JPH0123038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching control circuit between an internal line and an external line in a call path of a key telephone device, and in particular, the switching control circuit can be optimally performed when the power supply to the main device is cut off, such as during a power outage. This invention relates to a switching control circuit.

In a small button telephone device, which has one line for communication with an outside line (hereinafter referred to as an outside line) and one line for communication between key telephones (hereinafter referred to as an extension line), the call line selection operation on the button telephone sets Many systems switch between an outside line and an extension housed in the main unit by restoring the operation of a relay in the main unit. In such a button telephone device with a call path switching system, when the power supply to the main device is cut off due to a power outage or the like while talking to the line connected by the operation of the call path switching relay,
When the above-mentioned switching relay is restored, the call circuit of the button telephone is immediately switched to the line that will be connected when the switching relay is restored, and especially if the restored side of the switching relay is an outside line, the outside line will be invalidated. This results in an undesirable disadvantage.

The present invention has been made to eliminate these drawbacks.

Embodiments of the present invention will be described below with reference to the drawings.

The drawing is a circuit diagram of an embodiment of the present invention, where M is the main device, CO is an outside line (for example, a central office line), and TEL is a circuit diagram of an embodiment of the present invention.
is a button telephone.

In the main device M, PRV is an extension telephone circuit, L
is the switching relay between outside line and internal line, l1 to l3 are the contacts of switching relay L, CNT is the line switching control unit, Q1
is a transistor for controlling the operation of switching relay L, Q2
is a transistor for slow and slow recovery control of switching relay L,
C is the slow recovery capacitor of switching relay L, PW
is the power supply section, R1 to R3 are resistors, D1 to D3 are diodes, CO1 and CO2 are external communication lines, P1 and P2
is an extension telephone line, T1 and T2 are key telephone TEL
C is a control line.

In the embodiment, the operating side of the switching relay L is for internal calls,
The recovery side is set to make an outside line call, and the configuration is such that even when there is no power input to the main device M, a call between the outside line CO and the key telephone TEL (external call) is possible.

When power is being supplied to each part from the power supply unit PW of the main device M and neither an outside call nor an internal call is occurring, when the power is turned on, the output OUT of the switching control unit CNT indicates the operation of the switching relay L. A signal (+ polarity signal) is sent, transistor Q1 becomes conductive (hereinafter referred to as on), and the switching relay L operates on the path of PW (+V) - D2 - L - Q1 (collector emitter) - ground. After the switching relay L operates, the ground is input to the input IN2 of the switching control unit CNT by its self contact l3, and the output is output.
The operation instruction signal sent to OUT is maintained, and the switching relay L continues to operate. That is, the switching relay L is configured to be a so-called always-operating relay, and the contacts l1 and l2 are switched to the dotted line side, and the communication lines T1 and T2 are connected to the extension communication circuit PRV.

First, a case of a call between an outside line CO and a key telephone TEL will be explained. External line selection information is input from the key telephone TEL that makes an external line call or responds to an incoming call from an external line via the control line C to the input INI of the switching control unit CNT in the main device M. A recovery instruction signal (earth potential signal) for the switching relay L is output from the output OUT of the switching relay L, and the transistor Q1 becomes non-conductive (hereinafter referred to as OFF). The switching relay L is restored, its contacts l1 and l2 are switched to the solid line side, and the next route "CO-CO1-l1 (restored) - T1-TEL-
T2-l2 (recovery)-CO2-CO", a communication path is created between the outside line CO and the key telephone TEL, and the key telephone TEL becomes capable of making outside calls.

In the above operation, the switching relay is restored immediately when the restoration instruction signal is sent to the output OUT of the switching control unit CNT (normal switching relay (depending on the recovery time), there is no delay in line switching operations.

