JPS6120184B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a power supply circuit for a public telephone that charges a device to be charged by obtaining charging current from a central office line, and allows the device to supply power necessary for controlling calls and fee collection. Traditionally, public telephones have been used to store currency equivalent to call charges and to prevent unauthorized use.
It was equipped with various mechanisms and control circuits. Therefore,
A power source is required to drive these mechanisms and control circuits, and power sources include those that use the telephone exchange power supply as a power source via central lines, those that use commercial power, and those that have built-in batteries or storage batteries. The above three methods were used, using this as a power source. However, all of these conventional methods have some drawbacks. In other words, in the method of using the power supply of the telephone exchange described above, the power from the central office line is originally used for starting up the telephone exchange, restoring the telephone exchange, and making calls, and there is a loss due to the resistance of the central office line, so it cannot be supplied practically. There is a limit to electric power, especially instantaneous electric power, and it is not possible to directly supply enough electric power to drive the mechanism for smoothly storing coins and preventing unauthorized use. Therefore, only the relay that receives the coin storage signal is driven by direct power from the central office line, and all other mechanisms are mechanically configured to be driven by user input. Therefore, since there are many mechanical friction parts and timing is difficult to control, failures such as coin jams are likely to occur, increasing the possibility of unauthorized use due to artificial timing manipulation, and reducing the reliability of public telephones. The above-mentioned method of using a commercial power supply can supply enough current to drive not only the money handling mechanism but also the control circuit, so it is necessary to take measures to prevent money jamming and unauthorized use. This provides a highly reliable public telephone. However, public telephones using this method cannot be installed in areas without commercial power supply, and cannot be used during power outages, which limits the range of use. The method of using a built-in battery or storage battery as a power source as described above can be said to be a compromise of the methods described above, but the battery needs to be replaced every time it wears out, and in the case of a storage battery, it is necessary to replace the battery. There is a limit to the electric capacity of the battery, and the exhausted storage battery must be removed and charged, which complicates maintenance work and is not economical. In particular, since the internal volume of public telephones is limited, large-capacity storage batteries cannot be installed, so it is necessary to frequently charge the storage batteries using small-capacity storage batteries, which is extremely inconvenient in terms of maintenance. As a method that eliminates the disadvantages of the above three conventional methods, it is possible to collect a minute current from the office line through a high resistance when not on a call, charge a rechargeable storage battery, and discharge it during a call. . However, with this method, in order to prevent the telephone exchange from malfunctioning even if the line voltage fluctuates during non-call periods, the resistance value is set so that the charging current is within the allowable line current value at the highest voltage. When the voltage is the lowest, the charging current becomes extremely small, resulting in insufficient charging power, which makes it impossible to drive the control circuit sufficiently, resulting in reliability problems. Furthermore, if the storage battery is charged via a constant current circuit with a four-terminal network in order to eliminate the influence of voltage fluctuations between station lines, charging efficiency is also poor because not all of the station line current becomes charging current. As explained above, conventional public telephones have various drawbacks regarding the power supply, and improvements in this aspect have been desired. The present invention has been made to provide a public telephone set that solves these conventional drawbacks. In other words, a chargeable device such as a storage battery or a capacitor is used as a power source for a public telephone, and the charger is charged when the handset is connected and the handset is not connected, and when the handset is disconnected, that is, when a call is being made. A small charging current that does not interfere with the operation of the telephone exchange is supplied from the power supply of the telephone exchange through the central office line without any additional equipment on the telephone exchange side, and the electric power required for making calls, storing money, etc. The power that is continuously stored in this charged device at a small current is discharged at the required time with a current value of the required size,
The purpose is to ensure stable public telephone operation. Examples will be described below with reference to the drawings.
