JPH03123149A - Key telephone system - Google Patents

Abstract

PURPOSE:To prevent an unfaulty key telephone set from being misconceived to be faulty by stopping a feed from a main equipment for a prescribed time and bringing an internal circuit to self-release, when some abnormality is generated in the internal circuit. CONSTITUTION:When a disturbance surge voltage is applied and a CMOSIC for constituting a control circuit 5 is latched up, an output current from a power source circuit 4 increases and becomes an overcurrent, and an overcurrent detecting circuit 24 detects it and outputs an overcurrent detecting signal. A monostable multivibrator 22 is driven by using this overcurrent detecting signal as a trigger, outputs a timing pulse having prescribed time width (t), and a switch circuit 21 cuts off temporarily a feed to the power source circuit 4 of driving power supplied through a transformer 2 from a main equipment. As a result, the latch-up phenomenon is obviated, and after the time (t) elapses, the switch circuit 21 becomes an ON state, the feed is restarted and each circuit of the control circuit 5, etc., are brought to self-release. In such a way, it is prevented that an unfaulty key telephone set is misconceived to be faulty.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates generally to key telephone devices, and more particularly to electronic key telephone devices.

(Prior Art) Generally, an electronic button telephone device connects the main device and the button telephone, which is an extension terminal, with a cable of about 2 to 6 cores, and connects the main device to the button telephone by passing the cable through the main device. In addition to supplying driving power to the telephone, control data signals are exchanged between the main unit and the cables between other terminals and the button telephones, and control data signals are exchanged between the main unit and the cables between other terminals and the button telephones. Audio signals are exchanged between the two.

FIG. 3 is a block diagram showing the overall circuit configuration of the electronic key telephone device described above.

In FIG. 3, power is supplied from transformers 30a and 30b in main device 30 to transformers 2 and 3 in button telephone 20 through cable 1 with a DC voltage of 24V. The supply of driving power for the button telephone 20 from the main device 30 to the button telephone 20 through the cable 1 is called phantom power supply. The power supply circuit 4 in the button telephone 20 is a stabilized power supply circuit, and the power supply circuit 4 is connected to the transformer 2.
, receives power from the transformer 3 and outputs after stabilizing it to a DC voltage of 5V. The speech network 6 is driven by receiving a stabilized DC voltage of 5V supplied from the power supply circuit 4, and, under the control of the control circuit 5, connects the receiver and transmitter of the handset 8 with a predetermined audio signal. It controls the connection between the output sound source and the external telephone line. The transmitting amplifier 7a amplifies and outputs the audio signal from the microphone 11 under the control of the control circuit 5. The receiver amplifier 7b is driven by receiving a stabilized DC voltage of 5V supplied from the power supply circuit 4,
Under the control of the control circuit 5, the audio signal provided from the main device 30 through the cable 1 is amplified and output to the speaker 12. The control circuit 5 has a built-in one-chip CPU,
The above-mentioned speech network 6 is driven by receiving the stabilized DC voltage of 5V supplied from the power supply circuit 4.
, transmitting amplifier 7 a s controls the receiving amplifier 7 b and also controls the LED 9 for displaying the status of the telephone line.

Furthermore, a transformer 30a and a transformer 30b in the main device 30
The power supply circuit connected between the two is provided with a power supply 30c that outputs a 24V DC voltage, and is also provided with a protection circuit 31 such as a POSISTOR. When the power consumption of the button telephone 20 exceeds a preset value, the protection circuit 31 limits the amount of current supplied from the power supply circuit to the button telephone 20 through the cable node 1 by increasing the resistance value. I'm wearing a t-shirt as if to do it.

Note that the button telephone 20 is also provided with a button circuit for selecting a line.

FIG. 4 is a block diagram showing the internal configuration of the power supply circuit 4 included in the button telephone 20 shown in FIG. 3. As shown in FIG.

