drop ΔVD the voltage drop VD suitable value (e.g., 10V or less) if determined in, to reduce the difference between the mark voltage VO _M and the space voltage VO _S, the charge for the stray capacitance between the transmission line It is possible to suppress discharge and reduce the occurrence rate of communication errors.

  In the first invention, the transmission lines may be disconnected, for example, by detaching the communication cable, and when viewed from the power supply device, the state may be equivalent to that at the time of communication using the space signal. If such a state continues for a long time, when the voltage immediately before the stop of adjustment is held, for example, as a capacitor charging voltage, the load voltage VO decreases due to discharging. If the drop in the load voltage VO is large, even if the communication cable is connected and the normal state is restored, the load voltage VO necessary for flowing the mark current cannot be secured and normal communication cannot be performed. There is. In order to avoid such a problem, in the second invention (the invention according to claim 2), when the adjustment stop state of the output voltage from the constant voltage source continues for a predetermined time or longer, the adjustment of the output voltage is automatically performed. Try to resume.

  Further, the present invention can be realized not as a power supply device but also as a power supply method. A fourth invention (invention according to claim 4) is the power supply apparatus according to the method of the first invention realized as a power supply method, and the fifth invention (invention according to claim 5) is the invention of the second invention. The method of the power supply device is realized as a power supply method.

  According to the present invention, the output from the constant voltage source to the series connection circuit of the communication terminal device group between the transmission lines and the constant current source so that the drop voltage at the constant current unit becomes a predetermined constant value. Since the voltage is adjusted, an increase in the drop voltage in the constant current part is suppressed, and an increase in power consumption in the constant current part is prevented, and energy saving and space saving can be achieved. Also, during communication using a space signal, adjustment of the output voltage from the constant voltage source is stopped and the voltage immediately before the adjustment is stopped is maintained, so that the load voltage between the transmission lines drops at the constant current section. The drop of the drop voltage in the constant current part during communication using this space signal is set to an appropriate value, so that the mark voltage and the space voltage The difference can be reduced, charging / discharging of the stray capacitance between the transmission lines can be suppressed, the occurrence rate of communication errors can be reduced, and communication reliability can be improved. This makes it possible to achieve both energy saving and space saving and improved communication reliability.

  In addition, according to the present invention, when the adjustment stop state of the output voltage from the constant voltage source continues for a predetermined time or longer, the adjustment of the output voltage from the constant voltage source is resumed. When a state where the transmission line is disconnected continues for a long time, the adjustment of the output voltage from the constant voltage source is automatically resumed, and the load voltage necessary for flowing the mark current is increased. By being secured, communication can be performed immediately after recovery to a normal state.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a main part of an embodiment of a communication system according to the present invention. In this figure, the same reference numerals as those in FIG. 7 denote the same or equivalent components as those described with reference to FIG. In this communication system, the power supply device 1A has a configuration in which a voltage adjustment unit 1-3 and a voltage adjustment stop unit 1-4 are added to the conventional power supply device 1.

  The voltage adjustment unit 1-3 includes a chopper circuit 1-31 and a PWM control circuit 1-32, and the chopper circuit 1-31 includes a power transistor Q2, a diode D1, a choke coil L1, and a large switching element. The capacitor C1 has a capacity.

The power transistor Q2 switches the output voltage (constant voltage) VS from the constant voltage source 1-1 to convert it into a pulse voltage. PWM control circuit 1-32 inputs the voltage drop VD in the constant current unit 1-2, so that a constant value VD _MS which is determined this drop voltage VD advance, PWM to the gate terminal of the power transistor Q2 The duty ratio of the signal (control pulse voltage) V1 is adjusted. The power transistor Q2 is turned on when the PWM signal V1 is at "1" level, and is turned off when the PWM signal V1 is at "0" level.

Incidentally, a constant value VD _MS in the PWM control circuit 1-32 is defined as a set value of the drop voltage VD _M in the constant current portion 1-2 in the case where flow mark current IM to the constant current section 1-2 (30 mA) ing.

