JPH0368619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surge voltage limiting circuit for protecting equipment from overvoltages such as lightning surges.

Conventionally, discharge type arresters have been used as lightning surge protection elements. However, because discharge-type lightning arresters have variations in discharge voltage, high-voltage lateral surges may occur between the lines, and electronic devices may be destroyed or malfunction due to lateral surges. It becomes a problem. Therefore, in order to absorb the lateral surge, the present inventors previously invented a protection circuit whose main components are a diode bridge, a voltage limiting element, and a thyristor (Japanese Patent Application No. 55-086499).

FIG. 1 shows an embodiment of the invention. In the figure, 1-1 to 1-4 are lines, 2-1 and 2-2 are discharge type lightning arresters, 3-1 and 3-2 are diode bridges, 4 is a voltage limiting element such as a varistor, 5 is a thyristor, 6, 7, 8 are capacitors, 9 is a constant voltage diode, 10 is a resistor, 11 is a communication device, 12
is a voltage limiting circuit. The operating principle will be briefly explained. The horizontal surge that occurs between any lines is 3-1, 3
The polarity is made constant at -2 and applied to the voltage limiting circuit 12. In the voltage limiting circuit 12, when a lateral surge is applied, the capacitor 6 first slightly slows the rise of the surge waveform, and the voltage increases to the operating voltage of the voltage limiting element 4. Here, the capacitor 6 has a small capacitance that does not affect the signal. When the voltage limiting element 4 operates, the rise of the waveform is greatly blunted by the capacitor 7 having a large capacitance, and the voltage rises to the sum of the operating voltage of the voltage limiting element 4 and the operating voltage of the constant voltage diode 9. Here, when the constant voltage diode 9 operates, a current flows into the capacitor 8, and when this current is larger than the gate trigger current of the thyristor 5, the thyristor 5 is fired, and the surge voltage is reduced to the operating voltage of the voltage limiting element 4. do. FIG. 2 shows an example of a surge absorption waveform. In the figure, 13 is an applied surge waveform, 14 is a surge absorption waveform, V _VR is the operating voltage of the voltage limiting element 4, and VZD is,
This is the operating voltage of the constant voltage diode 9.

In this circuit, a capacitor 7 with a large capacitance is used to slow down the rise of the waveform, so in the case of a high voltage surge where the waveform rises quickly,
The current flowing through the voltage limiting element 4 before the constant voltage diode 9 operates may become as large as several tens of amperes. On the other hand, voltage limiting elements such as varistors and voltage regulator diodes have differential resistance in their operating region, so
The operating voltage of the voltage limiting element 4 increases due to the current flowing through the capacitor 7. Figure 3 shows
A typical example is the operating resistance of a varistor.
When the operating voltage of the voltage limiting element 4 increases, the voltage limiting circuit 12 when the constant voltage diode 9 operates
The voltage will also increase. The broken line in Figure 4 is
It shows the maximum limiting voltage characteristics of the voltage limiting circuit 12 with respect to the applied surge voltage. It can be seen that as the applied surge voltage increases, that is, as the surge rises faster, the current flowing through the capacitor 7 increases, and the maximum limit voltage also increases accordingly.

The reason for this is that the circuit of the capacitor 7 that slows the rise of the waveform and the gate circuit of the thyristor consisting of the constant voltage diode 9 and the capacitor 8 are both connected to the voltage limiting element 4.
When the operating voltage of the voltage limiting element 4 rises due to the current flowing through the voltage limiting element 4, the operation of the voltage regulator diode 9 is delayed by the amount of the rise.

The present invention separately configures a circuit including a capacitor in series that blunts the rise of a surge and a circuit that supplies a trigger current to the gate of a thyristor, and connects them in parallel to create a rise steepness suppression circuit. Even if the flowing current changes, the gate trigger current is supplied to the SILSTAR gate circuit at a substantially constant voltage, so that a low and stable maximum limit voltage characteristic can be obtained.

FIG. 5 is an embodiment of the present invention. In the figure, 4 is a first voltage limiting element, and a varistor or the like having a large surge current resistance is used. The operating voltage of No. 4 is slightly higher than the telephone's DC voltage of 48V. 5 is a thyristor. 4 and 5 constitute the main surge absorption circuit. 34 is a constant voltage diode which is a second voltage limiting element, and its operating voltage is slightly higher than about 140V, which is the telephone howler signal tone voltage. 8 is a capacitor of about 0.1μF. The series circuit of 34 and 8 forms the thyristor gate firing circuit. Further, 32 is a constant voltage diode whose operating voltage slightly exceeds 250V, which is the insulation test voltage for telephones, and constitutes another gate ignition circuit. Reference numeral 15 denotes a constant voltage diode whose operating voltage is slightly higher than 48V in terms of telephone direct current voltage.
16 is a capacitor of about 0.5μF. 15 and 1
6 constitutes a surge voltage rise steepness limiting circuit. 17 is a capacitor with a small capacitance, 36 is a resistor for discharging the charge of the capacitor 16 when the thyristor 5 is fired, 37 is a resistor for discharging the charge of the capacitor 8, and 38 is a constant voltage diode 34. This diode prevents displacement current from flowing through capacitor 8 before operation, and blocks current from flowing from 4 to 8 when varistor 4 operates. 18 is a resistor for discharging the charges in the capacitors 8 and 16 when the thyristor 5 does not operate, and has a resistance value of 1 MΩ or more so as not to affect the insulation test of the telephone.