In FIG. 4, the switching transistor 41 operates in a 0N10FF state according to a timing pulse output from the error amplifier 42 to its base terminal, and supplies/supplies the drive power supplied from the main device 30 through the transformer 2 to the DC reactor 43 side. It is designed to be blocked. The DC reactor 43 and capacitor 50 constitute an LC filter. The error amplifier 42 has a built-in reference voltage circuit that generates a predetermined reference voltage, and also connects the reference voltage output from the reference voltage circuit to the signal line 45.
and the signal line 46 to the resistor 4.4 (:
) It also has a built-in comparator circuit, etc., which compares the pressure drop value f'ii and outputs a predetermined timing pulse according to the comparison result. The error amplifier 42 calculates the voltage drop value at the resistor 44 provided through the signal line 45 and the signal line 46 and the output from the reference voltage circuit so that the output voltage from the power supply circuit 4 is always a constant value (for example, DC 5V). A timing pulse is outputted, and the switching transistor 41 is controlled to be ON10FF so that the difference value between the reference voltage value and the reference voltage value set does not exceed a preset specified value.

That is, the error amplifier 42 performs feedback control on the voltage drop in the resistor 44 so that an abnormal voltage drop does not occur in the resistor 44 due to an overcurrent flowing through the resistor 44.

(Problems to be Solved by the Invention) In the button telephone device having the configuration shown in FIG. It is necessary to minimize transmission loss. Therefore, it is essential to form the internal circuits constituting the button telephone 20 using elements with as low power consumption as possible. The LED driver, decoder circuit, etc. that are currently used were formed using CMO8IC. In this way, since the internal circuit built in the control circuit 5 of the button telephone 20 is configured with a CMO8 IC which is a low power consumption element, the power supply circuit 4 of the button telephone 20 is connected from the power supply circuit in the main device 30. The DC voltage stabilized at 5V by the power supply circuit 4 is supplied to the control circuit 5.
If the internal circuits are operating normally, the power consumption in each internal circuit is on the order of 5VX (several mA to several tens of mA).

Incidentally, even if there is no abnormality in each of the internal circuits themselves, the internal circuits may not operate normally depending on the environment in which the key telephone 20 is installed.

That is, when the key telephone 20 is installed in an environment susceptible to disturbance surge voltage such as static electricity,
Disturbance surge voltages such as static electricity may be applied to the switch matrix 10 of the button telephone 20. When these disturbance surge voltages such as static electricity are applied to the switch matrix 10 of the button telephone 20 and mainly flow from this switch matrix 10 into the control circuit 5, the CMO8ICs constituting each internal circuit in the control circuit 5 will latch up. Due to this latch-up phenomenon, the CMO3 IC has a voltage of 5V different from normal operation.
A large amount of power, approximately x number 100+aA, is consumed.

However, if a current that is several times to several tens of times larger than the normal operation of each internal circuit in the control circuit 5 attempts to flow into each of the internal circuits, the power supply circuit of the main device 30 Since the inflow of abnormal current is limited to about several mA by the protection circuit 31, the button telephone 20 itself cannot operate and is in a stopped state. It is possible to prevent destruction in advance.

As mentioned above, the control circuit 5 has a built-in one-chip CPU as well as each of the internal circuits, but disturbance surge voltages such as static electricity may affect not only each internal circuit in the control circuit 5 but also the one-chip CPU. If this also affects the one-chip CPU, the one-chip CPU is likely to cause software runaway due to disturbance surge voltage such as static electricity. Therefore, W in the control circuit 5
, D, T, are provided with runaway prevention circuits.
One-chip CPL due to disturbance surge voltage such as static electricity.
The circuit is devised so that if a software runaway occurs in I, the one-chip CPU self-recovers by this runaway prevention circuit.

However, in the above configuration, the disturbance surge voltage such as the static electricity described above is mainly applied to the control circuit 5 from the switch matrix 10, and the CMO8IC of each internal circuit of the control circuit 5 latch-up due to the disturbance surge voltage such as the static electricity. Regarding the software runaway of the one-chip CPU when the one-chip CPU runs out of software, please refer to the above W.
One-chip C with runaway prevention circuits called D and T.
Even if the PU can self-restore, other internal circuits that have latch-up cannot be restored. Therefore,
When latch-up occurs in each internal circuit within the control circuit 5, there is a problem in that the key telephone 20 inevitably stops operating.