  In the chopper circuit 1-31, a connection circuit of the diode D1, the choke coil L1, and the capacitor C1 constitutes a rectifying / smoothing circuit 1-33. The rectifying / smoothing circuit 1-33 rectifies and smoothes the pulse voltage generated by the switching of the power transistor Q2, and adjusts the smoothed DC voltage VS ′ to the adjustment value (adjusted voltage) of the output voltage VS from the constant voltage source 1-1. And The adjustment voltage VS ′ is obtained as a charging voltage of the capacitor C1, and includes a communication terminal device group (master unit 2 and slave units 3-1 to 3-n) between the transmission lines L1 and L2, the constant current source 1-2, To the serial connection circuit (between terminals P1 and P2).

  The voltage adjustment stop unit 1-4 includes a comparator CP1, resistors R3, R4, R5, capacitors C2, C3, and a diode D2. The resistors R3 and R4 are connected in series via the diode D2 between the power supply voltage Vp (bias voltage generated from the constant voltage VS) and the ground line, and connected to a connection point P3 between the anode of the diode D2 and the resistor R3. The generated voltage V− is the first input voltage to the inverting input terminal of the comparator CP1, and the voltage V + generated at the connection point P4 between the cathode of the diode D2 and the resistor R4 is the second input voltage via the resistor R5. It is supposed to be given to the non-inverting input terminal.

  A capacitor C3 is connected between the non-inverting input terminal of the comparator CP1 and the ground line, one end of the capacitor C2 is connected to a connection point P3 between the anode of the diode D2 and the resistor R3, and the other end of the capacitor C2 is fixed. It is connected to a connection point P6 between the resistor R2 and the emitter of the transistor Q1 in the current unit 1-2.

  The output voltage Vcp of the comparator CP1 is given as a voltage adjustment stop / start signal to the PWM control circuit 1-32 in the voltage adjustment unit 1-3. The PWM control circuit 1-32 stops generating the PWM signal V1 when the output voltage Vcp of the comparator CP1 is at “1” level, and the PWM signal when the output voltage Vcp of the comparator CP1 is at “0” level. The generation operation of V1 is started.

[Reference example]
As a reference, FIG. 2 shows a circuit diagram of a communication system 200 in which the voltage adjustment stop unit 1-4 is removed from the power supply device 1A in the communication system 100 shown in FIG. Before describing the embodiment, characteristic operations and problems of the communication system 200 will be described first.

[When the number of slave units is reduced]
When the number of the slave units 3 is decreased, the load voltage VO between the transmission lines L1 and L2 decreases (point t1 shown in FIG. 3A), and the drop voltage VD in the constant current unit 1-2 increases ( (T1 point shown in FIG.3 (b)). Here, when the drop voltage VD for the constant-current unit 1-2 when the loop current I is marked current IM (30 mA) and VD _M, this drop voltage VD _M is the PWM control circuit of the voltage regulator 1-3 1-32. PWM control circuit 1-32 so as to drop the voltage VD _M from the constant current section 1-2 and the set value VD _MS, adjusts the duty ratio of the PWM signal V1 to the power transistor Q2. In this case, the duty ratio of the PWM signal V1 is reduced, and the ON time of the power transistor Q2 is shortened (see FIG. 3C).

As a result, the adjustment voltage VS ′ output from the voltage adjustment unit 1-3 decreases as shown in FIG. 3D, and the difference between the adjustment voltage VS ′ and the load voltage VO becomes small, and the constant current unit increase in the drop voltage VD _M in 1-2 is suppressed, so that the number of the sub-terminal 3 is maintained at the same value as before the decrease (t2 points shown in Figure 3 (b)).

In this way, in the communication system 200, if the reduced number of the sub-terminal 3, since increase of the drop voltage VD _M in the constant current portion 1-2 is suppressed, the power in the constant-current unit 1-2 Increase in consumption is prevented and energy saving is achieved. In addition, since heat generation due to power consumption in the constant current unit 1-2 is reduced, it is not necessary to take measures such as using a component with a large rating or adding a heat sink, and space saving of the power supply device 1B can be achieved. It becomes.

[When the number of slave units is increased]
As a reference, the operation when the number of handset 3 is increased will be described. When the number of slave units 3 is increased, the load voltage VO between the transmission lines L1 and L2 increases (point t1 shown in FIG. 4A), and the drop voltage VD at the constant current unit 1-2 decreases ( T1 point shown in FIG. 4B). Here, when the drop voltage VD for the constant-current unit 1-2 when the loop current I is marked current IM (30 mA) and VD _M, this drop voltage VD _M is the PWM control circuit of the voltage regulator 1-3 1-32.

