JPS62217791A - Polarity inversion detection circuit - Google Patents

Abstract

PURPOSE:To reduce a current at an LED side and to obtain small-sized trunk line interface by taking polarity inversion detection information out of the photocoupler bus of a serial circuit at the time of inverting the polarity of a trunk line. CONSTITUTION:Normally the contact point of a switching relay S is turned on so as to form an outgoing loop. At the time of inverting polarity, a contact point S1 is turned on the same as a normal state. The light emitting diode PC1 of the photocoupler emits light, and the polarity inversion information is transmitted to the OUT terminal of the photocoupler. The PC1 never enters a DC loop at a normal state and at the time of inverting polarity, whereby an electronic synchronization circuit at a latter stage, which satisfies the limit condition of a DC resistance viewed from L1 and L2, can be easily constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a polarity reversal detection circuit used in a central office line trunk interface of a switching device.

(Prior art and its problems) In recent years, the subscriber line interface of PBX and key telephone equipment has been computerized, and LS, generally called 5LIC, has been computerized.
I and HIC are appearing. As computerization progresses in this way, the parts of the system components that have been computerized and the parts that have not been computerized will be extremely unevenly mounted, and the mounting unit dimensions will inevitably become uneven. Compared to PBX and key telephone equipment, the extension side interface is becoming increasingly electronic.
The station line side interface still uses large transformers, relays, and large capacitors.

This is because the applied DC voltage 1 incoming signal is excessive, and the current capacity also requires a hundred and several tens of mA, and is also for lightning protection.

In the current telephone switching network, when communicating between telephone terminals,
It is necessary to detect the reversal of power supply polarity between stations 'ffAL, t, and z. For example, in private branch exchange equipment, it is necessary to detect the polarity reversal sent by the station when the other party answers the call. Furthermore, when a call is received, a polarity reversal sent from the station is detected almost simultaneously with the ringing signal, and an automatic response or collision prevention function may be realized. In such a switching device, it is necessary to detect a change in polarity.

Next, a conventional circuit is shown in FIG. Here, L l+L2
is the subscriber line (office line) terminal, RA is the incoming call detection circuit, T is the voice coupling transformer, PC is the photocoupler for detecting polarity reversal, D is the reverse voltage protection diode of the PC, and RL is the dial pulse sending circuit. Our dial pulse sending relay, re is its contact, C is the spark absorption capacitor, R is the spark absorption resistor, S is the switching relay, SL is its contact, SW
is a communication path switch, and . . . . n are terminal telephones.

To explain the operation when making a call to the central office line via the call path switch SW based on the call operation of the terminal telephone device (for example, station), first, a collision prevention detection circuit (not shown) connects the L2 terminal and the earth (ground). ) to determine whether a ringing signal (polarity inversion) is being applied.

If there is no signal, a loop forming signal is output to turn on the S relay, and the S contact closes (state shown).

At the same time, the RL relay is turned on and the rl contact is closed to form a DC loop, but if there is a signal, it is assumed that the station line is busy, and the same process is performed for the next station line, and for the operation of the station line transmission. This prevents collision with the call signal. After forming the loop, dial pulses will be sent, but first, RL
After the relay is turned on and the rl contact is closed,
The rll contact is opened by the dial selection signal and a dial pulse (10/20 PPS) is sent to the office line.

In the circuit of FIG. 1, when L is positive and L2 is negative, 1. The light emitting diode side of the photocoupler PC does not emit light, and the polarity inversion information at the polarity inversion information output terminal OUT outputs the old GH (+5V). When L+ is negative and L2 is positive, the light emitting diode of the photocoupler emits light and outputs LOW (OV) as polarity reversal information, so it is possible to detect that the polarity has changed. This photocoupler PC is required to flow approximately 120 mA.