Prior to a detailed explanation of the circuit operation, the aim of this embodiment will be described. As mentioned above, the present invention is a circuit mainly for protecting computerized electronic equipment from overvoltages such as lightning surges. Since electronic equipment is easily damaged by overvoltage, it is desirable to limit voltages other than signal voltages used in telephones to as low a voltage as possible. Telephones have the following signals, as is conventionally known:

Call signal: Voltage 48V or less, frequency several kHz.

Howrah signal: Voltage is 140V, frequency is 400Hz.

Line insulation test voltage: Voltage is 250V, applied as direct current, and resistance value of 1MΩ or more is required.

On the other hand, surges that enter the line are typified by lightning surges, and the voltage is several kV and the time is several μs to 1 ms (approximately 1000 Hz or more in terms of frequency). Therefore,
The goal for a circuit that absorbs only surges without affecting the signal is to use 140V if possible for voltages over 400Hz.
It must operate at a voltage that is higher than that and as low as possible, and at least a voltage that slightly exceeds 250V.

For direct current, do not operate below 250V.

It is. The fact that this embodiment satisfies this condition will be described below in comparison with a conventional circuit (FIG. 1).

In FIG. 5, the main parts of the invention are 4 and 5.
and a thyristor gate circuit consisting of a constant voltage diode 34 and a capacitor 8. In the conventional circuit shown in FIG. 1, a gate circuit is constituted by a series circuit of a varistor 4, a constant voltage diode 9, and a capacitor 8.

The operation is described below. In FIG. 5, since the gate circuit includes a capacitor in series, even if a direct current is applied to both ends of the surge absorption circuit, the thyristor 5 does not operate and the circuit is non-conductive. Therefore,
There is no problem with the above 250V insulation test. On the other hand, when a surge is applied, a displacement current flows through the capacitor 8, so if this current is equal to or higher than the gate-on current of the thyristor, the thyristor becomes conductive. As is well known in the art, the turn-on time of a thyristor depends on the gate current. That is, the larger the gate current is, the faster it turns on. Since it is desirable for surge absorbing thyristors to operate at high speed, the gate current is relatively high. In the case of this example, 100mA
A certain amount of current is required. When a surge is applied, how this gate-on current can be supplied with as little delay time as possible is an important factor that determines the characteristics of the surge absorption circuit.

In this embodiment, the gate circuit uses a constant voltage diode 34 and a capacitor 8. A constant voltage diode has a small surge current capability, but has the advantage of a low impedance near the operating voltage. Specifically, in the case of a constant voltage diode with an operating voltage of about 140V, the voltage drop due to a current of about 100mA is a few volts.
It is. Therefore, when the surge voltage slightly exceeds 140V, sufficient current quickly flows through the gate of the thyristor. After a short delay time the thyristor fires. When the thyristor fires, the main surge absorption circuit operates, so the surge current is absorbed by the varistor 4.
and passes through thyristor 5. Therefore, the surge voltage is limited to the voltage of the varistor 4. As shown in FIG. 3, the varistor 4 has the disadvantage of high surge impedance near the operating voltage, but has the advantage of being able to flow a large current due to its high surge current resistance. If you choose a varistor that operates at a voltage slightly over 48V (for example, 70 to 80V), the voltage drop when a surge current of about 100A flows will be 140 to 160V, which is about twice as much as shown in Figure 3. . As described above, according to this embodiment, the main surge absorption circuit operates at a voltage slightly exceeding 140V, and limits the surge voltage to about 160V or less.

On the other hand, in the conventional circuit shown in FIG. 1, a varistor 4 constituting a main surge circuit is used in the gate circuit. That is, 4 and 9 must operate in order to fire the thyristor. The varistor 4 is shown in FIG. 3, and has the drawback of high impedance near the operating voltage as described above. Therefore,
While the 100 mA current necessary for thyristor operation flows, the voltage of the varistor increases by several tens of meters as shown in Figure 3.
%Rise. Furthermore, during the delay time until the thyristor fires, the voltage across the varistor further increases. In this way, as the surge voltage increases, that is, as the rise of the waveform becomes steeper, the absorbed voltage increases as shown by the broken line in FIG. 4.

