JPS6123453A - Interface circuit with trunk line - Google Patents

Abstract

PURPOSE:To miniaturize a transformer by closing a trunk line via a switch means and an emitter follower circuit to decrease a DC current flowing to the transformer when an incoming call is recognized at a trunk line connecting terminal. CONSTITUTION:A full wave rectifier circuit 7 comprising diodes D1-D4 is connected to a trunk line connecting terminal 5, and a series circuit 13 comprising a primary winding of a transformer 10 and an optional impedance circuit and an unsaturated emitter follower circuit 8 comprising a transistor (TR) and a resistor are connected respectively via a switch means 9 turned on when an incoming call is recognized at the trunk line connection terminal 5 of the output side. A current flowing to the primary winding of the transformer 10 is utilized to obtain a base current of a TRQ, which closes the trunk line.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an interface circuit for connecting telephones, answering machines, etc. to a central office line.

Conventional configuration and its problems In general, when connecting an answering machine to a central office line, the first
As shown in the figure, a transformer 3
An interface circuit configured to connect a telephone answering machine to the secondary side of the transformer 3 is used. However, in this type of device, when an incoming call is received at the central office line connection terminal 1 and the incoming call detection circuit 4 is activated to turn on the relay contact 2, a direct current flows through the relay contact 2 to the primary side of the transformer 3. If the current is very large, there is a problem in that a considerably large transformer 3 must be used.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide an excellent interface circuit that can significantly reduce the direct current flowing through the transformer with a simple configuration.

3 pages.

Structure of the Invention The present invention connects a rectifier circuit consisting of a diode to the office line connection terminal, and connects the transformer's primary winding to any arbitrary one via a switch means on the output side that is turned on when a call is received at the office line connection terminal. A series circuit consisting of an impedance circuit and a non-saturating emitter follower circuit consisting of a transistor and a resistor are connected respectively, and the pace current of the transistor is obtained using the current flowing through the primary winding of the transformer, which flows through the transformer. The structure is such that the current is significantly reduced by the transistor.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 is an electrical wiring diagram of an embodiment of the interface circuit of the present invention, in which reference numeral 5 denotes a station line connection terminal connected to the station line. Reference numeral 6 denotes an incoming call detection circuit which is connected to the office line connection terminal 1 via a capacitor C3 and detects when an incoming call is received at the office line connection terminal 1. 7 is a full-wave current circuit consisting of bridge diodes D1 to D4 connected to the station line connection terminal 1; Reference numeral 8 denotes a non-saturated emitter, which is composed of a transistor Q and a resistor R1, and is connected to the output end of the full-wave rectifier circuit 7 via a switching means 9 such as a relay contact, which is controlled on and off by the output of the incoming call detection circuit 6. follower circuit. 10, one end of the primary winding is connected to the output end of the full-wave rectifier circuit 7 via the switch means 9, and the secondary winding is connected to the output terminal 1.
1. A hybrid type transformer in which the centers of the -order windings are respectively connected to the input terminal 12, 13 is a resistor R2, R
This network is composed of three capacitors C2, one end of which is connected to the primary winding of the transformer 10, the other end of which is connected to the pace of the transistor Q via a diode D5.

The other end of the station line balancing network 13 is grounded via a capacitor C1, and forms a pre-circuit circuit between the primary winding of the transformer T and the station line in an alternating current manner.