FIG. 1 is a circuit diagram showing one embodiment. In the figure, 1
1 is a telephone exchange, and its interior is equipped not only with a large-capacity DC power supply but also with a current supply circuit 3 for supplying current to the public telephone 2. This current supply circuit 3 is generally necessary for the telephone exchange 1 to be activated and restored by a telephone set. The telephone exchange 1 and the public telephone 2 are connected by central office lines _L1 and _L2 . The public telephone 2 is equipped with a calling circuit 4 necessary for making calls, and a control circuit 5 for charge calculation, coin storage, connection of the calling circuit, disconnection control, prevention of unauthorized use, etc. as circuits that require power. ing. Generally, when the handset is hung on the hook of a public telephone when not making a call, either or both of the central office lines _L1 and _L2 are connected to the telephone line 4 by the telephone switch HS.
The structure is such that it can be cut by. In FIG. 1, the central line _L1 side is disconnected by _HS1 , and the central line _L2 side is disconnected by a switch _HS2 . By using the conductive contacts of the hook switches HS ₁ and HS ₂ when not talking, when not talking, that is, when the handset is hung on the hook, backflow is prevented by forming a pritzge rectifier circuit with diodes D ₁ to _{D 4} . Station line L ₁ to rectifier circuit 6
are connected so that power can be collected from the office line with a constant polarity when no calls are made, regardless of the polarity of the office line. In the case of a telephone exchange where the polarity of the central office line does not change, the backflow prevention rectifier circuit 6 only needs to be provided with a diode _D6 in one direction as shown in Figure 2. In this way, the diode _D6 has a backflow prevention function. will be in charge of only Next, on the output side of the backflow prevention rectifier circuit 6,
A two-terminal network constant current circuit 7 consisting of a transistor TR ₁ , resistors R ₁ and R ₂ , and a Zener diode D ₅
connected to the charged device 8 via this constant current circuit 7.
It is configured to supply charging current to. The control circuit 5 is supplied with current from the device 8 to be charged. Here, a description will be given of the current that can flow from the telephone exchange 1 to the public telephone 2 when a call is not made. The current flowing from the current supply circuit 3 of the telephone exchange 1 to the public telephone 2 is monitored by a call loop monitoring relay (not shown), and when the current exceeds a certain office line allowable current value, the monitoring relay operates and the public telephone is closed. 2
It is now possible to detect when it is being used. Since this monitoring relay must be restored when a call is not made, a current higher than the restoration current value of the monitoring relay cannot be allowed to flow through the office line. This restoration current value is approximately 5mA in a normal telephone exchange.
That's about it. Therefore, when not talking, the central office line
For example, the current value that can be passed through L ₁ and L ₂ is slightly smaller than the allowable current value of the station line, taking into account manufacturing variations.
Must be set to a value of 3mA or less. For this reason, the current value flowing into the backflow prevention rectifier circuit 6 is always constant regardless of fluctuations in the station line voltage, for example.
A two-terminal network constant current circuit 7 is provided so that the current is 3 mA. That is, by providing a two-terminal network constant current circuit, malfunctions due to voltage fluctuations between station lines can be prevented. At the same time, since it is a two-terminal network, it can be connected in series with the device to be charged 8 so that the entire station line current becomes the charging current, making it possible to improve charging efficiency. 2
As the terminal network constant current circuit, a constant current diode _D15 using the constant current characteristics of the field effect transistor shown in FIG. 2 or a circuit shown in FIG. 1 can be considered.
The latter is superior to the former in that it allows fine current settings by adjusting resistor _R1 or _R2 . Next, the constant current circuit 7 shown in FIG. 1 will be explained. As shown in the figure, when using an NPN type transistor, connect a resistor R ₁ between the collector and base of the transistor TR ₁ , and connect a resistor R ₂ and a Zener diode D ₅ in series between the emitter and base. . With this configuration, one of the input voltages is applied to the collector, current flows in, and charging current is extracted from the connection point between resistor R ₂ and Zener diode D ₅ . Generally, the voltage applied between the central office lines L ₁ and L ₂ of a telephone exchange varies widely from 21V to 66V. The reason for this is that the settings cannot always be the same for public telephones installed anywhere due to the type of telephone exchange, the line resistance value depending on the thickness and length of the central office wire, and fluctuations in the power supply voltage of the central office, so the voltage may vary. occurs. An important role of the constant current circuit 7 is to absorb such voltage fluctuations and always supply a charging current within a range in which the response monitoring relay of the telephone exchange does not operate. FIG. 4 shows the relationship between input voltage and output current by comparing the two-terminal network constant current circuit and the four-terminal network constant current circuit shown in FIG. 3. As is clear from the figure, the amount of power consumed in the shaded area due to the bias current flowing through resistor _R3 in the four-terminal network constant current circuit is
It can be seen that the two-terminal network allows for better charging and is extremely effective. The operation of the circuit of the first embodiment configured as described above will be explained next. First, when the public telephone 2 is not in use and the handset is hung on the hook, if the _L1 side of the office line is positive and the _L2 side is negative, current will flow from the office line in the following path. , the device to be charged 8 is charged.

