DE3013342A1 - Multiple extension exchange line hold circuit - uses diode bridge and switchable thyristor with LED indication to hold exchange line loop - Google Patents

Abstract

A diode bridge, with thyristor, and LED indication circuits holds a telephone exchange connection whilst the telephone speech circuit is disconnected to talk to a further extension prior to transfer of the call to that extension. The diode bridge makes the controlling thyristor, which holds the exchange loop, independent of the voltage polarity on the exchange line. The diode bridge (D1-D4) is connected across the exchange line (L1, L2) at a point on the exchange side of the switch hook springset in the telephone and ensures the correct polarity on a Zener diode (Z2) and thyristor (T1) in the holding circuit. In normal condition the thyristor (T1) is non-conducting and no current is drawn from the exchange line. The thyristor (T1) is turned on by operating a key (Re to short the gate and anode. An LED may be connected in series with the thyristor to indicate a held line.

Description

Circuit arrangement for telephone sets

The invention relates to a circuit arrangement for telephone sets. It can be used in the state of keeping a connection, as in telephone systems occurs several times.

For telephone systems with two call stations on one subscriber line it happens, for example, that a connection is initially established by a call station and then to be taken over by the other sprechstelje.

In this case, the connection from the first call station must last as long be held until the second call station actually takes over the connection because if the handset is hung up too early at the first call station the existing connection is released and not from the second call station more can be taken over. The same state occurs when a participant has established a connection and would like to hold a direct query in the room. This is because the information about this query should often be sent over the telephone line connected remote participants are not known. In this case it is common to hold the microphone capsule closed with one hand during the consultation. This measure however, it is cumbersome and unreliable. In the previously described case the hold state during the transfer of an existing connection from a call station on the other hand, it is common to leave the handset of the first call station out of the Hand on until the second intercom has taken over the connection with certainty Has. In this case, however, it often happens that the handset is later forgotten of the first microphone unit on the cradle again. This leaves the first Call station later also after termination of the transferred connection for further ones Calls are barred until accidentally discovered by accident.

The technical task of the Sialtungsanordnung according to the invention consists in separating the speaking circuit of a call station without the subscriber line to separate.

There are already complicated ones in expensive telephone equipment electromechanical switching means that have a comparable holding state for a Enable connection.

However, these facilities are so expensive that they are not for ordinary telephone sets come into question.

The circuit arrangement according to the invention is characterized by a) a diode bridge connected between the voice wires of the subscriber line, b) a thyristor located in the cross arm of the diode bridge, which is in the conductive state represents a low resistance and in the locked state a high resistance, c) a non-latching pushbutton with a contact that shorts the thyristor unlocked by control electrode and anode, d) one in series with the thyristor in the shunt arm the diode bridge lying Zener diode, which together with the diode bridge and the Thyristor determines the voltage of the subscriber line at which the thyristor is blocked becomes e) and a bilateral zener diode that runs parallel to the diode bridge between the speech cores and protects the rest of the circuitry against overvoltages.

This circuit arrangement is cheap and reliable. The diode bridge makes the thyristor function regardless of the polarity of the voltage the subscriber line.

Another embodiment of the circuit arrangement according to the invention is characterized in that in place of the bilateral Zener diode between the speech veins one another normal zener diode occurs in parallel for series connection of thyristor and Zener diode in the cross arm of the diode bridge lies. In this way, too, the rest of the circuit arrangement can protect against overvoltage to be protected.

Developments and further developments of the invention can the Subclaims are taken.

The invention is described below in connection with an exemplary embodiment GESE explained the drawings, in which: FIG. 1 shows the basic circuit according to FIG Invention and Fig. 2 shows more detailed embodiments of the circuit arrangement according to the invention in connection with a normal subscriber set.

In Figure 1, the diodes D1 to D4 form a diode bridge between the voice wires L1 and L2 are switched. This point of the speech veins is available the hook switch. The diode bridge D1 to D4 ensures that the polarity the voltage of a Zener diode Z2 and a thyristor T1 is correct, whereby the Circuit arrangement becomes independent on the polarity of the voltage on the subscriber line.

In the normal state, the thyristor T1 is blocked, i.e.

it does not conduct, so the circuitry does not receive any current from the Takes up subscriber line and thus the transmission properties of the subscriber station unaffected. If the participant has a non-latching When the button is pressed, a contact R closes the anode with the control electrode of the Thyristor T1 short. If the voltage between the speech wires Ll and L2 is sufficient is high around the Zener diode Z2 - despite the low voltage drop across the diode bridge D1 to D4 and turn on the thyristor T1, then the thyristor is also turned on T1 conductive, the circuit arrangement draws current and the subscriber loop is over the circuit arrangement is closed.

