JPS5829700B2 - Communication safety circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a circuit configuration of a communication protector.

In order to expand the functionality and reduce the cost of semiconductor components, semiconductor integrated circuits with low surge resistance are being widely introduced into communication devices such as telephones and telephone exchanges.

In order to protect these semiconductor integrated circuits with low surge resistance from lightning surges, various protectors have been used.

FIG. 1 shows the basic configuration of a conventional safety device.

In the figure, LA and LB are the line side terminals of the protector, ZlA and Zl
B is the primary arrester, ZSA IZSB is the series impedance that improves surge suppression characteristics, Z2A and Z2B are 2
Next is the arrester and then the SA.

SB is a terminal on the protected element side.

FIG. 2 shows a typical circuit configuration of the protector shown in FIG.

I.A. 1B is a gas gap type arrester that absorbs most of the energy of lightning surges that enter between the line side terminal and the ground, and releases it to the ground.

However, this gas gap arrester IA.

Since 1B alone has a discharge delay time of several microseconds to several tens of microseconds, for example, even if the DC discharge starting voltage is selected as 160V, a peak voltage of about 300 to 100OV will be applied to the line ground during the discharge delay time. remain in between.

On the other hand, the surge voltage withstand capacity of the protected element is often at most 200 µm or less, and therefore it is necessary to further lower the surge voltage limiting characteristics.

For this reason, the inserted element has a series impedance Zs as shown in the figure.
and secondary arrester 2A.

It is 2B.

This series impedance Zs is constituted by a common mode choke coil that exhibits a very low impedance against a line loop signal, but a high impedance against a surge voltage between the line and the earth, that is, a lightning surge.

In addition, the secondary arresters 2A and 2B are voltage nonlinear elements such as zinc oxide sintered type, and the rising voltage of the voltage-current characteristics is determined by the surge resistance of the protected element and the voltage level of the line loop signal. .

FIG. 3 shows the circuitry of the protector shown in FIG.

L is the inductance of the common mode choke coil, C
is the capacitance between the electrodes of a voltage nonlinear element such as a sintered zinc oxide type, r is approximately outside the effective resistance of the common mode choke coil, and Sw is the capacitance between the electrodes of a voltage nonlinear element such as a zinc oxide sintered type, and Sw is the capacitance between the electrodes of a voltage nonlinear element such as a zinc oxide sintered type, This is a switch that means that the mold electrodes are almost in a short-circuited state.

In the circuit shown in Figure 3, if we consider the case where a lightning surge is applied between terminals L and E, the input lightning surge will be r - L because the switch Sw is open during the discharge delay time.
Since it is directly applied to the series circuit of -C, energy is stored in the form of current and voltage in L and C, respectively.

When the lightning surge reaches the discharge starting voltage of the gas gap type arrester, it enters a discharge state, and in the equivalent circuit of FIG. 3, the switch SW changes to the closed state.

At this time, the switch SW is closed while energy is stored in C, so the output voltage Eo is caused by L-C resonance.
begins to vibrate.

On the other hand, zinc oxide sintered voltage nonlinear elements have large voltage nonlinear coefficients and surge resistance, and have symmetrical characteristics with respect to positive and negative surges, so they have recently been particularly used as surge absorption elements. It is characterized by a very large interelectrode capacitance.

- For example, an element with external dimensions of a circular plate shape with a diameter of 15mm and a rising voltage of 150V in voltage-current characteristics is approximately 1400P.
It is F.

Furthermore, the effective resistance molecule of the resonant loop, represented by the effective resistance of the common mode choke coil, is often as small as about 10 g or less because it is necessary to lower the insertion loss of the protector with respect to the line loop signal.

For this reason, the output voltage of the protector after the start of discharge of the gas cap type arrester fluctuates greatly for a long time, and in experiments, it was observed that the output voltage lasted for as long as 200 microseconds.

An example of the waveform of this output voltage is shown in A (solid line) in FIG.

In FIG. 4, tl is gas gap type arrester IA,
This is the discharge start time of IB, and Tc is approximately.