PWM control circuit 1-32 so as to drop the voltage VD _M from the constant current section 1-2 and the set value VD _MS, adjusts the duty ratio of the PWM signal V1 to the power transistor Q2. In this case, the duty ratio of the PWM signal V1 is increased and the ON time of the power transistor Q2 is increased (see FIG. 4C).

As a result, the adjustment voltage VS ′ output from the voltage adjustment unit 1-3 rises as shown in FIG. 4D, and the difference between the adjustment voltage VS ′ and the load voltage VO increases, and the constant current unit reduction of drop voltage VD _M is suppressed at 1-2, will be kept to the same value as before the number of the sub-terminal 3 is increased (t2 points shown in Figure 4 (b)).

[Problems with the communication system 200]
In this communication system 200, when the handset 3 transmits a mark signal, the loop current I is set to the mark current IM (30 mA), and the mark current IM is stabilized by the operation in the constant current unit 1-2. When the communication signal is switched from the mark signal to the space signal, the loop current I is set to the space current IS (2 mA). The constant current unit 1-2 is designed to stabilize only the mark current IM. In order to maintain the loop current I at the mark current IM, the constant current unit 1-2 attempts to reduce the internal resistance. However, since the value of the space current IS is small, the loop current I cannot be returned to the mark current IM no matter how much the internal resistance in the constant current unit 1-2 is reduced, and eventually becomes the space current IS. . As a result, the drop voltage VD of the constant current portion 1-2 (VD _S) is reduced.

This drop voltage VD _S in the constant current portion 1-2 is provided to the PWM control circuit 1-32 of the voltage regulator 1-3. PWM control circuit 1-32, as a set value VD _MS drop voltage VD _S from the constant current unit 1-2 adjusts the duty ratio of the PWM signal V1 to the power transistor Q2. At this time, since the difference between the set value VD _MS and drop voltage VD _S large, the duty ratio of the PWM signal V1 from the PWM control circuit 1-32 increases. In this example, the duty ratio is 100%. As a result, the adjustment voltage VS ′ is significantly increased, and the load voltage VO is greatly increased. As a result, the difference between the mark voltage VO _M and the space voltage VO _S becomes excessive, the incidence of communication errors caused by charging and discharging of the stray capacitance CL between the transmission lines L1, L2 is high.

Embodiment
The communication system 100 shown in FIG. 1 solves the problem in the communication system 200. In this communication system 100, the power supply device 1A is provided with the voltage adjustment stop unit 1-4, and when the communication signal is switched from the mark signal to the space signal, the PWM control circuit 1-32 generates the PWM signal V1 (voltage adjustment). The adjustment operation of the output voltage VS in the unit 1-3) is stopped. In this way, as described below, the adjustment voltage VS ′ immediately before the adjustment stop is held in the capacitor C1, the rise of the load voltage VO is suppressed, and a communication error due to charging / discharging of the stray capacitance CL is prevented. The incidence is low.

FIG. 5 shows a time chart during communication in the communication system 100. (A) is a transmission waveform of the slave unit 3, (b) is a loop current I flowing through the transmission lines L1 and L2, and (c) is a reference voltage generated at a connection point P6 of the constant current unit 1-2. (Input voltage to the voltage adjustment stop unit 1-4) V _REF , FIG. 4D shows the input voltages V− and V + to the comparator CP1 in the voltage adjustment stop unit 1-4, and FIG. The output voltage (voltage adjustment stop / start signal to the PWM control circuit 1-32), FIG. 5F shows the PWM signal V1 from the PWM control circuit 1-32 to the power transistor Q2, and FIG. The adjustment voltage VS ′ output from the section 1-3, FIG. 11 (h) is the load voltage VO supplied between the power supply device 1A and the transmission lines L1 and L2.

[Switch from mark signal to space signal]
When the handset 3 switches the communication signal from the mark signal to the space signal (point t1 shown in FIG. 5A), the loop current I changes from the mark current IM (30 mA) to the space current IS (2 mA) (FIG. 5). (T1 point shown in (b)). Accordingly, when the reference voltage V _REF when the mark current IM flows is V _REFM and the reference voltage V _REF when the space current IS flows is V _REFS , the connection point P6 of the constant current unit 1-2 is The resulting reference voltage V _REF drops by V _REFM −V _REFS = ΔV _REF (for example, 2.5 V) (point t1 shown in FIG. 5C).