When such a problem occurs, users often assume that the key phone is damaged and return it to the service department for replacement with another key phone or as a return item for repair. Such items can account for nearly 50% of returned items. However, the latch-up phenomenon described above occurs when the power supply voltage is turned 0F.
This is a phenomenon in which the state is maintained as long as there is no FL, and it is accompanied by a thyristor effect that exhibits characteristics similar to those of a thyristor, so the power supply current will maintain latch-up when the key telephone 20 is disconnected from the main device 30. The latch-up phenomenon is canceled when the holding current becomes equal to or less than the required holding current.

Therefore, when the key telephone 20 is returned to the service department for repair due to a latch-up phenomenon occurring in each internal circuit in the control circuit 5, the key telephone 20 has already been disconnected from the main device 30 for return. As a result, the above-mentioned phenomenon does not reoccur and the phone continues to function normally, which not only causes great confusion in repair measures, but also significantly reduces the efficiency of repair work, and furthermore, creates a sense of distrust among users. sometimes occurred. Further, there is also an inconvenience for the user in that he or she is forced to perform extra work such as returning a key telephone that is actually not broken to the service department.

Therefore, the present invention has been made in view of the above, and its purpose is to prevent the main unit from operating when some kind of abnormality occurs in the internal circuit of the key telephone due to disturbance surge voltage such as static electricity being applied to the key telephone. By stopping the power supply from the power supply circuit to the button telephone for a predetermined period of time, and resuming the power supply from the power supply circuit to the button telephone after eliminating the abnormality that has occurred in the internal circuit due to the power supply stop, the button The internal circuits that make up the phone can self-recover, and a non-faulty button phone may be mistakenly recognized as faulty and brought to the service department, significantly reducing the efficiency of repair work, or the user may not be able to recover a non-faulty button phone. To provide a button telephone device that does not require extra work such as returning a telephone to a service department.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, a first aspect of the present invention provides a main device having a current limiting means for limiting a current supplied to the outside to a predetermined value or less, A button telephone that has a driving power supply means that receives electric power supplied from the main unit, variably adjusts it to a preset value, and then outputs it, and that transmits and receives voice and data to and from other terminals through the main device. In the button telephone device, the overload detection means detects and outputs when each part constituting the button telephone is overloaded, and the overload detection means detects when each part constituting the button telephone is overloaded. A power supply control means for cutting off the power supply from the main device to the driving power supply means for a preset time when it is detected that the drive power supply means has become a load is provided.

Further, in order to achieve the above object, a second invention of the present invention provides, in the button telephone device according to the first invention, the power supply control means is provided in the drive power source fj (provided within the supply means,
The drive power source 1jl is supplied from the main device.

When it is detected that each part constituting the button telephone is overloaded due to the magnitude of the power supplied to the power supply means, the power supply control means controls the output of the drive power supply means for a preset period of time. configured to block it.

(Function) According to the first aspect of the present invention described above, when the overload detection means detects that each part constituting the key telephone is overloaded, the key telephone is activated by the main device for a preset time. Since the power supply to the power supply means is cut off, even if each circuit in the button telephone configured with CMO8IC etc. causes a latch-up phenomenon, this latch-up phenomenon can be eliminated by cutting off the power, and the latch-up phenomenon can also be eliminated. After that, the power supply is restarted, so that each of the circuits self-recovers to normal operation. Therefore, the latch-up phenomenon occurring in each of the circuits described above can be resolved and self-recovery to normal operation can be performed without any extra work, and various problems that conventionally occurred can be eliminated. Ta.

Further, according to the second aspect of the present invention, the power feeding control means is provided in the drive power supply means, and each part constituting the key telephone is controlled by the amount of power supplied from the main device to the drive power supply means. The power supply control means cuts off the output of the drive power supply means for a preset time when it is detected that the drive power supply means has become a load, so that the increase in the number of circuit parts can be kept to the minimum necessary limit. In addition, it has become possible to achieve the above effects.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

The overall configuration of the button telephone device according to the present invention is substantially the same as that of the button telephone device having the configuration shown in FIG. 4, so a description thereof will be omitted.