So that the tension between the speech cores is higher than what is required Switch-on potential of the circuit arrangement described, it is necessary that the Disconnect the speech circuit of the subscriber set from the speech wires. These Switching action is carried out when the handset is back on the fork of the Hook switch is placed. The required operating sequence is therefore as follows the end: First the non-latching pushbutton must be pressed, then the handset must be hung up while the key is being pressed. The activation the circuit arrangement described is then a permanent state and the switching system does not appear as if the handset has been hung up around the subscriber line loop to open. Then the non-latching pushbutton can be released again The circuit arrangement remains in its operating state until the voltage on the subscriber line becomes lower than when it was switched on. This will only be the case when the The speech circuit of the participant set is reconnected to the speech wires will. This can be done either by having the handset at the same call station is picked up again, or by the fact that the handset is connected to another, parallel Is picked up. If the circuit arrangement described again except Operation was set, so the thyristor Tl returns to the locked state then the connection is released as soon as the handset is hung up.

The Zener diode Z2 determines the reverse voltage of the thyristor T1. the The only task of the bilateral Zener diode Z1 is in front of the diode bridge D1 to D4 in protecting the circuit arrangement from overvoltages that normally occur while the pulse dialing and when picking up and hanging up the handset. The bilateral Zener diode Z1 can also be replaced by a normal in the manner indicated by dashed lines Zener diode Z 'in the shunt arm of the diode bridge D1 to D4 are replaced, the parallel for series connection of thyristor T1 and Zener diode Z2. The bilateral zener diode Z1 is particularly useful as protection against inductively coupled high voltage.

The circuit according to FIG. 2 is very similar to the circuit according to FIG Figure 1, it contains some useful developments and refinements. Additionally In addition to the circuit parts according to FIG. 1, the circuit according to FIG. 2 contains three resistors R1 to R3 and a luminescent diode LED.

The resistors R1 and R2 protect against currents due to overvoltages. The resistor R1 protects the bilateral Zener diode Z1. The resistor R2 protects the diode bridge Dl to D4 and the switching elements in the cross arm of the diode bridge Dl to D4. The resistor R3 improves the operation of the thyristor T1 in this special application in which it does not react to sporadic changes in the Can address holding current, so as to secure the holding of the connection. The luminescent diode LED lights up when current flows through thyristor T1, this serves as an optical Signs that a connection is on hold.

On the other hand, hanging up the handset triggers a connection, if the luminescent diode LED does not light up.

Reference list of characters English German D1 Diode Diode D1 to D4 Diode bridge Diode bridge L1, L2 Line terminals Speech wires LED Luminous diode Luminescent diode Unstable pushbotten key contact R Contact Rl, R2, R3 Resistances Resistors T1 Thyristor Thyristor Z1 Bilateral zener diode Bilateral zener diode Z2, Z 'Zener diodes Zener diodes Empty side

Claims (6)

Claims)) Circuit arrangement for telephone sets for Separation of the speech circuit without disconnecting the subscriber line, marked by a) one connected between the speech wires (L1, L2) of the subscriber line Diode bridge (D1 to D4), b) one in the cross arm of the diode bridge (D1 to D4) Thyristor (T1), which has a low resistance in the conductive state and in the blocked state State represents a high resistance, c) a non-latching pushbutton with a Contact (R) that connects the thyristor (T1) by short-circuiting the control electrode and anode unlocked, d) one in series with the thyristor (T1) in the shunt arm the diode bridge (D1 to D4) lying Zener diode (Z2), which together with the diode bridge and the thyristor determines the voltage of the subscriber line at which the thyristor (T1) is blocked, e) and a bilateral Zener diode (Z1), which is parallel to the diode bridge (Di to D4) between the speech wires (L1, L2) and the rest of the circuitry protects against overvoltage. 2.) Circuit arrangement according to claim 1, d a d u r c h g e k e n n notices that in place of the bilateral Zener-Didde (Z1) between the Speech cores (L1, L2) another normal Zener diode (Z ') occurs: the parallel one for series connection of thyristor (T1) and Zener diode (Z2) in the cross arm of the diode bridge (Di to D4). 3.) Circuit arrangement according to claim 1 or claim 2, d a d u r c h g e k e n n n z e i c h n e t that in series with the thyristor (T1) and the Zener diode (Z2) a luminescent diode (LED), which is on when the subscriber line is on hold there is an optical sign. 4.) Circuit arrangement according to one of claims 1 to 3, d a d u It is noted that a resistor (R3) is parallel to the disturbance electrode-cathode path of the thyristor tT1) is the blocking of the Thyristor (T1) improved and made independent of potential fluctuations on the subscriber line. 5.) Circuit arrangement according to one of claims 1 to 4, d a d u It is noted that the diode bridge (D1 to D4) has a resistor (R2) is connected upstream of the diode bridge (D1 to D4), the thyristor (T1) and the Zener diode (Z2) and possibly the luminescent diode (LED) against overvoltage protects. 6.) Circuit arrangement according to one of claims 1 to 4, d a d u r c h e k e k e nn n e i c h n e t that the diode bridge (DI to D4) and the parallel-connected bilateral Zener diode (Z1) a resistor (Rl) is connected in series.