The change ΔV _REF of the reference voltage V _REF in the constant current unit 1-2 is given to the capacitor C2 of the voltage adjustment stop unit 1-4. At this time, since the voltage across the capacitor C2 cannot change instantaneously, the input voltage V− to the inverting input terminal of the comparator CP1 falls by ΔV _REF (point t1 shown in FIG. 5 (d)). As a result, the input voltage V− to the inverting input terminal of the comparator CP1 becomes lower than the input voltage V + to the non-inverting input terminal of the comparator CP1, and the output voltage Vcp of the comparator CP1 becomes the “1” level (FIG. 5 ( t1 point shown in e)). That is, the voltage adjustment stopping unit 1-3 detects the switching from the mark signal to the space signal, and sets the output voltage Vcp of the comparator CP1 to the “1” level.

When the output voltage Vcp of the comparator CP1 becomes “1” level, the PWM control circuit 1-32 in the voltage adjustment unit 1-3 stops generating the PWM signal V1 (point t1 shown in FIG. 5 (f)). That is, the output of the PWM signal V1 to the power transistor Q2 is stopped (locked). When the output of the PWM signal V1 is stopped, the power transistor Q2 is turned off, and the adjustment operation of the output voltage VS from the constant voltage source 1-1 in the chopper circuit 1-31 is stopped. At this time, the capacitor C1 of the rectifying / smoothing circuit 1-33 holds the adjustment voltage VS ′ immediately before the adjustment stop from the voltage adjustment unit 1-3 (point t1 shown in FIG. 5G). That is, the adjustment voltage VS _M ′ at the time of marking immediately before the stop of adjustment is held as the adjustment voltage VS _S ′ at the time of space.

Thus, the load voltage VO between the transmission lines L1, L2 will be raised by drop .DELTA.VD drop voltage VD of the constant current portion _{1-2 (ΔVD = VD M -VD S} ) ( FIG. 5 (h T1 point shown in FIG. Here, if determined to drop ΔVD drop voltage VD of the constant current portion 1-2 to the appropriate value, to reduce the difference between the mark voltage VO _M and the space voltage VO _S, the transmission lines L1, L2 between It is possible to suppress charging / discharging of the stray capacitance CL and to reduce the rate of occurrence of communication errors. In the present embodiment, as a result of calculation and measurement, the drop ΔVD of the drop voltage VD is determined to be 10 V or less as a value that can be charged and discharged with respect to the stray capacitance CL.

  After switching from the mark signal to the space signal, the input voltage V− to the inverting input terminal of the comparator CP1 gradually rises due to charging of the capacitor C2 via the resistor R3 by the power supply voltage Vp, and the comparator The input voltage V + to the non-inverting input terminal of CP1 gradually decreases due to the discharge from the capacitor C3 via the resistors R5 and R4. Further, the load voltage VO during the adjustment stop in the voltage adjustment unit 1-3 does not drop for a while because the adjustment voltage VS ′ immediately before the adjustment stop is held in the large-capacitance capacitor C1.

  In this case, the holding time of the adjustment voltage VS ′ by the capacitor C1 may be longer than the maximum space time. Further, the input voltage V− to the inverting input terminal of the comparator CP1 that gradually increases and the input voltage V + to the non-inverting input terminal that gradually decreases may not be reversed within the maximum space time. The maximum space time is defined by a communication protocol. For example, in asynchronous communication, one frame is 11 bits (START (1 Bit) + Data (8 Bit) + STOP (2 Bit)). Since the STOP bit is always “1”, the maximum space, that is, the number of consecutive “0” bits is nine. When the communication speed is 4800 bps, the maximum space time is about 2 msec.

[Switch from space signal to mark signal]
When the handset 3 switches the communication signal from the space signal to the mark signal (point t2 shown in FIG. 5A), the loop current I changes from the space current IS (2 mA) to the mark current IM (30 mA) (FIG. 5). (T2 point shown in (b)). As a result, the reference voltage V _REF generated at the connection point P6 of the constant current unit 1-2 is increased by ΔV _REF (point t1 shown in FIG. 5C).