Inevitably, general-purpose photocouplers do not have enough current capacity, making photocouplers expensive and large in size. Also,
Approximately 120 mA must be passed through the transformer T, which is also expensive (it requires a large size, and the inductance cannot be large, making it difficult to obtain crosstalk characteristics below a certain value due to the coupling characteristics due to leakage magnetic flux between the transformers). It is.

Recently, computerization has been progressing in order to eliminate this large transformer. An example of this electronic circuit is shown in FIG. Here, T1 is an audio coupling transformer, C1 is a capacitor that cuts the direct current flowing through the transformer, PC is a photocoupler for detecting polarity reversal, Dl is a diode for reverse voltage protection of the photocoupler PC, ■ is a diode bridge, and 2 is a diode bridge. The electronic sink circuit is a circuit that exhibits a resistance value of about 50 to 300 ohms in direct current and a resistance value close to infinity in alternating current. 3 is a dial pulse sending circuit.

To explain the operation when transmitting a station line, first, the collision prevention IJ:, detection circuit (not shown) connects the [5, terminal and ground (
1.71 to determine whether a calling signal (polarity inversion) is being applied.

Here, if there is no signal, a loop forming signal is output and S
Turn on the relay, S, contact closes (state shown),
At the same time, the dial pulse sending circuit operates to form a DC loop, but if there is a signal, it is assumed that the office line is busy, and the same goes for the next office line, and it is used as a ringing signal for the operation of calling the office line. This prevents collisions.

On the other hand, the electronic synchro path 2 is required to pass a direct current but not an alternating current. For this reason, this sink circuit is driven by an input obtained by smoothing the voltage between A and B in the figure. The dots in the figure are the above-mentioned smoothing voltages.

The operation when sending out dial pulses is as follows. When making a dial, use the TT that supports dial operation.
L level or C-MOS level dial signal input is L
becomes OW, (L, →I), -diode bridge 1-
Current loop of electrification sink circuit 2 - dial pulse sending circuit 3 → diode bridge 1 → S, → L2) or (L2 → SI → diode bridge 1 - electrification sink circuit 2 - dial pulse sending circuit 3 - diode bridge 1) =PC-Ll) is formed. Therefore, the capacitor C2 is charged, and then the transistor Q is turned on, and the electronic sink circuit 2 is operated. At dial break, the dial signal is HIGH, and the charge stored in the capacitor C2 is mainly discharged through the base of the transistor Q and the resistor R3. moreover,
A portion of the current is discharged through resistor R2, but this current is small compared to the former.

Incidentally, when making the dial, the electronic sink circuit 2 must be driven immediately after the meter, and a DC loop must be formed for Lz. However, since the charge on capacitor C2 has decreased, charging is performed first. after that,
Transistor Q is turned on and electronic synchro path 2 performs normal operation. As explained above, when viewed from L and L2,
When transmitting dial pulses, there is also the drawback that the transmitted dial pulse waveform is deformed because time is required to charge the capacitor C2 when transitioning from break to make.

The transformer TI in the figure cuts off the direct current with the capacitor C1, and does not allow the aforementioned current of about 120 mA to flow to the transformer T.
It is sent to electronic synchro path 2. Therefore, it is not necessary to use the large transformer shown in FIG. 1, and the transformer T1 is miniaturized. However, it is still necessary to supply about 120 mA to the photocoupler PC for polarity reversal detection, and the size is large and the price is high. Furthermore, when the dial pulse sending circuit is in the on state, the DC resistance seen from L1 and L2 must be 50 to 300Ω. The voltage drop in the forward voltage on the light emitting diode side of the photocoupler PC or the forward voltage of the diode D makes it difficult to satisfy the above-mentioned direct current resistance restriction. As described above, conventional polarity reversal detection circuits cannot be made smaller or lower in price.