Next, the functions of the circuit configuration of this embodiment shown in FIG. 5 will be explained using FIG. 6. Figure 6 is the 5th
This figure shows a surge absorption waveform due to the operation of the circuit shown in the figure (Figure 6 shows the case where the surge current is about 50A). In FIG. 6, 13 is a surge voltage. When a surge is applied, capacitors 17 and 1 are first
The series circuit of 6 operates and makes the waveform a little dull. The surge voltage is the operating voltage of the voltage regulator diode 15 (48V
When the voltage slightly exceeds 100 Ω, the series circuit of the constant voltage diode 15 and the capacitor 16 with a large capacitance operates, greatly dulling the waveform. When the voltage increases further and the constant voltage diode 34 operates at a voltage slightly above 140V, current flows through the gate of the thyristor and after a short delay time the thyristor 5 operates. When the thyristor 5 operates, a surge current flows through the varistor 4. Surge current is 50A
As shown in FIG. 3, the limiting voltage is about 1.5 times the operating voltage of the varistor. That is, the operating voltage
The limiting voltage using a 70-80V varistor is
It drops to about 120V. In Figure 3, it is the voltage of V _VRZ .
Further, when the silis becomes conductive, the electric charge charged in the capacitor 8 is discharged through the paths 38, 37, and 5. Furthermore, the electric charge charged in the capacitor 16 is 1
It is discharged along the route 5, 4, 5. When the surge subsides, the only voltage applied to the circuit is the telephone's DC voltage. In other words, the voltage is about 48V, so varistor 4
is turned off. Therefore, no current flows through the thyristor 5, and the thyristor also returns to its off state.

In the circuit of FIG. 5, 32 is a constant voltage diode that operates at a voltage slightly over 250V.
This circuit is for activating the circuit and protecting the computerized electronic equipment, for example, when a direct current overvoltage other than a surge is applied to the telephone circuit.

In the present invention, the second voltage limiting element is not limited to one constant voltage diode, and a plurality of constant voltage diodes may be connected in series. FIG. 7 shows such an embodiment. In Figure 7, 9
is a constant voltage diode. The operating voltage of 9 is 15
Set the operating voltage of the series circuit of and 9 to slightly exceed 140V. That is, the constant voltage diode 15
Assuming that the operating voltage of is about 60V, the voltage regulator diode 9 is set to operate at about 80V. The gate circuit is composed of a series circuit of 15, 30, 31, 33, 9, and 8. Since the operation is similar to that shown in FIG. 5, it will be briefly explained. First, when a surge is added, 1
The series circuit of 5 and 16 operates to dull the waveform. Next, when the voltage slightly exceeds 140V, the gate circuit described above is activated, the thyristor becomes conductive, and the voltage becomes the varistor limit voltage.

According to the present invention, the rise of a surge can be blunted with a low voltage, and even if the applied surge voltage increases, the maximum limiting voltage can be kept low, so a low voltage is necessary to limit the surge voltage.
When applied to communication equipment that uses a PNPN switch, it is effective in improving reliability.

[Brief explanation of drawings]

Figure 1 shows the conventional surge protection circuit, Figure 2 shows the 1st surge protection circuit.
Figure 3 shows the surge absorption waveform, and Figure 3 shows the varistor voltage and
4 shows the maximum limiting voltage characteristic, FIG. 5 shows an embodiment of the present invention, FIG. 6 shows the surge absorption waveform of FIG. 5, and FIG. 7 shows another embodiment of the present invention. 1-1 to 1-4...Railway, 2-1, 2-2...
Discharge type lightning arrester, 3-1, 3-2... diode bridge, 4... voltage limiting element (varistor), 5...
...Thyristor, 6,7,8,16,17...Capacitor, 9,15,32,34...Voltage limiting element (constant voltage diode), 10,18,30,33,
36, 37...Resistor, 11...Communication device, 12...
...Voltage limiting circuit, 13... Applied surge waveform, 14
... Surge absorption waveform, 31, 35, 38... Diode.

Claims (1)

[Claims] 1 A surge absorption circuit comprising a main surge absorption circuit consisting of a first voltage limiting element 4 and a thyristor 5 connected in series to the element, and an ignition circuit for the thyristor, wherein the ignition circuit is , the ignition circuit has a series circuit including a second voltage limiting element 34 whose operation start voltage is higher than the limiting voltage of the first voltage limiting element and a capacitor 8, and one end of the ignition circuit is connected to the first voltage limiting element. A surge voltage limiting circuit characterized in that the voltage limiting element is connected to a terminal on the side to which the thyristor is not connected, and the other end is connected to the gate terminal of the thyristor.