The change ΔV _REF of the reference voltage V _REF in the constant current unit 1-2 is given to the capacitor C2 of the voltage adjustment stop unit 1-4. At this time, since the voltage across the capacitor C2 cannot change instantaneously, the input voltage V− to the inverting input terminal of the comparator CP1 rises by ΔV _REF (point t2 shown in FIG. 5 (d)). As a result, the input voltage V− to the inverting input terminal of the comparator CP1 becomes higher than the input voltage V + to the non-inverting input terminal of the comparator CP1, and the output voltage Vcp of the comparator CP1 becomes “0” level (FIG. 5 ( t2 point shown in e)).

When the output voltage Vcp of the comparator CP1 becomes “0” level, the PWM control circuit 1-32 in the voltage adjustment unit 1-3 starts the generation operation of the PWM signal V1 (point t2 shown in FIG. 5 (f)). That is, the output of the PWM signal V1 to the power transistor Q2 is resumed (unlocked). When the output of the PWM signal V1 is resumed, the power transistor Q2 is turned on / off, and the adjustment of the output voltage VS from the constant voltage source 1-1 in the chopper circuit 1-31 is resumed. Thus, the load voltage VO decreases, the flow returns to the mark voltage VO _M (t2 points shown in FIG 5 (h)).

  After switching from the space signal to the mark signal, the input voltage V− to the inverting input terminal of the comparator CP1 drops due to charging of the capacitor C3 through the path of the capacitor C2, the diode D2, and the resistor R5. Further, the input voltage V + to the non-inverting input terminal of the comparator CP1 increases due to charging of the capacitor C3 through the same path. Charging the capacitor C3 stops when the difference between the input voltages V− and V + to the comparator CP1 becomes equal to the voltage drop Vd at the diode D2.

[In case of abnormalities such as cable disconnection]
In this communication system 100, the transmission lines L1 and L2 may be cut off due to, for example, attachment / detachment of a communication cable, and when viewed from the power supply device 1A, a state equivalent to that at the time of communication using a space signal may occur.

  It cannot be predicted how long it will take for the cable to be removed. When such a state continues for a long time, the load voltage VO decreases due to the discharge from the capacitor C1 holding the adjustment voltage VS '. If the load voltage VO is greatly reduced, the communication cable is connected, and even if the normal state is restored, the load voltage VO necessary for flowing the mark current IM cannot be secured and normal communication cannot be performed. There is a fear.

  Therefore, in the communication system 100, when the adjustment stop state of the output voltage VS from the constant voltage source 1-1 in the voltage adjustment unit 1-3 continues for a predetermined time or longer, the adjustment of the output voltage VS is automatically resumed. I try to let them. Hereinafter, the operation (operation at the time of abnormality) will be described using the time chart shown in FIG.

For example, when the transmission lines L1 and L2 are cut off due to the attachment / detachment of the communication cable, no current flows through the constant current unit 1-2 (point t1 shown in FIG. 6A). However, the reference voltage V _REF generated at the connection point P6 of the constant current section 1-2 drops by a voltage ΔV _{REF that is} approximately the same as that at the time of the space current IS (point t1 shown in FIG. 6B).

The change ΔV _REF of the reference voltage V _REF in the constant current unit 1-2 is given to the capacitor C2 of the voltage adjustment stop unit 1-4. At this time, since the voltage across the capacitor C2 cannot change instantaneously, the input voltage V− to the inverting input terminal of the comparator CP1 drops by ΔV _REF (point t1 shown in FIG. 6C). As a result, the input voltage V− to the inverting input terminal of the comparator CP1 becomes lower than the input voltage V + to the non-inverting input terminal of the comparator CP1, and the output voltage Vcp of the comparator CP1 becomes the “1” level (FIG. 6 ( t1 point shown in d)).

  The PWM control circuit 1-32 in the voltage adjustment unit 1-3 stops the generation operation of the PWM signal V1 when the output voltage Vcp of the comparator CP1 reaches the “1” level (point t1 shown in FIG. 6E). When the output of the PWM signal V1 is stopped, the power transistor Q2 is turned off, the adjustment operation of the output voltage VS from the constant voltage source 1-1 in the chopper circuit 1-31 is stopped, and the rectifying / smoothing circuit 1-33. The capacitor C1 holds the adjustment voltage VS ′ immediately before the adjustment stop (point t1 shown in FIG. 6 (f)).