(Purpose of the Invention) The present invention provides a polarity reversal detection circuit that has a circuit configuration that allows the use of general-purpose small photocouplers without using these large photocouplers, thereby reducing the size and cost. The purpose is to

(Structure of the Invention) To achieve this object, the polarity reversal detection circuit of the present invention has a series circuit in which a photocoupler path and a resistor are connected in series. In polarity,
When a DC loop is formed, it is connected between the office lines, and when a dial pulse is sent out, the DC impedance of the series circuit becomes extremely large, and when the polarity is reversed, it is activated to extract polarity reversal detection information from the photocoupler path. It is configured. Here, the photocoupler path may include a series path in which a light emitting side of a photocoupler and a diode are connected in series with the same polarity, and a light receiving side of a photocoupler coupled to the light emitting side of the photocoupler. .

(Example) The present invention will be explained in detail below.

FIG. 3 is a diagram showing an embodiment of the present invention. Here, the same reference numerals as in FIGS. 1 and 2 indicate the same items. PCl
is the photocoupler, D is the protection diode of the photocoupler PC, D2 is the normal battery D t ,
A diode that deactivates the Ra path, Q I-Q a
is a transistor, RIR5+Rh, R? ,Rll+R
q is resistance. The operations of the switching relay SI and the dial pulse sending circuit 3 described above are the same as those in the prior art, so the explanation thereof will be omitted.

Further, 21 is an electronic synchro path having a resistance value of about 50 to 300 Ω in direct current and a value close to infinity in alternating current, and 31 is an electronic dial pulse sending circuit. now,
A case in which central office lines L + and L z are captured via the call path switch SW based on a calling operation of a terminal telephone device (for example, a station) and then a dial operation is performed will be sequentially explained. Note that R+ and Rz both have a resistance value of about 10Ω, and the resistor R3 has a resistance value of, for example, about 20Ω. The electronic sink circuit 21 is used as a DC loop forming circuit, and is required to pass a direct current but not an alternating current. For this reason, the voltage between AB in the figure is divided by resistors R+ and R2, and the charging current flowing through forward diode D3 is accumulated in capacitor C2 and the smoothed input is used to drive transistor QI in the synchro path. ing. The dots in the figure are the above-mentioned smoothing voltages. PC2 is a photocoupler that constitutes an optical coupling switch. When the dial signal (HIGH) is input, the transistor Q2 is turned on and the photocoupler PC2 is activated.

When the dial is made, the light indicates a predetermined smoothed voltage, but when the dial breaks, the current i3 in the diagram is connected to the photocoupler P.
It attempts to discharge through the light emitting diode side of ct and resistor R2. When discharge occurs, the charge on capacitor C2 disappears. When the next dial make occurs in this state, the capacitor C2 is first charged, so the electronic sink circuit 21 cannot be immediately driven to form a DC loop.

Therefore, at the time of dial break, the transistor side of the photocoupler PC2 is turned off to prevent the current i3 from flowing. Furthermore, for stabilization, a diode D3 is inserted to prevent the current 12 from flowing. As a result of the above, the capacitor c2 remains charged during the dial break. When the next dial make occurs, the electronic sink circuit 21 is immediately driven to form a DC loop.

Next, the electronic dial pulse sending circuit 3I will be explained. When a dial operation (HIGH) is input during dial sending, it is inverted by an inverter (INV) and its inverted output becomes LOW.

First, the TT supports dial operation when making dials.
When the L level or C-MOS level dial signal input is inverted by the inverter INV and becomes LOW, (Qi O
F F-P Cx OF F-QaON-QS ON]
The operation becomes (L2-s, - diode push 1 (+
)-electronic sink circuit 21-Qs-diode bridge 1(-)→Ll) loop is formed and output as a make signal. Next, at the time of a dial break, when the dial signal input mentioned above is inverted at the impark INV and becomes HIGH, (QION→PC30N-Q, OFF→QSOFF
], and (i, z-3, - diode push 1
(+)-Electronic sink circuit 21 = Qs (OF
)-diode bridge 1(-)-Ll) loop is opened and output as a break signal. Note that the path (P C:l collector/emitter→Rs) enters in parallel into the “open” loop. Here, resistor R5 is 1
By setting 00 to a value sufficiently higher than Ω (for example, 200 to Ω), it is possible to satisfy the condition of 100 to Ω or more, which is necessary to detect a break on the station side. Note that the resistance R
4 is too large to drive the transistor QS, the transistor Q may be replaced by a Darlington circuit.