FIG. 1 is a block diagram showing the main parts of a key telephone device according to an embodiment of the present invention. The outline of a button telephone device according to an embodiment of the present invention is as follows. That is, the first
In the figure, the button telephone 20 illustrated in FIG.
A switch circuit 21 is connected between the transformer 2 and the input side of the power supply circuit 4, a monostable multivibrator 22 is connected to this switch circuit 21, and a conzante 23 is connected to this monostable multivibrator 22. There is.

On the other hand, an overcurrent detection circuit 24 is connected to the output side of the power supply circuit 4, and the monostable multivibrator 22 is further connected to the output side of the power supply circuit 4.
is connected to a diode OR circuit 55 that ORs the output of the overcurrent detection circuit 24 and the output of the control circuit 5.

To explain the above-mentioned configuration in more detail, the switch circuit 2
1, the transistor Tr2 remains conductive unless a timing pulse signal of logic level "L" as described later is output from the monostable multi-bi break 22, and as a result, the transistor Tri also continues to maintain the conductive state. , receives power supplied from the main device 30 through the transformer 2 and outputs it as is to the power supply circuit 4.

The switch circuit 21 also includes a monostable multivibrator 2
When the transistor Tr2 becomes temporarily non-conductive due to output of a timing pulse signal as described later from the transistor Tr2, the transistor Trl also becomes temporarily non-conductive, and the power supplied from the main device 30 through the transformer 2 is reduced. The power supply circuit 4 is configured to temporarily cut off the supply to the power supply circuit 4.

The overcurrent detection circuit 24 is composed of, for example, a resistor, a transistor Tr3, etc. as shown in the figure, and the illustrated resistor has a resistance of several Ω (2
Ω to 10Ω), and by detecting the voltage drop across this series resistance, the button telephone 20
When the internal circuit is in an overcurrent state, an overcurrent detection signal is output. The diode OR circuit 55 receives the overcurrent detection signal output from the overcurrent detection circuit 24 and the runaway prevention circuit (W, D, T,) 5 built in the control circuit 5.
2 to 5 6 and the output reset signal 53.
Output to monostable multivibrator 22.

Here, the reset signal 53 output from the runaway prevention circuit (ν, D, T,) 52 is mainly caused by disturbance surge voltage such as static electricity that has entered the control circuit 5 through the switch matrix 10. This is output in order to reset the software runaway state when the one-chip CPU 51 enters a so-called software runaway state.

Note that the control circuit 5 includes the one-chip CP mentioned above.
In addition to U51 and runaway prevention circuit (enemy, D, T,) 52,
For example, an LED driver for driving the LED9,
A decoder circuit and the like are built in, and as mentioned above, the control circuit 5 consumes most of the power consumption of the button telephone 20 as a whole. Therefore, it is necessary to reduce this power consumption, and each of the above-mentioned parts built into the control circuit 5 is composed of a CMO3 IC, which is a low power consumption element. Moreover, most of the disturbance surge voltage such as static electricity that enters the button telephone 20 comes from the switch matrix 10, so each internal circuit in the control circuit 5
Latch-up phenomenon is likely to occur, and one-chip CPU5
1 is also prone to software runaway.

The monostable multi-bi break 22 has an overcurrent detection circuit 24.
The capacitor 23 connected to the monostable multivibrator 22 is driven by the output of an overcurrent detection signal from the diode OR circuit 55 through the diode OR circuit 55.
It is designed to output one timing pulse of logic level "L" with a time width t corresponding to the time width t determined by the capacitance of . The monostable multivibrator 22 is also triggered by the output of the reset signal 53 from the runaway prevention circuit (W, D, T) 52 through the diode OR circuit 55, and is driven for a period of time determined by the capacitance of the capacitor 23. One timing pulse of logic level "L" having a time width t corresponding to the width t is output.

In the above configuration, when a disturbance surge voltage such as static electricity enters the inside of the button telephone 20 from the switch matrix 10 of the button telephone 20, the disturbance surge voltage such as static electricity is mainly applied to the control circuit 5. When a disturbance surge voltage such as static electricity is applied to the control circuit 5, and the CMO5IC that constitutes the LED driver, decoder circuit, etc. in the control circuit 5 latches up, the output current from the power supply circuit 4 increases accordingly. This becomes a latch-up current.

