JPH0363866B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a DC loop type power receiving circuit that constitutes an interoffice relay line of an exchange, and particularly relates to a power receiving circuit that realizes constant voltage power receiving characteristics using semiconductors. .

An exchange not only performs exchange between subscribers connected to the exchange, but also performs exchange between subscribers of different exchanges by relaying information between exchanges. This relaying between exchanges requires a DC loop type power receiving circuit for the interoffice relay line as well as the power receiving circuit for the subscriber line.

A plurality of power receiving circuits for interoffice relay provided in an exchange are usually mounted at the same location due to equipment configuration considerations. Therefore, there is a strong demand for miniaturization of power receiving circuits, and reducing power consumption is an important factor for this purpose.

[Conventional technology]

Conventional power receiving circuits include methods using coils and methods consisting of electronic circuits, but both have constant resistance power receiving characteristics, and generate heat when power consumption reaches 0.5 to 1.5 W and a large number of circuits are grouped together.

FIG. 3 shows an example of a power receiving circuit using a conventional coil.

The DC current supplied from the DC power supply 11 of the opposing exchange via the dial pulse relay relay 10 and the relay line 15 is passed from the terminal 1 through the contact 4 of the power receiving circuit 8 to the equivalent inductance 6 of the coil 5 and the equivalent resistance. 7, and from terminal 2 to relay line 14
and returns to the DC power supply 11 via the relay 10.

The contact 3 of the power receiving circuit 8 is a contact for dial transmission, and is used when transferring the dial to the opposing exchange. During dialing, the contact 4 is opened and the coil 5 is separated from the relay circuits 14 and 15.

From the terminal 4WS through the 2-wire/4-wire conversion circuit 13 and the DC blocking capacitor 12, the relay line 1
4 and 15 are prevented from being attenuated by the coil 5, and are transferred to the opposite exchange via a DC blocking capacitor 9 of the opposite exchange.

The signal transferred from the opposite exchange passes through capacitor 9, trunk lines 14 and 15, and capacitor 12.
The signal enters the line/four-line conversion circuit 13 and is sent to the terminal 4WR.

Normally, the DC resistance of the relay 10 is about 400Ω,
The equivalent resistance 7 of the coil 5 of the power receiving circuit 8 is 100 to 500Ω
That's about it. Therefore, if the line resistance of the relay lines 14 and 15 is almost zero, the power consumption generated by the equivalent resistance 7 reaches a maximum of about 1.5W.

[Problem that the invention seeks to solve]

The above-described power receiving circuit having constant resistance power receiving characteristics generates a large amount of heat, and the temperature of a device in which a large number of power receiving circuits are mounted increases, making it difficult to miniaturize the device.

[Means for solving problems]

The above problem is solved by connecting the collector to the positive side of the DC power supply supplied from the relay line, connecting the emitter to the negative side of the DC power supply, and connecting the collector and the base with a resistor for current limiting, and connecting the emitter to the negative side of the DC power supply. A Zener diode that keeps the voltage between the collector and base constant is connected in series, and a transistor is connected between the base and emitter to reduce the AC impedance. This problem can be solved by providing it in the power receiving circuit.

[Effect]

In other words, a constant voltage is applied between the collector and base of the transistor connected to the relay line, and the alternating current impedance is lowered between the base and emitter. This is what was given to him.

This is based on the fact that the power supply device on the exchange side that supplies DC loop current usually has a resistance of about 400Ω, and even if the receiving side is short-circuited, it will be protected by this 400Ω resistance. We constructed a simple transistor circuit that has several constant voltage characteristics and exhibits high impedance characteristics for AC signals such as audio.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

DC voltage is applied from terminal 1 of the power receiving circuit to transistor 19 via resistor 16 and Zener diode 17.
A base current flows through the transistor 19. This base current is minute,
The voltage drop caused by the resistor 16 that limits the current flowing through the Zener diode 17 is almost negligible, and the voltage between the collector and base of the transistor 19 (hereinafter referred to as Vcb) is lower than that of the Zener diode 17.
is equal to the Zener voltage of

That is, Vcb becomes a constant voltage regardless of the collector currents of the transistors 19 and 20.
Therefore, the residual voltage between terminals 1 and 2 of the power receiving circuit is also constant, exhibiting constant voltage power receiving characteristics.

The current flowing through the transistors 19 and 20 returns to the DC power supply from the terminal 2 via the contact 3 for dial transmission, forming a loop current. capacitor 18
are Darlington connected transistors 19 and 2
Transistors 19 and 20 form a high impedance in terms of AC in order to lower the AC impedance between the base and emitter of transistor 19 and to prevent the base voltage of transistor 19 from changing due to signals such as audio along with resistor 16.

Here, for example, the residual voltage is set to 4, and the third
The voltage of the DC power supply 11 shown in the figure is 48, and the relay 10
When the resistance value of is 440Ω and the resistance value of the relay lines 14 and 15 is zero, the maximum loop current is 100mA, and the power consumption of the power receiving circuit is 0.4W.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

This uses a photocoupler 21 in place of the contact point 3 for dial transmission shown in FIG. When a dial pulse is applied between terminals 24 and 25, photocoupler 21 connects Zener diode 17.
Open and close the output of

When the photocoupler 21 cuts off the output of the Zener diode 17, the base voltage of the transistor 19 decreases due to the resistors 22 and 23, and the transistor 19 stops operating, so the transistor 20 also does not operate. The loop current between is disconnected.

When the photocoupler 21 connects the output of the Zener diode 17, the transistor 19 operates as in FIG. 1, forming a loop current between terminals 1 and 2 of the power receiving circuit.

〔Effect of the invention〕

As explained above, the present invention can significantly reduce the power consumption of the power receiving circuit compared to the conventional system, and has the effect of facilitating miniaturization of the device.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a diagram showing an example of a power receiving circuit using a conventional coil. In the figure, 3 and 4 are contacts, 5 is a coil, 6 is an equivalent inductance, 7 is an equivalent resistance, 8 is a power receiving circuit, 9, 12, and 18 are capacitors, 10 is a relay, 11 is a DC power supply, and 13 is a 2-wire /4-wire conversion circuit, 16, 22, 23 are resistors, 17 is a Zener diode, 19, 20 are transistors, and 21 is a photocoupler.

Claims (1)

[Scope of Claims] 1. A DC loop type power receiving circuit for a pair of inter-office relay lines of an exchange, in which a collector is connected to the positive side of a DC power supply supplied from the relay line, and a collector is connected to the negative side of the DC power supply. A resistor for current limiting and a Zener diode to keep the voltage between the collector and base constant are connected in series between the collector and the base, and an AC impedance is connected between the base and the emitter. A power receiving circuit for relaying between stations, characterized by having a transistor connected to a capacitor that lowers the power.