JPH0332149Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial field of application] This invention can be used in the event of a failure such as a power outage of a local telephone exchange.
This invention relates to a direct switching circuit for switching a central office line from a central office line circuit to an extension telephone.

[Conventional technology]

The central office line circuit of the private branch telephone exchange is equipped with direct switching, which switches the central telephone line from the central telephone circuit to the extension telephone, so that the central telephone line can be used even if the private branch exchange stops operating due to a failure such as a power outage. It has a circuit.

Conventionally, the above-mentioned direct switching circuit uses an electromagnetic relay (PF relay) having four switching contacts Pf ¹ to Pf ⁴ as shown in Fig. 2 to switch the extension telephone TEL-P from the extension circuit LC side to the central office line CO side. I was switching to

In other words, the station line circuit COC usually has 16
When the Hz ringing signal receiving circuit is prepared in the communication line TC and the extension telephone TEL-P is switched to the central office line CO side and connected directly to the central office line CO, bridging loss due to the impedance of the receiving circuit will occur. In order to prevent
Two switching contacts connect both lines of the working line to the communication line TC.
Pf ³ and Pf ⁴ were used to disconnect from the central line CO.

[Problem that the invention attempts to solve]

The use of electromagnetic relays having four switching contacts in electronic private telephone exchanges is a major hindrance to miniaturization and economicalization. In view of the above points, the present invention aims to reduce the number of contacts of electromagnetic relays and contribute to miniaturization and economicalization of electronic private telephone exchange equipment.

[Means for solving problems]

This invention uses diodes to make the polarity of the communication path non-polarized in the communication path of the central office line circuit of private telephone exchange equipment, which has recently been computerized, in order to create a DC loop using an electronic circuit or to receive a 16Hz ringing signal. This focuses on the fact that a bridge is inserted. In other words, during normal times (when the central office line is not in use), 16
It is waiting to receive a Hz ringing signal, and in this state, the relay contact for closing the DC loop is open, and the 16
Since the direct current is cut off by the capacitor for passing the Hz ringing signal, no direct current is flowing through the diode bridge, so the diode bridge is in a cut-off state. Furthermore, since the AC voltage generated by the audio signal is sufficiently smaller than the forward rising voltage of the diode, even if the AC voltage is applied to the diode, it will not become conductive and the diode bridge will maintain the cut-off state. Therefore, the AC signal due to the voice is blocked by the diode bridge and does not flow into the DC loop circuit. In other words, since the impedance for voice signals is sufficiently high and the bridging loss is extremely low, both lines of the communication path of the central office line circuit are
It is not necessary to disconnect from the central line using two switching contacts.

The present invention focuses on the above-mentioned points, and eliminates the two switching contacts by directly branching the switching circuit's switching circuit path from the office line communication path to the office line side and extension circuit side, thereby solving the above-mentioned problems. It is resolved.

[Configuration of Example]

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

The extension telephone TEL-P connects the office line CO directly to the terminals COT and COR of the direct switching circuit PET to the terminals TLT and TLR, and the extension circuit LC connects to the terminals STT and STR.
are connected to each other. (The symbol - is connected.) Terminals A and B of the office line circuit COC are connected to the extension circuit LC via the communication path switch SW. The extension circuit LC may accommodate a general extension telephone TEL or may accommodate a direct switching extension telephone TEL-P via the central office line direct switching circuit PFT.
There is a communication path section TC in the office line circuit COC, one end of which is connected to terminals A and B of the office line circuit COC, and the other end connected to the contacts Pf ¹ , Pf of the relay PF in the office line direct switching circuit PFT. ² break side and terminal COT, COR
It is connected to the. That is, the office line CO is directly branched and connected to the break side of the contacts Pf ¹ and Pf ² .

The communication line section TC in the office line circuit COC includes a 16Hz ringing signal detection circuit RC, a series circuit of a resistor R and a capacitor _C1 for passing the 16Hz ringing signal, and a DC loop for the central office line CO in parallel with this. Contact a of relay A (not shown) is connected for closing, and a diode bridge is connected for non-polarization.
DB, a DC loop circuit LP, a communication transformer T for coupling the communication path, and a capacitor _C2 for DC cutting are arranged in each communication path.

The configuration other than that described above is the same as that of a conventional private branch telephone exchange, so a description thereof will be omitted.

[Effect of the embodiment]

Under normal conditions, the relay PF in the station line direct switching circuit PFT
is driven by relay drive circuit RD and is always in operation. Therefore, contacts pf ¹ and pf ² of relay PF are switched to the operating side as shown by dotted lines.
Therefore, the extension telephone TEL-P is connected to the extension circuit LC through the following route and is used as a normal extension telephone.

Extension circuit LC-terminal STT/STR-contact pf ¹ /pf ²
(Operation) - Terminals TLT/TLR - Telephone TEL-P In the event of a failure such as a power outage, relay PF will automatically recover, and its switching contacts Pf ¹ and Pf ² will recover as shown by solid lines, so extension telephone TEL -P is the telephone TEL-P- terminal TLT/TLR- contact
pf ¹ /pf ² (recovery) - Terminal COT/COR - Switches to the central line CO side via the central line CO route.

In addition, the above route includes the communication line section within the central office line circuit COC.
By connecting the TCs in parallel, a loop is created to the central office line CO on the next route.

Office line CO-terminal COT-16Hz calling signal detection circuit
RC - Diode DB (~) - Diode DB (+) -
DC loop circuit LP - Diode DB (-) - Diode DB (~) - Resistor R - Capacitor C ₁ - Terminal COR
−Station line CO However, this loop has a diode bridge DB.
and capacitor C ₁ are connected in series, so as mentioned above, capacitor C ₁ prevents direct current from flowing from the office line CO, and diode bridge DB is in the cut-off state, so AC signals from audio cannot pass through. Therefore, bridging loss is extremely small and there is no problem with telephone calls.