Therefore, the output current from the power supply circuit 4 is several times higher than that when the CMO3ICs constituting each circuit are operating normally (for example, the output current during normal operation is 30 m
If it is A, it will be 300IIIA at latch-up.
500 mA).

In this way, when the output current from the power supply circuit 4 increases and becomes an overcurrent, the overcurrent detection circuit 24 detects this and outputs an overcurrent detection signal to the monostable multivibrator 22 through the diode OR circuit 55. do. The monostable multi-bi break 22 is driven by this overcurrent detection signal as a trigger, and outputs only one logic level "L" timing pulse with a time width t determined by the capacitance of the capacitor 23 to the switch circuit 21. . switch circuit 21
Based on this single timing pulse, the power supply of the drive power supplied from the main device 30 to the power supply circuit 4 is temporarily cut off (ie, for about a few seconds, the same time as the time t). As a result, the power supply from the power supply circuit 4 to the control circuit 5 and the like is naturally temporarily cut off.
When the current to the MO5I C drops below the above-mentioned holding current, the latch-up phenomenon is eliminated by the thyristor effect accompanying the latch-up phenomenon. Then, after the above-mentioned time has elapsed, the switch circuit 21 is turned on and power supply is restarted, whereby each circuit of the control circuit 5 recovers itself and operates normally again.

On the other hand, when the one-chip CPU 51 built in the control circuit 5 enters a software runaway state due to disturbance surge voltage such as static electricity, the runaway prevention circuit (W, D, T,) 52 detects the software runaway of the one-chip CPU 51. This software runaway should be prevented (9 0 Reset signal 53 is output. Runaway prevention circuit (W).

The reset signal 53 output from the D, T, ) 52 is
It is applied to the monostable multivibrator 22 through the diode OR circuit 55. Monostable multibibreak 2
2 is driven using this reset signal 53 as a trigger, and outputs only one logic level "L" timing pulse with a time width t determined by the capacitance of the capacitor 23 to the switch circuit 21, and the switch circuit 21 Based on this one timing pulse, the power supply of the drive power supplied from the main device 30 to the power supply circuit 4 is temporarily cut off in the same manner as described above. As a result, the software runaway of the one-chip CPU 51 is reset, and after the above-mentioned time has elapsed, the switch circuit 21 is turned on, power supply is restarted, and the one-chip CPU 51 returns to normal operation.

The above-described content mainly relates to the one-chip CPU 51, LED driver, and decoder circuit built in the control circuit 5, but it also applies to devices other than the control circuit 5 that constitute the button telephone 20, such as the speech network 6, Transmission amplifier 7a.

The present embodiment can also be effectively applied to a case where the receiver amplifier 7b and the like are constructed of CMO8 ICs.

As explained above, according to one embodiment of the present invention, disturbance surge voltage such as static electricity is mainly caused by the switch matrix 1.
0 into the control circuit 5 of the button telephone 20, causing a latch-up phenomenon in the LED driver, decoder circuit, etc. made of CMOSIC.
Even if the button telephone 20 becomes inoperable, the latch-up phenomenon will be immediately reset and it will self-recover to normal operation by turning on the power again, and the one-chip CPU 51
Even if software runaway occurs, this software runaway is immediately reset and self-recovery to normal operation when the power is turned on again. Therefore, as in the past, the button telephone 20
When a latch-up phenomenon occurs in each circuit that makes up the
- By disconnecting the button telephone 20 from the main device 30, there is no need to reset the circuits constituting the control circuit 5 from a stopped state to prevent thermal damage due to latch-up. In addition, the trouble caused by the user mistaking the above-mentioned problem as a malfunction and bringing the key telephone 20 to the service department, the inefficiency of repair work due to the inability to reproduce the problem, and the distrust of the service department toward the user. It is possible to resolve the issue.

