JPS646614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lateral surge absorption circuit for telephone equipment using a plurality of paired communication lines.

Conventionally, in devices such as button telephones that use multiple communication lines, in order to protect the device from vertical surges, overvoltage absorption elements are used between each line and the ground to absorb vertical surges, as shown in Figure 1. . In the figure, 5, 6, 7, and 8 are two-terminal overvoltage absorbing elements, one end of which is connected to each line, and the other end is connected in common, and 9 and 10 are three-terminal overvoltage absorbing elements, respectively. It has the characteristic of integrating 5 and 6, 7 and 8. There are two types of overvoltage absorbing elements: those that utilize electrical discharge, such as carbon lightning arresters and detonators, and those that use overvoltage limiting elements that operate at a constant voltage, but no matter which one is used, devices that use multiple pairs of communication lines will suffer from lightning surges. When an intrusion occurs, a high voltage called a lateral surge is generated between each line. The lateral surge generation mechanism will be explained.

FIG. 2 is a diagram showing a lateral surge generation mechanism when a lightning arrester that utilizes discharge is used as an overvoltage absorbing element. Lightning arresters for telephones that use electrical discharge are
Since the starting voltage for discharge varies considerably from 600 to 1000V, even if a surge enters each line in the same phase, the discharge start time may be delayed as shown in ○A and ○B, or as shown in ○C. Sometimes there is no discharge, and this causes lateral surges like ○D and ○E. ○D is a lateral surge that occurs between ○A and ○Ro, and ○Ho is a lateral surge that occurs between ○Ro and ○C. Furthermore, when a surge with a different phase enters, the delay in the discharge start time is further increased, and a lateral surge is more likely to occur. Since these lateral surges are caused by discharge, the rise of the waveform is extremely fast, sometimes less than 0.1 μsec. Also, the voltage depends on how quickly the vertical surge rises, but the maximum
It can reach up to 1000V, and the duration of the lateral surge is the longest in the case of ○ and can be up to about 200μsec. Moreover, this lateral surge appears between arbitrary lines 1, 2, 3, and 4 when a 2-pole arrester is used, and mainly appears between A and B when a 3-pole arrester is used.

FIG. 3 is a diagram showing a lateral surge generation mechanism when an overvoltage limiting element that operates at a constant voltage is used as an overvoltage absorbing element. Overvoltage limiting elements include semiconductor varistors and constant voltage diodes, which operate extremely quickly and have little variation, so lateral surges are less likely to occur in response to same-phase surges.
Since the communication lines L ₁ and L ₂ are always routed along the same route from the station to the subscriber, surges that enter these lines are considered to be in the same phase, and when an overvoltage limiting element is used, the surges between these lines are The surge is small. However, in devices that use multiple communication lines, these lines are not necessarily routed along the same route from the station to the subscriber, and may take different routes. Surges with different phases and voltages may enter. In this case,
Even if the overvoltage limiting element operates to limit the voltage of the vertical surge to the limiting voltage of the element as shown in ○, a horizontal surge as shown in ○ is generated between the paired communication lines. The maximum value of horizontal surge occurs when a vertical surge of opposite polarity to the ground enters the communication line, and in this case, a maximum voltage of about 1000V, which is twice the limiting voltage of the element, is applied. There is.

As described above, in telephone equipment that uses multiple communication lines, no matter what kind of conventional vertical surge absorption circuit is used, horizontal surges occur between each line.
This voltage is particularly high between the communication lines, reaching a maximum of 1000V, with a minimum rise time of 0.1μsec or less, and a surge duration of up to 200μsec.

Additionally, in devices that use multiple communication lines, there is a trend toward electronic switches for switching communication paths, but the withstand voltage of the semiconductor elements used at the crossing points is high.
Since the voltage is approximately 500V, there is a risk that the switch will be destroyed if such a high voltage as mentioned above is applied to the crossing point. Furthermore, if this communication path switch is constructed of PNPN elements, there is a risk that a lateral surge that rises quickly will cause malfunction or destruction of the PNPN elements due to their dv/dt tolerance being exceeded. Therefore, in devices using electronic communications channels, a surge absorption circuit that efficiently absorbs lateral surges is important.

The present invention protects the circuits of communication devices by limiting the lateral surge voltage and limiting the rising speed.
The present invention provides a lateral surge absorption circuit that can prevent malfunction and destruction of a PNPN switch.