The period of vibration is determined by the magnitude of C.

As described above, the conventional safety circuit has the disadvantage that the output voltage remains in an oscillating state for a long time, which may adversely affect the protected elements.

Of course, if the series impedance Zs is replaced with a resistor, vibration will not occur, but the insertion loss of the protector increases, which naturally limits its application.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art and to provide a communication safety circuit that quickly converges output voltage oscillations and has significantly low insertion loss.

In the equivalent circuit of FIG. 3, when the switch SW is closed with energy stored in L-C, the oscillating current {circle around (2)} is given by the following equation.

The convergence time of vibration is proportional to the time constant τe.

That is, the larger the equal series resistance r is, the shorter the vibration convergence time is.

The present invention is a communication safety circuit in which a common mode choke coil is inserted as a series impedance element between a primary arrester and a secondary arrester, and a damping resistor is connected in parallel to one of the common mode choke coils. By doing so, the resistance is increased to a certain degree and the above-mentioned drawbacks are eliminated.

The communication security circuit according to the present invention will be explained in detail below with reference to the drawings.

FIG. 5 shows an embodiment of the communication security circuit according to the present invention.

As shown in the figure, two primary arresters are installed between the track and the ground.
Polar gas gap type arresters IA and IB are used as secondary arresters, and voltage non-linear elements 2A and 2B made of zinc oxide as a main ingredient and sintered with impurities added thereto are used as secondary arresters, and as series impedance elements. A common mode choke coil Z is installed between the primary arrester and the secondary arrester.
s is inserted, and a damping resistor Rs is further connected to both ends of at least one coil of this common mode choke coil Zs.

In this circuit configuration, an example of the output voltage waveform when a lightning surge is applied is as shown in FIG. 4 (broken line).

The optimal value of the resistor R8 varies depending on the inductance size of the common mode choke coil Z8, etc., but as an experimental example, the inductance L = of the common mode choke coil
0.5 rn Hs When the interelectrode capacitance C of the voltage nonlinear elements 2A and 2B is set to 1400PF, the vibration convergence time was 220 microseconds without adding the resistor R8, but the resistor R8 = IK, (, / is shortened to 24 microseconds.

This is because the energy loss of the resonant circuit increases due to the addition of the resistor R8, and the vibration convergence time becomes faster.

Further, in this case, no increase in the peak value of the output voltage due to the addition of the resistor R8 was observed.

This shows that the effect of series impedance on lightning surges is not lost.

Note that the above effect occurs only in the attenuation characteristics of the lightning surge applied between the line and the earth, and the fact that the attenuation characteristics of the signal loop are not affected by the addition of the resistor Rs is due to the operation of the common mode choke coil. It is clear in principle.

That is, there is no increase in insertion loss for the loop signal due to the addition of the resistor R8.

FIG. 6 shows another embodiment of the present invention, in which the primary arrester is a three-pole gas gap type arrester, and the resistor R8 is added to both sides of the common mode choke coil. The aforementioned effects are not lost.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic configuration of a communication protector, Figure 2 is a conventional communication safety circuit diagram, Figure 3 is an equivalent circuit diagram of Figure 2, and Figure 4 is a conventional safety circuit. FIGS. 5 and 6 are output voltage waveform diagrams of the safety circuit according to the present invention when a lightning surge is applied, and FIGS. 5 and 6 each show a safety circuit diagram of an embodiment of the communication safety circuit according to the present invention. LA, LB: Line side terminals, SA, SB: Protected side terminals, IA, IB: Primary arrester, Zs: Common mode choke coil, 2A, 2B: Secondary arrester, R8: Resistor.

Claims (1)

[Claims] A primary arrester connected between each line on the primary side and the ground air, a secondary arrester connected between each line on the secondary side and the ground air, and a primary side terminal and a secondary side terminal. 1. A communication security circuit comprising a common mode choke coil inserted between the communication security circuits, wherein a resistor is connected in parallel to at least one of the common mode choke coils.