FIG. 2 is a block diagram showing the main parts of a key telephone device according to another embodiment of the present invention. An outline of a button telephone device according to another embodiment of the present invention is that the functions of the switch circuit 21, multivibrator 22, capacitor 23, and overcurrent detection circuit 24 shown in FIG. 1 are realized in the power supply circuit 4'. This is what I did.

That is, in FIG. 2, the switching transistor 41
operates as 0N10FF by the timing pulse outputted from the error amplifier 42 to its base terminal, and the main device 3
0 through the transformer 2 is supplied to/cut off from the DC reactor 43 side. The DC reactor 43 and capacitor 50 are
It constitutes an LC filter. The error amplifier 42 has a built-in reference voltage circuit that generates a predetermined reference voltage, and also converts the reference voltage output from the reference voltage circuit and the voltage drop value at the resistor 44 provided through the signal line 45 and the signal line 46. It also has a built-in comparison circuit, etc., which compares the 2 and 3 and outputs a predetermined timing pulse according to the comparison result. The error amplifier 42 adjusts the voltage drop value at the resistor 44 provided through the signal line 45 and the signal line 46 and from the reference voltage circuit so that the output voltage from the power supply circuit 4' is always a constant value (for example, DC 5V). A timing pulse is output, and the switching transistor 41 is controlled to be 0N10FF so that the difference value between the reference voltage value and the output reference voltage value does not exceed a preset specified value. That is, the error amplifier 42 performs feedback control on the voltage drop in the resistor 44 so that an abnormal voltage drop does not occur in the resistor 44 due to an overcurrent flowing through the resistor 44.

Furthermore, the error amplifier 42 includes a multivibrator 4 which will be described later.
One timing pulse of logic level "H" with a predetermined time width t' is output from 7, and this one timing pulse and the voltage drop value at the resistor 44 applied through the signal line 45 and 46 are When a voltage signal with which The switching transistor 41 for a time width t'
is controlled to be in the OFF state.

The output side of the monostable multi-bi break 47 is connected to the error amplifier 42, and its trigger terminal is connected to the signal line 45, 46 through the error amplifier 42.
is connected to. A capacitor 48 is further connected to the monostable multi-bi break 47. The monostable multi-bi break 47 is configured to reduce the difference between the current flowing through the signal line 46 and the current flowing through the signal line 45 when an abnormal voltage drop occurs across the resistor 44, that is, when an overcurrent flows through the resistor 44. It is driven when the difference value exceeds a preset value and outputs only 11 timing pulses of logic level "H" having a time width t' determined by the capacitance of the capacitor 48 to the error amplifier 42. It has become.

In the above configuration, due to a latch-up phenomenon occurring in each circuit constituting the control circuit 5, the main device 30, the transformer 2, the switching transistor 4, etc.
When the current flowing into the resistor 44 through 1 increases abnormally, the difference value between the current input into the error amplifier 42 through the signal line 46 and the current input into the error amplifier 42 through the signal line 45 is Exceeds the configured value. In this way, when the difference value between the current flowing through the signal line 46 and the current flowing through the signal line 45 increases abnormally, the monostable multivibrator 47 is driven using this as a trigger, and as described above, the monostable multivibrator 47 is driven. A logic level "H2" with a time width t' determined by the capacitance.
Only one timing pulse is output to the error amplifier 42. The one timing pulse outputted from the monostable multivibrator 47 is superimposed on the voltage drop value across the resistor 44 which is applied to the error amplifier 42 through the signal lines 46 and 45, and therefore the voltage drop value is abnormally generated by the time width t'. A high voltage pulse is applied to the error amplifier 42. As a result, the error amplifier 42 determines that an abnormally large voltage drop has occurred across the resistor 44, and turns off the switching transistor 41 for a time corresponding to the time width t'.

After the time t' has elapsed, the control returns to the feedback control described above.

Therefore, since the switching transistor 41 is made non-conductive for the time t' determined by the capacitance of the capacitor 48 described above, the negative 1:1 side of the control circuit 5, etc. where the latch-up phenomenon occurs is temporarily connected to the power supply side. Thus, the latch-up phenomenon can be eliminated. Further, as the time t' elapses, the error amplifier 42 shifts to normal feedback control again, so that the power supply is restarted, and thereby each circuit built in the control circuit 5 etc. can self-restore. is now also possible.