The present invention will be explained in detail below using the drawings.

FIG. 4 shows an embodiment of the present invention, which is a lateral surge absorption circuit for a device using two paired communication lines. In the figure, 11 and 12 are diode blocks for rectification;
1-1, 2, 12-1, 2 are rectified wave input terminals,
11-3, 4, 12-3, 4 are rectified output terminals, 1
3 is an overvoltage absorption circuit. The operating principle of this circuit will be explained. A lateral surge may occur between any of the lines 1, 2, 3, and 4, but any lateral surge is applied between two terminals of the overvoltage absorption circuit 13. This is due to the following reason. For example, the lateral surge that occurs between communication lines 1 and 2 is [1→11(1)→11(3)→
13→11(4)→11(2)→2] is applied to the circuit,
The lateral surge that occurs between 1 and 3 is [1→11(1)
→11(3)→13→12(4)→12(1)→3], and the lateral surge generated between other lines is also applied to the series circuit of two forward diodes and overvoltage absorption circuit 13. However, since the forward voltage drop of the diode is small, most of the voltage of the lateral surge is applied between the two terminals of the overvoltage absorption circuit 13. Therefore,
If the overvoltage absorption circuit 13 is an overvoltage absorption circuit that does not operate on telephone signals but has the characteristic of operating against surges, the overvoltage absorption circuit 13 can absorb all horizontal surges between arbitrary lines. Further, since voltage is applied to the overvoltage absorption circuit 13 only in one direction, a unidirectional absorption circuit can also be used. Here, the overvoltage absorption circuit includes a lightning arrester that uses discharge, such as a two-pole lightning arrester or a carbon lightning arrester, an overvoltage limiting element that operates at a constant voltage, such as a semiconductor varistor or a constant voltage diode, and a switching element such as a thyristor or Schottley diode. , etc. can be used.

FIG. 5 is a diagram in which the horizontal surge absorption circuit of the present invention is connected to the vertical surge absorption circuit of FIG. 1. In the circuit shown in FIG. 5, vertical surges are absorbed by circuits 5, 6, 7, 8 or 9, 10, and horizontal surges are absorbed by overvoltage absorption circuit 13.

Each circuit in FIGS. 6 to 15 is an overvoltage absorption circuit 13.
This is a specific example with the following characteristics.

Figure 6 shows an overvoltage limiting element 14 that operates at a constant voltage.
This is a circuit in which an overvoltage absorbing element 15 is connected in series with this. The characteristics of this circuit will be explained. The voltages used in telephones are mainly approximately 48V DC voltage with a 4KHz voice signal superimposed, AC voltage with an effective value of 75V at 16Hz used for bell signals, and approximately 250V DC voltage used for equipment insulation tests. It is.
The circuit of FIG. 6 must not operate on or affect these signals. If the overvoltage limiting element 14 is one that operates at a voltage higher than the DC voltage of approximately 48 V plus the amplitude of the audio signal, the circuit shown in Fig. 6 will not operate without the overvoltage absorbing element 15, and the overvoltage will be reduced. Since the limiting element 14 has a small capacitance in an inactive state, it does not affect the audio signal. Therefore, the overvoltage absorbing element 15 is designed to operate at as low a voltage as possible without affecting the bell signal, and by paying attention to the condition that it does not operate at a DC voltage of 250V DC minus the operating voltage of the overvoltage limiting element 14. Can design circuits. Note that since the circuit shown in FIG. 6 has fixed polarity, it is also possible to use an element with a single polarity as the overvoltage limiting element 14.

FIG. 7 is an example of a circuit using a semiconductor varistor 16, which is an example of a bipolar overvoltage limiting element, as the overvoltage limiting element 14, and FIG. 8 is an example of a circuit using a constant voltage diode 17, which is an example of a unipolar overvoltage limiting element. It is.