Next, the case of an extension call will be explained. Although omitted in the figure, extension capture information, extension calling information from the key telephone TEL that originated the extension call,
Alternatively, various control circuits within the main device M perform known operations from calling the extension to establishing an extension talking state in response to response information from the called key telephone TEL.
When an extension call is established, an operation instruction signal (+ polarity signal) for the switching relay L is output from the output OUT of the switching control unit CNT, and the transistor Q1 is turned on. transistor Q
1 is turned on, the switching relay L is operating on the operating path of the switching relay L, and its contacts l1, l
2, l3 are switched to the dotted line side, and the call lines T1, T2 of the button telephone TEL are switched to the extension call lines P1,
It is connected to the extension call circuit PRV via P2, and ground is input to the input IN2 of the switching control unit CNT through contact l3 as operating information of the switching relay L, and is sent to the output OUT. The above-mentioned operation instruction signal is maintained, and the switching relay L maintains its operation. In this way, the key telephones TEL on both the calling side and the called side receive communication current from the extension call circuit PRV, and extension calls are made between the key telephones TEL.

Now, in the above extension call state, if the power supply from the power supply unit PW is cut off due to, for example, a power outage,
The +V voltage supplied to the output terminal of the power supply unit PW suddenly drops to the ground potential. Further, the output OUT of the switching control unit CNT also becomes the ground potential, and the transistor Q1 is turned off. Above power supply part PW
When the output terminal of the capacitor C becomes the ground potential, the voltage generated by the charge stored in the capacitor C causes the diode D2 to become reverse biased and turn off. As a result, the charge accumulated in the capacitor C becomes
The base current of transistor Q2 is first discharged in the path of "C-L-Q2 (emitter-base) - R3-earth", and the transistor Q2 is turned on.
-D3-l3(operation)-ground" maintains the operating state of the switching relay L. This operating state is maintained as long as the discharge current of the capacitor C is greater than or equal to the holding current of the switching relay L. That is, the switching relay L performs a slow and gradual recovery operation when the power supply is cut off. On the other hand, even during the slow recovery of the switching relay L due to the interruption of the power supply, the visible display (not shown) indicating that an extension call is in progress on the button telephone TEL goes out, making it impossible to make an extension call. This allows the button telephone TEL
If the person making an extension call notices an abnormality (i.e. power outage, etc.) and stops the extension call while switching relay L remains in operation, the call path via the key telephone TEL will be interrupted. Since the DC loop is cut off before capturing the outside line CO, there is no inconvenience such as erroneously capturing the outside line CO. In addition, if the power supply from the power supply unit PW is instantaneously cut off due to a power outage, etc., the information (earth potential signal) via the contact l3 of the switching relay L input to the input IN2 of the switching control unit CNT Since the extension call state is reproduced, the extension call state is maintained before and after the momentary power supply interruption.

As explained in detail above, in the present invention, the switching relay that switches the communication path does not perform a delayed restoration during restoration under normal control, but only performs a delayed restoration when the power supply is cut off, so power outages, etc. occur. The recovery delay time of the switching relay can be set to be sufficiently long when the call is interrupted, and the person making the call is given sufficient time to end the call. It is possible to prevent the line from being seized, and the effects of the present invention are extremely large.

[Brief explanation of drawings]

The drawing is a circuit diagram showing an embodiment of the present invention. M: Main device, TEL: Key telephone, CO: Outside line, PRV: Extension call circuit, CNT: Switching control unit,
PW: power supply section, L: switching relay, Q1, Q2: transistor, C: capacitor.

Claims (1)

[Scope of Claims] 1 Consisting of a main device and a plurality of key telephones connected to the main device, switching between an outside line and an extension is performed by a switching relay in the main device, and the switching relay is In a button telephone device that is an always-operating relay that recovers when the button telephone is making an outside line call, an operation instruction signal for the relay is sent from the button telephone when there is no call or when the button telephone is making an extension call, and when the button telephone is making an outside call, the button telephone device a switching control section that outputs a recovery instruction signal for each of the relays according to external line selection information; and a switching control section that is electrically conductive when it outputs the operation instruction signal and becomes non-conductive when it outputs the recovery instruction signal. a first transistor that operates or restores the switching relay, respectively; a capacitor that is charged when the power supply to the main device is continued; and a capacitor that charges the capacitor when the power supply to the main device is cut off. A diode that becomes non-conductive due to the voltage, and when the diode becomes non-conductive, a discharge current from the capacitor flows and becomes conductive, and the discharge current from the capacitor is supplied to the relay to restore the relay. A communication path switching control circuit having a second transistor for delaying.