In the embodiment described above, when there is an incoming call on the office line and an incoming signal is applied to the office line connection terminal 5, this is first detected by the incoming call detection circuit 6, and the switch means 9 is turned on. Therefore, in this state, the DC voltage applied to the office line 5 is applied to the full-wave rectifier circuit 7,
The voltage is applied to the collector of the transistor Q and the primary winding of the transformer 10 at a predetermined distance through the
The transistor Q is the primary winding of the transformer 10, and the resistor R3
, the current flowing through the diode D5 is made into a base current and conducts in a non-saturated state to close the station line. But □
In this case, the current flowing in the primary winding of the transformer 10 is 1/β(
β can be the current amplification degree of transistor Q),
Accordingly, a small transformer 10 and t with a small capacity can be used. In this embodiment, the signal from the office line is transmitted through the rectifier circuit 7, the switch means 9', and the transformer 10.
It flows through the primary winding, the station line balance network 3, and the capacitor C1, and is efficiently output to the output terminal 11 provided on the secondary side of the transformer 10. When Shingo is applied to the input terminal 12, it is transmitted from the primary winding of the transformer 10 to the office line through the switch means 9 and the rectifier circuit 7, and the truss 106
Almost no signal is transmitted to the secondary side of P and . That is, the input terminal 12 is connected to the center of the primary winding of the transformer 19, and the impedance seen from the center is equal between the station line balancing network and the station line. The same current flows through each winding in opposite directions with the center as a boundary, and almost no signal applied to the input terminal 12 flows into the secondary winding of the transformer 10. Therefore, according to the above embodiment, it is possible to easily connect a simultaneous call type answering machine without providing a special transmission/reception switching circuit. In other words, in the conventional interface circuit shown in Figure 1, the input and output terminals are common, so it is necessary to use a separate transmitting/receiving switching circuit by switching between the transmitting side during certain times and the receiving side during certain times. However, according to the above embodiment, since the input/output terminals 11 and 12 are separate and configured so that signals do not go around to each other, these terminals can be used to transmit and receive at the same time. Even with the recently developed 7-hour communication type answering machine, it is easy to connect the output terminal 11°1.
It has the advantage that it can be connected to 2.

Effects of the Invention As is clear from the above embodiments, the present invention connects a rectifier circuit consisting of a diode to the station line connecting terminal connected to the station line,
A non-saturated emitter follower circuit consisting of a series circuit consisting of the primary winding of a transformer and an arbitrary impedance circuit, a transistor, a resistor, etc., which is turned on when there is an incoming call at the station line connection terminal on the output side. The base current of the transistor is obtained by using the current flowing through the primary winding of the transformer, and the transistor is used to close the central line.The current flowing through the transformer is connected to the This has the advantage that the current can be considerably smaller than that required for connecting the station line, and that the capacity of the transformer can be made smaller and smaller accordingly.

In the embodiment, a hybrid type transformer having an intermediate tap in the primary winding is used as the transformer, and the input and output terminals are provided separately, but a transformer without an intermediate tap may be used as in the conventional case. . In addition, in the embodiment, a station line balancing network consisting of a resistor and a capacitor is connected in series with the primary winding of the transformer, but the station line balancing network described above may be composed of other electrical components such as a coil, a resistor, and a capacitor. It is also possible to configure the station line balancing network as an arbitrary impedance circuit.

[Brief explanation of the drawing]

Figure 1 is an electrical wiring diagram of a conventional interface circuit.
FIG. 2 is an electrical connection diagram of one embodiment of the interface circuit of the present invention. 5... Office line connection terminal, 6... Incoming call detection circuit, 7... Full wave rectifier circuit, 8... Non-saturated emitter follower circuit, 9... ...Switch means, 10...Transformer, 11...Output side terminal, 12...Input side terminal, 13...
・Station line balance network (impedance circuit)
, 1) +-1) 5... Diode, Q...
...Transistor, R1-I (,3...Resistor,
C1 to C3...Capacitors.

Claims (1)

[Claims] A current circuit consisting of a diode is connected to the office line connection terminal connected to the office line, and the output side of the current circuit is connected to the primary winding of the transformer and any impedance via a switch that turns on when there is an incoming call at the office line connection terminal. A series circuit consisting of a circuit, a non-saturated emitter follower circuit consisting of a transistor and a resistor, etc. are connected respectively, and the base current of the transistor is obtained using the current flowing through the primary winding of the transformer, An interface circuit with a central office line configured to connect the central office line via the switch means and the emitter follower circuit when a call is received at the connection terminal.