In FIG. 9, a parallel circuit of a capacitor 18 and an overvoltage absorbing element 19 is used as the overvoltage absorbing element 15. As 19, a semiconductor switching element such as a thyristor or a Schottley diode, or an overvoltage limiting element such as a varistor or a constant voltage diode can be used. The effect of the capacitor 18 will be explained. As mentioned above, the rise speed of the lateral surge is
There are some that are quite fast, less than 0.1μsec. If such a surge is applied to the circuit shown in Figure 9,
If 19 is composed of an overvoltage absorbing element such as a thyristor or a Shockley diode that operates when the withstand voltage is exceeded, which causes a time delay of about 0.5 to 1 μsec between the time a surge enters and the time it operates,
High voltage may be generated during this delay time, which may have an adverse effect. The capacitor 18 delays the rise of the lateral surge by its capacitance and the time constant of the line resistance, and
This prevents the generation of high voltage due to the time delay in the operation of step 9. Capacitor 18 can be used with a capacitance of up to 3μF under the condition that it does not affect the 16Hz bell signal, but the line resistance must be at least
Since it is expected to be 10Ω or more, this time constant is several tens of microseconds.
Therefore, it is possible to completely compensate for the maximum operating time delay of about 1 μsec in No. 19. Also, slowing down this rise is extremely effective in preventing malfunctions due to exceeding the dv/dt tolerance of the PNPN switch in equipment that uses a PNPN switch in the communication path. In the circuit of FIG. 9, 29 indicated by a broken line is a resistor. If charge remains in the capacitor 18 even after the surge has subsided, the capacitor 18 may become inoperable when the next surge occurs. The resistor 29 is used to discharge the charge remaining in the capacitor 18 after the surge has subsided, and is a high resistor that does not affect the bell signal. This resistor 29 is particularly effective when lightning surges occur in a short period of time.

In Figure 10, 19 is replaced with a Schottley diode 20.
This is an example of a circuit when using .

FIG. 11 is an example of an overvoltage absorbing circuit using a thyristor in 19. FIG. The advantage of using a thyristor is that the thyristor operates at a low voltage when current is passed through its gate, so if you add a drive circuit that drives the thyristor only when a surge enters, the circuit shown in Figure 11 can reduce the lateral surge to the surge of the overvoltage limiting element 14. The ability to limit the voltage to slightly more than 100V when current is applied is possible. Further, since the thyristor is a unidirectional element, it is suitable for the overvoltage absorbing element 19. In the figure, 21 is a thyristor, 22 is a capacitor, 2
A resistor 3 drives the thyristor 21 by means of 22 and 23. The operating principle will be explained. The frequency component of the lateral surge is at least 1 kHz or more even when the waveform is sufficiently blunted by the capacitor 18, which is nearly two orders of magnitude higher than that of the bell signal. Therefore, the impedance of the capacitance of the capacitor 22 for the bell signal is at least two orders of magnitude higher than for the surge.
Therefore, in the case of a bell signal, the voltage drop between the gate and cathode is minute, but when a surge enters, the capacitor 22's capacitance and resistance are A value of 23 can be selected, in which case the lateral surge can be quickly absorbed without affecting the bell signal. Further, since a general thyristor can easily achieve both a forward blocking voltage and a reverse breakdown voltage of 300 V or more, the circuit shown in FIG. 11 will not operate in an insulation test with 250 V DC applied, and there will be no problem with the test.

In the circuit shown in FIG. 12, the resistor 23 is replaced with a constant voltage diode 24 to prevent the voltage between the gate and the cathode from exceeding a certain value when a surge occurs.

FIG. 13 shows another embodiment of the overvoltage absorbing circuit, in which an overvoltage absorbing element 25 having a higher operating voltage than the overvoltage limiting element 14 is connected in parallel to the series circuit of the overvoltage limiting element 14 and the capacitor 18. In this circuit, overvoltage limiting element 14 and capacitor 18
The series circuit 25 operates only when a horizontal surge enters and delays the rise of the waveform, but after that, the circuit 25 starts operating and mainly absorbs the surge. Therefore, it is possible to use an overvoltage limiting element 14 having a relatively small withstand capacity. Each of the circuits shown in FIGS. 14, 15, and 16 uses a semiconductor varistor 26, a constant voltage diode 27, and a bipolar detonator 28 as 25, respectively.

The present invention is efficient and economical since all lateral surges occurring between multiple communication lines can be absorbed by one lightning arrester or one surge absorption circuit.The rise of the waveform of lateral surges occurring between lines Its advantages include that it can be absorbed quickly at a low voltage after slowing down the voltage, and that it has almost no effect on telephone signals and insulation tests even when connected to telephone equipment. It is highly effective for application to key telephones, electronic exchanges, line concentrators, etc. that use PNPN communication path switches, which are difficult to withstand.