Thus, the load voltage VO between the transmission lines L1, L2 are shown in drop .DELTA.VD drop voltage VD of the constant current portion _{1-2 (ΔVD = VD M -VD S} ) only rises (shown in FIG. 6 (g) t1 point). Thereafter, the input voltage V− to the inverting input terminal of the comparator CP1 gradually rises due to charging of the capacitor C2 via the resistor R3 by the power supply voltage Vp, and the input voltage to the non-inverting input terminal of the comparator CP1. V + gradually decreases due to the discharge from the capacitor C3 via the resistors R5 and R4. In addition, the load voltage VO during the adjustment stop in the voltage adjustment unit 1-3 is gradually decreased due to the decrease in the adjustment voltage VS ′ due to the discharge from the capacitor C1.

  When the state in which the transmission lines L1 and L2 are disconnected for a long time continues, the input voltage V− to the inverting input terminal of the comparator CP1 becomes higher than the input voltage V + to the non-inverting input terminal (see FIG. 6C). T2 point shown). In this embodiment, the time until the input voltage V− becomes higher than V + is defined as the abnormality occurrence determination time tx, and this abnormality occurrence determination time tx is expressed as “maximum space time (for example, 2 msec) + margin time (for example, 8 msec). ) ”. As a result, the output voltage Vcp of the comparator CP1 becomes “0” level (point t2 shown in FIG. 6D), and the PWM control circuit 1-32 starts generating the PWM signal V1 (see FIG. 6E). T2 point shown).

PWM control circuit 1-32, as a set value VD _MS drop voltage VD _S from the constant current unit 1-2 adjusts the duty ratio of the PWM signal V1. At this time, since the difference between the set value VD _MS and drop voltage VD _S large, the duty ratio of the PWM signal V1 from the PWM control circuit 1-32 increases. In this example, the duty ratio is 100%. As a result, the adjustment voltage VS ′ is significantly increased (point t2 shown in FIG. 6F), and the load voltage VO is greatly increased (FIG. 6G).

  Note that charging of the capacitor C2 through the resistor R3 by the power supply voltage Vp and discharging through the resistors R5 and R4 from the capacitor C3 are caused by the difference between the input voltages V− and V + to the comparator CP1 at the diode D2. When the voltage drop becomes equal to Vd, the operation stops. The load voltage VO rises to the maximum value of the current source output (maximum load voltage: 65V, for example) while charging the stray capacitance CL between the transmission lines L1 and L2.

When the communication cable is connected and restored to a normal state, the loop voltage I returns to the mark current IM upon receiving the load voltage VO that has been increased to the maximum load voltage (point t3 shown in FIG. 6A). . As a result, the reference voltage V _REF generated at the connection point P6 of the constant current unit 1-2 is increased by ΔV _REF (point t3 shown in FIG. 6B).

The change ΔV _REF of the reference voltage V _REF in the constant current unit 1-2 is given to the capacitor C2 of the voltage adjustment stop unit 1-4. At this time, since the voltage across the capacitor C2 cannot change instantaneously, the input voltage V− to the inverting input terminal of the comparator CP1 rises by ΔV _REF (point t3 shown in FIG. 6C). The input voltage V− to the inverting input terminal of the comparator CP1 drops due to charging of the capacitor C3 through the path of the capacitor C2, the diode D2, and the resistor R5. Further, the input voltage V + to the non-inverting input terminal of the comparator CP1 increases due to charging of the capacitor C3 through the same path. Charging the capacitor C3 stops when the difference between the input voltages V− and V + to the comparator CP1 becomes equal to the voltage drop Vd at the diode D2.

When loop current I returns to mark the current IM, PWM control circuit 1-32, as a set value VD _MS drop voltage VD _M from a constant current unit 1-2, the PWM signal V1 to the power transistors Q2 Adjust the duty ratio. Thus, accompanied by discharge from the stray capacitance CL between the transmission lines L1, L2, the load voltage VO decreases, the flow returns to the mark voltage VO _M (FIG. 6 (g)).