[Table] In this way, the constant current circuit 7 generates approximately
A current limited to 3 mA flows into the charged device 8 as a charging current. In this way, charging is performed during non-call periods. When you remove the handset from the hook and make a call, the circuit is disconnected from the hook switches HS ₁ and HS ₂ to the backflow prevention rectifier circuit 6, so no current flows, and the charged device 8 is discharged through the hook switch HS ₃ . , current is supplied to the control circuit 5. The embodiments of the present invention have been described in detail above, but the form of the circuit that collects the charging current from the station line is as follows:
It can be modified in various ways depending on the communication method. In particular, in the case of an AC signal system where the polarity of the office line is always constant, there is no need to use a backflow prevention rectification circuit or a bridge rectification circuit as the rectification circuit, and it is sufficient to simply insert a backflow prevention diode. In addition to the nickel-cadmium battery, the device to be charged may be a lead-acid battery, which is usually called a battery, or a large-capacity electricity storage device (commonly called a capacitor). Since the power supply circuit for the control circuit of a public telephone according to the present invention has the above-described configuration, it provides a public telephone that has a means for solving the aforementioned troubles such as money storage failure and unauthorized use without requiring a commercial power source. Moreover, it has the advantage of not requiring maintenance work such as charging the device to be charged. In addition, it is used in public telephones where the voltage between the office lines varies significantly, and even if the voltage between the office lines increases when there is no call, the current flowing from the office line is always constant, preventing malfunctions caused by exceeding the allowable line current. It never occurs. In addition, all incoming station line current can be converted into charging current, and even if there are fluctuations in station line voltage, charging can always be performed with the highest charging efficiency, and failures due to insufficient charging are less likely to occur. reliability,
The degree of utilization can be further increased.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing the first embodiment of the present invention, FIG. 3 is a four-terminal network constant current circuit diagram, and FIG.
The figure shows the characteristics of a constant current circuit. 1: Telephone exchange, 2: Public telephone, 3: Current supply circuit, 4: Call circuit, 5: Control circuit, 6: Backflow prevention circuit, 7: Constant current circuit, 8: Charged device.

Claims (1)

[Claims] 1. A chargeable device that can be charged and discharged as a power source for the control circuit of a public telephone, a backflow prevention rectifier circuit that is connected to the office line when not making a call, and a backflow prevention rectifier circuit that connects to the backflow prevention rectification circuit to In a power supply circuit for a control circuit of a public telephone, which is equipped with a constant current circuit that supplies a charging current to a public telephone, the device to be charged is connected to the control circuit during a call to enable current supply, and the device to be charged is connected to the control circuit when not in a call. A switching circuit is provided for disconnecting from the control circuit to block current supply from the charged device and for connecting the office line and the backflow prevention rectifier circuit; Therefore, all the station line current that is connected in series with only the device to be charged and flows into the backflow prevention rectification circuit with respect to the output of the backflow prevention rectification circuit during non-calling is considered to be a charging current, and the station line current that flows in for charging. A two-terminal network constant current whose output current value is set so that the value is a constant value slightly smaller than a predetermined station line current tolerance value during non-call periods of the telephone exchange connected to the public telephone set. A power supply circuit for a control circuit of a public telephone, characterized by comprising a circuit.