Further, in the description of the surge absorption circuit of the present invention, the main subject is telephone equipment, but the concept can be similarly applied to other equipment such as data equipment.

Furthermore, although the present invention uses a diode bridge for each pair of communication lines, this circuit connects one pole of a pair of diodes with opposite polarities to the communication line for each communication line. However, since the other ends of the diodes are connected together for each polarity, this idea can be applied not only to devices that use an even number of communication lines but also to devices that use an odd number of communication lines. . As an example, FIG. 17 shows an example of a lateral surge absorption circuit for a device using three communication lines. In this case, apparently 1 and 2,
1 and 3 and 2 and 3 are paired communication lines.

Note that in addition to the paired communication line explained above, a grounding line is sometimes used in practice, but for lines that do not generate surges or only generate low-voltage surges, the addition of a diode bridge can be omitted. , may be excluded from application of the present invention.

[Brief explanation of drawings]

Fig. 1 is a connection system diagram showing an example of a vertical surge absorption circuit of a conventional device using multiple paired communication lines, Fig. 2 is a waveform diagram showing a lateral surge generation mechanism when a lightning arrester using discharge is used, Fig. 3 is a waveform diagram showing the lateral surge generation mechanism when using an overvoltage limiting element that operates at a constant voltage, Fig. 4 is a circuit diagram showing an embodiment of the present invention, and Fig. 5 is a usage example of the present invention. Circuit diagram shown,
6 to 16 are block diagrams or circuit diagrams showing specific examples of the overvoltage absorbing circuit used in the present invention, and FIG. 17 is a circuit diagram showing another embodiment of the present invention. 1 to 4...Communication line, A...Pair communication line consisting of 1, _L1 , 2, _L2 , B...Pair communication line consisting of 3, _L1 , 4, _L2 , 5 to 8...2 Terminal overvoltage absorbing element, 9, 10...3 terminal overvoltage absorbing element, 1
1, 12... Rectifier diode bridge, 11-
1, 2, 12-1, 2... Rectified wave input terminal, 1
1-3, 4, 12-3, 4... Rectifier output terminal, 1
3... Overvoltage absorption circuit, 14... Overvoltage limiting element that operates at constant voltage, 15... Overvoltage absorption element, 1
6... Semiconductor varistor, 17... Constant voltage diode, 18... Capacitor, 19... Overvoltage absorption element, 20... Shockley diode, 21...
Thyristor, 22... Capacitor, 23... Resistor, 24... Constant voltage diode, 25... Overvoltage absorption element, 26... Semiconductor varistor, 27... Constant voltage diode, 28... 2-pole detonator, 29...
resistance.

Claims (1)

[Claims] 1. In a device using a plurality of pair communication lines, each pair communication line is connected to a rectified wave input terminal of a rectifying diode bridge, and each diode bridge has a common rectified output terminal. A lateral surge absorption circuit characterized in that the overvoltage absorption circuit is configured to be connected between two terminals. 2. The lateral surge absorption circuit according to claim 1, wherein the overvoltage absorption circuit is a circuit in which an overvoltage absorption element is connected in series with an overvoltage limiting element that operates at a constant voltage. 3. The lateral surge absorption according to claim 1, wherein the overvoltage absorption circuit is a circuit in which a parallel circuit of at least a capacitor and an overvoltage absorption element is connected in series with an overvoltage limiting element that operates at a constant voltage. circuit. 4. The lateral surge absorption circuit according to claim 3, wherein the parallel circuit includes a resistor connected in parallel to a capacitor. 5 A thyristor is used as the overvoltage absorbing element connected in parallel to the capacitor, and a capacitor is connected between the anode and the gate as the drive circuit, and a resistor or a constant voltage diode is connected between the gate and the cathode, and only when a surge enters. 5. The lateral surge absorption circuit according to claim 3, wherein the overvoltage absorption circuit is configured such that a voltage for driving the thyristor is applied between the gate and the cathode. 6. The overvoltage absorption circuit according to claim 1, wherein the overvoltage absorption circuit is a circuit in which an overvoltage absorption element is connected in parallel to a circuit in which at least a capacitor is connected in series with an overvoltage limiting element that operates at a constant voltage. Lateral surge absorption circuit. 7. The lateral surge absorption circuit according to claim 6, wherein a resistor is connected in parallel to the capacitor.