Incidentally, downward movement to the upward movement and the mark voltage VO _M up load voltage with charge and discharge of the load voltage VO are the operation at the time of abnormality, it does not affect the normal communication.
In the above description, the case where the transmission lines L1 and L2 are cut off due to the connection and disconnection of the communication cable has been described as an example. However, the same applies when the actual space signal becomes longer than the abnormality occurrence determination time tx. It goes without saying that the operation is performed.
In the above description, the voltage adjustment in the voltage adjustment unit 1-3 is performed by the PWM control. However, it goes without saying that the voltage adjustment is not limited to the PWM control.

It is a circuit diagram which shows the principal part of one Embodiment of the communication system which concerns on this invention. It is a circuit diagram (reference example) of the communication system which removed the voltage adjustment stop part from the power supply device in this communication system. It is a time chart explaining operation | movement at the time of reducing the number of the subunit | mobile_units in this communication system (reference example). It is a time chart explaining operation | movement at the time of increasing the number of a subunit | mobile_unit in this communication system (reference example). 3 is a time chart for explaining an operation during communication (normal time) in the communication system (embodiment) shown in FIG. 1. It is a time chart explaining the operation | movement at the time of abnormality occurrence in this communication system (embodiment). It is a circuit diagram of the communication system which employ | adopted the conventional current loop system. It is a time chart explaining operation | movement at the time of normal communication in this communication system (when a communication cable is short). It is a time chart explaining operation | movement at the time of abnormal communication in this communication system (when a communication cable is long).

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Communication system, 1A ... Power supply device, 1-1 ... Constant voltage source, 1-2 ... Constant current source, 1-3 ... Voltage adjustment part, 1-31 ... Chopper circuit, 1-32 ... PWM control circuit, 1 -33 ... rectifying and smoothing circuit, 1-4 ... voltage adjustment stop unit, 2 ... master unit, 3 (3-1 to 3-n) ... slave unit, L1, L2 ... transmission line (transmission line), CL ... stray capacitance .

Claims (5)

In a power supply apparatus that supplies a voltage between transmission lines connected to a group of communication terminal apparatuses that perform communication by a current loop method using a first current value and a second current value smaller than the first current value.
A constant voltage source that outputs a constant voltage;
It is connected between the constant voltage source and the communication terminal device group between the transmission lines, and stabilizes the current flowing through the transmission line at the first current value during communication using the first current value. A constant current section;
Adjusting the output voltage from the constant voltage source to the series connection circuit of the communication terminal device group between the transmission lines and the constant current source, the drop voltage at the constant current unit is a predetermined constant value and And a voltage adjustment unit that holds the adjusted output voltage immediately before the adjustment stop when the adjustment is stopped,
A voltage adjustment stop unit that stops adjustment of an output voltage from the constant voltage source by the voltage adjustment unit during communication using the second current value. The power supply device according to claim 1,
The voltage adjustment stop unit restarts the adjustment of the output voltage when the adjustment stop state of the output voltage from the constant voltage source continues for a predetermined time or more. The power supply device according to claim 1,
The voltage adjustment stop unit is
A controller that adjusts the output voltage based on the drop voltage during adjustment,
And a voltage holding unit that holds the adjusted output voltage immediately before the adjustment is stopped when the adjustment is stopped. In a power supply method for supplying a voltage between transmission lines connected to a group of communication terminal devices that perform communication by a current loop method using a first current value and a second current value smaller than the first current value ,
A constant voltage source that outputs a constant voltage;
It is connected between the constant voltage source and the communication terminal device group between the previous transmission line, and stabilizes the current flowing through the transmission line at the first current value at the time of communication using the first current value. A constant current section,
During communication using the first current value, the output voltage from the constant voltage source to the series connection circuit of the communication terminal device group between the transmission lines and the constant current source is adjusted to adjust the constant voltage. The drop voltage at the current part is a predetermined constant value,
During communication using the second current value, adjustment of the output voltage from the constant voltage source is stopped so that the drop voltage at the constant current unit becomes the constant value, and adjustment immediately before the adjustment is stopped A power supply method characterized by holding the output voltage. In the power supply method according to claim 4,
The method of supplying power, wherein the adjustment of the output voltage is resumed when the adjustment stop state of the output voltage from the constant voltage source continues for a predetermined time or more.

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