To explain the above in more detail, in Fig. 1, when a direct line communication path is formed (when contacts pf ¹ and pf ² are restored, hereinafter referred to as direct communication), , the central line circuit COC is not activated and contact a remains open. Therefore,
During a call between the office line CO and the telephone TEL-P during direct communication, only an audio signal with no direct current superimposed, that is, an alternating current signal, is applied to the communication path section TC. The impedance of the communication transformer T is sufficiently large for this AC signal, and the impedance of the 16 Hz calling signal detection circuit RC and the series circuit of the resistor R and the capacitor _C1 is sufficiently small. Therefore, the circuit related to the voice signal of the communication path section TC can be represented by the equivalent circuit shown in FIG.

In Fig. 3, D ₁ to _{D 4} are the diodes constituting the diode bridge DB, Za is the AC impedance of the DC loop circuit, Z is the characteristic impedance of the communication path of the office line circuit COC as seen from the office line CO side,
Vmax indicates the maximum value of the audio signal voltage applied to the diode bridge DB, and _VF indicates the forward terminal voltage of each of the diodes _D1 to _D4 .

The positive and negative components of the audio signal are connected to diode _D1 and
Since it is applied to both ends of the series circuit of D ₂ and the DC loop circuit LP or to both ends of the series circuit of the diodes D ₃ and D ₄ and the DC loop circuit LP, Vmax<2・V _F +Vza …(1) However, Vza is If the relationship between the voltages across the impedance Za is established, a voltage higher than V _F will not be applied to each of the diodes D ₁ to D ₄ , so the diodes D ₁ to _{D 4} will not conduct depending on the audio signal, and will not conduct due to the audio signal. The diode bridge DB maintains the cutoff, and the audio signal is transferred to the diode bridge DB.
It will not pass.

By the way, when discussing the establishment of the relationship in equation (1) above,
Assuming that the voltage Vza across the impedance Za is 0 does not pose any problem in discussing the cut-off conditions of the diode bridge DB. That is, this assumption
This is because it directs the DB cut-off conditions in a safer direction. That is, the above condition will be discussed below as Vmax<2·V _F (2).

As is well known, in the case of a silicon diode, its forward terminal voltage V _F is within the range of 0.6 to 0.7V, so from the relationship in equation (2) above, the maximum value Vmax of the audio signal voltage is less than 1.2V. If so, the pupil diode bridge DB maintains the cut-off state and the audio signal does not flow to the communication path section TC.

By the way, as is well known, the maximum value Vmax of the audio signal voltage is determined by the following equation.

Vmax=√2・…(3) However, V is the effective value of the audio signal voltage It is also known that the following equation holds.

P=V ² /Z (4) where P is the audio signal level (power level), and the following equation is derived from equations (3) and (4).

Vmax=√2...(5) In equation (5), the characteristic impedance Z of the communication path
is the parallel impedance of the characteristic impedance Z _b of the telephone TEL-P and the impedance seen from the diode bridge DB of the communication path, so the relationship Zb > Z ...(6) holds, and equations (5) and (6) Then, the relationship Vmax<√2...(7) holds true.

By the way, as is well known, the audio signal level on the telephone line is set not to exceed OdBm, that is, the power level is set not to exceed 1mW, and the characteristic impedance Z _b of the telephone TEL-P is 600Ω. Since P=
Substituting 1mW (=0.001W) and Z _b =600Ω, we get Vmax<1.1(V) (8). In other words, during a direct call, a voltage of 1.1V or more is not applied to the diode bridge DB, so the relationship in equation (2) above holds, and during a direct call, the diode bridge DB does not apply to the voice signal. Therefore, there is no conduction, and the communication path section TC presents a sufficiently high impedance to the voice signal, so the bridging loss is extremely small.

In other words, the communication path section is connected in parallel to the communication path during direct communication.
Even if TC is connected, there is no problem with direct calls.

[Effect of idea]

As described above, the present invention reduces the number of switching contacts of a direct communication switching relay to a central office by half, and according to the present invention, remarkable effects regarding miniaturization and economicalization can be obtained.

In the embodiment, an electromagnetic relay is used as a direct switching means for automatic switching, but even when manual switching is performed using an electric key, the number of contacts can be reduced, as in the embodiment.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional example, and FIG. 3 is an equivalent circuit diagram of an audio signal circuit in an embodiment of the present invention. Main symbols: C ₁ ... Capacitor, COC ... Office line circuit, DB ... Diode bridge, LC ... Extension circuit, PF ... Direct switching relay, pf ¹ , pf ² , pf ³ ,
pf ⁴ ...Relay PF contact, PFT...Direct line switching circuit, RC...16Hz ringing signal detection circuit, RD...Relay drive circuit, TC...Communication line section of the office line circuit COC,
TEL...Extension telephone, TEL-P...Extension telephone.

Claims (1)

[Scope of utility model registration request] The extension telephone TEL is connected to the office line CO through the extension circuit LC, call path switch SW, and office line circuit COC in sequence, and the extension telephone
A part of TEL is an extension telephone TEL for switching directly to the central office line.
- In a local telephone exchange designated as P, the above-mentioned office line circuit COC has a diode bridge DB for non-polarization of the communication path in its communication path section TC, and a DC loop is closed to the office line CO. The extension telephone TEL-P for direct switching to the central office line has a normally open contact a of the relay for switching the relay, and a capacitor Cl connected in parallel with the normally open contact a for passing the calling signal. An extension telephone for switching directly to the central office line between the communication path and the communication path branched directly from the central office line CO.
Office line direct switching circuit PFT that switches and connects TEL-P
A central office line direct switching circuit characterized by being connected to.