As explained above, according to another embodiment of the present invention, the switching transistor 41 built in the power supply circuit 4' of the button telephone 20 can be used as the two switch circuits shown in FIG. In addition, since the resistor 44 can be used as the overcurrent detection circuit 24 shown in FIG. This can be achieved by keeping the amount to a minimum. Further, the error amplifier 42 provided in the power supply circuit 4' is generally implemented as an IC, but in other embodiments according to the present invention, it is a circuit that is relatively easy to implement as an IC, such as a monostable multivib break. Since the error amplifier 42 can be configured, the cost can be reduced. Furthermore, the one-chip CPU 51 undergoes soft runaway under the influence of disturbance surge voltage such as static electricity that has entered the control circuit 5, and the runaway prevention circuit (W, D, T,) 52, etc. causes the software runaway to be self-recovered. Even in such a case, the entire button telephone 20 can be easily reset to 7 8 with the above-described configuration, so one-chip C
It is possible to further improve the reliability of the self-recovery function of each part constituting the button telephone 20 including the PU 51.

〔Effect of the invention〕

As explained above, according to the first aspect of the present invention, when the overload detection means detects that each part constituting the 6-talk machine is overloaded, the -r set time is set. According to the second aspect of the present invention, a power supply control means is provided for cutting off the power supply from the main device to the drive power supply means and canceling the power supply cutoff after the elapse of the time period.
A power supply control means is provided in the drive power supply means, and when it is detected that each part constituting the button telephone is overloaded due to the magnitude of the power supplied from the main device to the drive power supply means, power supply control means is provided. Since the control means cuts off the output of the drive power supply means for a preset period of time, it is possible to prevent any abnormality from occurring in the internal circuit of the button telephone due to disturbance surge voltage such as static electricity being applied to the button telephone. When this occurs, the power supply from the power supply circuit of the main device to the button telephone is stopped for a predetermined period of time, and after the abnormality that has occurred in the internal circuit due to the power supply stop is resolved, the power supply from the power supply circuit to the key telephone is stopped. Resume Ru, Nitoyo, Mi, nl, jp 4 (Tan) The internal circuits that make up the telephone are able to self-recover, and a non-faulty button telephone is misidentified as malfunctioning and brought to the service department. It is possible to provide a key telephone device that does not significantly deteriorate the efficiency of repair work or require the user to perform extra work such as returning a non-faulty key telephone to a service department.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of a button telephone device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the main parts of a button telephone device according to another embodiment of the invention. 3
The figure is a block diagram showing the overall circuit configuration of a conventional electronic button telephone device, and FIG. 4 is a block diagram showing the configuration of a power supply circuit built into a conventional button telephone. 1... Cable, 4.4'... Power supply circuit, 5...
Control circuit, 20... Button telephone, 2]... Switch circuit, 22.47... Monostable multivibrator,
23゜48...Capacitor, 24...Overcurrent detection circuit, 30-...Main device, 30 c-D C24V power supply,
31... Protection circuit, 42... Error amplifier, 44...
・Resistor, 51... One-chip CPU, 52... Runaway prevention circuit.

Claims (1)

[Claims] 1. A main device having a current limiting means for limiting the current supplied to the outside to a predetermined value or less, and a main device that receives electric power supplied from the main device and variably adjusts it to a preset value. In the key telephone device, the button telephone device has a drive power supply means for outputting the power after the main device is activated, and transmits and receives voice and data to and from other terminals through the main device. an overload detection means for detecting and outputting a load; and an overload detection means for detecting that each part constituting the key telephone is overloaded, and for a preset period of time when the overload detection means detects that each part constituting the key telephone is overloaded. A button telephone device comprising: power supply control means for cutting off power supply from the device to the drive power supply means. 2. In the button telephone device according to claim 1, the power supply control means is provided in the drive power supply means, and the key telephone device is controlled by the magnitude of the power supplied from the main device to the drive power supply means. A button telephone device, characterized in that, when detecting that each constituent part is overloaded, the power supply control means cuts off the output of the drive power supply means for a preset time.