In this way, the dial signal can be sent out by simultaneously controlling the photocouplers PC2, PC and the dial pulse signal.

The operation of the polarity reversal detection circuit of the present invention in which the electronic sink circuit 21 and the dial pulse sending circuit 31 are connected will be described.

Generally, in a button telephone device, etc., the device is connected and operates without knowing the polarity connected to Ll and Lz, but in the present invention, when a private branch exchange PBX etc. is connected to a central office line, L1 ．． This circuit is suitable on the assumption that the polarity connected to Lz is known in advance.

■ Normally In this state, the contact S of the switching relay S is turned on (the state shown in the figure) in response to the loop formation signal so as to form a transmission loop.

Since L and L2 are ■, no current flows through PCl.

Also, since diode D2 has reverse polarity, (D
No current flows through the route z -Ra -P C+ (DI). That is, the existence of the polarity reversal detection circuit can be ignored from the viewpoint of Ll and Lz.

(2) At the time of polarity reversal, the contact S1 is on at the same time as in the normal state (the state shown in the figure).

Current flows to CL+-PC+-R4=Dz-L2) and PC
, the light emitting diodes emit light and output polarity reversal information to the OUT terminal. However, since current flows through this loop, AC loss occurs, but since R4 can be made sufficiently larger than 600Ω, this loss is small and can be easily compensated for with an electronic circuit.

Furthermore, since the photocoupler PCI does not enter the DC loop in series during normal polarity reversal, we implemented an electronic synchro path in the latter stage that satisfies the DC resistance limit condition (50 to 300Ω) seen from L, L2. It can be easily configured as shown in the example.

The diode D1 in the figure is added for the purpose of protection when the reverse breakdown voltage of the photocoupler Pct is small, and when the DI is not required, the diode D2 can also be deleted. Also, regarding the dial sending circuit 3, the diode bridge 1 in the figure
It does not matter where it is located on the route between the transformer T1 and the transformer T1.

(Effects of the Invention) As explained above, according to the present invention, since the current on the light emitting diode side of the photocoupler can be reduced, it is possible to configure a polarity reversal detection circuit using an inexpensive photocoupler. A compact office line interface can be provided as a whole. Furthermore, there is an advantage that the DC impedance of L+ and Lz is not affected.

In particular, the present invention is suitable for, for example, a private branch exchange (PBX) where the polarities of L + and L z are known in advance.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a conventional polarity reversal detection circuit;
The figure is a circuit diagram showing an example of a conventional polarity reversal detection circuit, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. T, T,...transformer, D1-D,...diode, Q1-Q,...transistor, PC, ~PC
3... Photocoupler, R, R, ~R7... Resistor,
DESCRIPTION OF SYMBOLS 1...Diode bridge, 2.21...Electronic circuit, 3,31...Dial pulse output path, RA...Incoming call detection circuit, SW...Call path switch, position, - Place, l...terminal telephone.

Claims (2)

[Claims] (1) A series circuit in which a photocoupler path and a resistor are connected in series is connected between the office lines when forming a DC loop with a predetermined polarity to the polarity of the office line during standby, and dial pulses are generated. A polarity reversal detection circuit configured to have extremely high DC impedance in the series circuit at the time of transmission and to be activated at the time of polarity reversal to extract polarity reversal detection information from the photocoupler path. (2) the photocoupler path is a series path in which the light emitting side of the photocoupler and the diode are connected in series with the same polarity;
2. A polarity reversal detection circuit according to claim 1, comprising a light receiving side of a photocoupler coupled to a light emitting side of said photocoupler.