JPH05207647A - Surge absorbing circuit - Google Patents

Abstract

PURPOSE:To provide a surge absorbing circuit which conducts only when a surge voltage is applied. CONSTITUTION:A triac 10 is connected in series with a metal oxide varistor(MOV) 13 wherein the triac 10 is connected, at the gate terminal thereof, in series with Zener diodes 16, 17 and a resistor 18. The Zener diodes 16, 17 are connected in reverse polarities. Upon application of a surge voltage higher than the Zener voltages of the Zener diodes 16, 17, a gate current flows through the triac 10 which is thereby conducted and the surge voltage is applied on the MOV 13. But the MOV 13 is not regulated severity. Power supply voltage is not applied normally onto the MOV 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge absorbing circuit which absorbs a surge voltage to prevent a transient excessive voltage from being applied to a load.

[0002]

2. Description of the Related Art FIG. 10 is a circuit diagram showing a conventional surge absorbing circuit. This surge absorbing circuit is formed by connecting a metal oxide varistor (MOV) 13, which is a polycrystalline sintered body, in parallel with a load. As a required characteristic for MOV, there is required a non-linear characteristic that a leak current is as small as possible at a voltage value that is constantly used, and when a surge voltage is applied, a current flows through the MOV as much as possible to absorb the surge voltage. ..

However, as for the MOV, it is difficult to strictly control the nonlinear characteristics as a property of the polycrystalline sintered body.
If this is demanded too strongly, there is a drawback that the product yield is deteriorated and the MOV is expensive. If a surge of energy more than expected is input, the MO
The power sometimes exceeds the rated power and is deteriorated in characteristics. If the characteristics of the MOV deteriorate, a large leak current flows even with a constant applied voltage value.
There was often a vicious cycle of heat generation and further deterioration, eventually leading to ignition etc. due to self-heating.

To remedy this drawback of MOV, a bidirectional thyristor that does not operate the MOV at the rated voltage and operates the MOV only when a voltage above the rated voltage such as a surge voltage is applied is connected in series to the MOV. Connect to
The circuit is shown in FIG.

The bidirectional thyristor is a bidirectional symmetric switch element having the characteristics shown in FIG. 7, and includes a silicon symmetric switch (SSS), a diac, a sidac,
It is commercially available under the name of Biswitch.

The operation of the bidirectional thyristor will be described in one direction because the two directions are symmetrical. As shown in FIG. 7, when a voltage is applied to both ends of the bidirectional thyristor, it is off until the breakover voltage Vb, but when the applied voltage V exceeds Vb, the bidirectional thyristor is rapidly turned on. The voltage of the bidirectional thyristor when it is on, that is, the on-voltage is about 1V. This on state is turned off when the current I becomes less than or equal to the holding current Ih. Since the bidirectional thyristor operates symmetrically as described above, if the polarities of the voltages at both ends are reversed, the breakover voltage Vb and the holding current Ih are symmetrical operating curves of −Vb and −Ih, respectively. Becomes

A surge absorbing circuit constructed by using a bidirectional thyristor in place of the MOV in the circuit of FIG. 10 is shown in FIG.
Shown in. When surge voltage occurs in the circuit of this figure,
The bidirectional thyristor 12 becomes conductive and the surge voltage is absorbed.

[0008]

As described above, the conventional surge absorbing circuit shown in FIG. 10 has a drawback that it requires a MOV with a strict standard and a low yield, or that MOV characteristic deterioration is likely to occur. The conventional surge absorbing circuit of FIG. 11 eliminates the drawbacks of the circuit of FIG. But,
When the circuit of FIG. 11 receives a surge voltage that rises in a short time of ns or less, it cannot sufficiently absorb the surge voltage of the steep rising portion. The conventional surge absorbing circuit of FIG. 12 also solves the drawbacks of the circuit of FIG. However, in the circuit of FIG. 12, when the bidirectional thyristor 12 becomes conductive, the current flows indefinitely until the power supply voltage drops, and the bidirectional thyristor 1
2 will be destroyed, or the voltage applied to the load 14 will fall.

As described above, in the conventional surge absorbing circuit,
There were issues to be solved in terms of reliability, surge voltage absorption capacity, yield, etc.

[0010]

According to a first aspect of the present invention, a circuit for controlling a gate current by a surge voltage is connected in series with a triac having a gate terminal connected to a metal oxide varistor. Is a surge absorption circuit.

According to a second aspect of the invention, the Zener diode, the resistor and the base of the transistor are connected in series,
It is a surge absorbing circuit for a DC circuit in which a metal oxide varistor is connected in series to the collector of the transistor.

According to a third aspect of the present invention, a first circuit in which two Zener diodes are connected in series in opposite directions to each other and a second circuit in which a bidirectional thyristor and a metal oxide varistor are connected in series are connected in parallel. It is a surge absorption circuit characterized by being connected to.

According to a fourth aspect of the present invention, there is provided a surge absorption circuit for a DC circuit, wherein a zener diode is connected in parallel to a circuit in which a bidirectional thyristor and a metal oxide varistor are connected in series. is there.

According to a fifth aspect of the present invention, a first discharge circuit in which a first diode is connected in series to a parallel connection circuit of a first capacitor and a first resistor, a second capacitor and a second A second discharge circuit in which a second diode is connected in series to the resistance in parallel with the first diode in reverse polarity to the first diode, and a bidirectional thyristor, and the first and second discharge circuits Are connected in parallel, and the two-way thyristor is connected in series at the connection point of these discharge circuits.

[0015]

The present invention will be described in more detail with reference to the following examples.

FIG. 1 is a diagram showing a first embodiment of the invention described in claim 1, and FIG. 2 is a diagram showing the terminals, current and applied voltage of the triac 10 in the circuit of FIG. Figure 1
In order to facilitate the description of this embodiment, the operation of the triac will be described first with reference to FIG.

[0017] When the relative terminal T ₁ to the terminal T ₂ positive voltage is applied, the triac is turned ON when the gate trigger current flows through the G → T _1. Further, when a positive voltage is applied to the terminal T ₁ with respect to the terminal T _2, and the gate trigger current flows from T ₁ → G, the triac is turned on.
The state of ON is OFF if the current I becomes less than the holding current.
become.

The embodiment shown in FIG. 1 will be described. Reference numeral 11 is a power source, which is an AC power source here, but may be a DC power source as shown in FIG. A triac 10 is a switch element, and Zener diodes 16 and 17 and a gate current limiting resistor 18 are connected in series to the gate thereof.
The polarities of the Zener diodes 16 and 17 are opposite to each other. 14 is a load. In the circuit of FIG. 1, the peak off voltage of the triac 10 is set to be equal to or higher than the maximum allowable output voltage of the power supply 11, and the zener diode 1
The Zener voltages of 6 and 17 are set to the suppression voltage values of the applied surge voltage. If only the power supply voltage is applied, the gate current will not flow due to the Zener diode.
Keeps the OFF state. Here, the surge voltage is superimposed on the power supply voltage, and the voltage is applied to the zener diode 16,
If the voltage is equal to or higher than the Zener voltage of 17, the gate current flows through the gate of the triac 10 and the triac 10 is turned on. Since the ON voltage is about 1V, the circuit is M.
OV13 seems to be directly connected to the power supply and absorbs the surge. After that, when the gate current of the triac 10 becomes equal to or lower than the holding current, the triac 10 is turned off, the MOV 13 does not operate at all, and only the leak current of the triac 10 flows in the MOV 13. That is, MOV13
Operates only when a surge voltage is applied and does not normally operate.

FIG. 3 shows a surge absorbing circuit according to a second embodiment of the invention described in claim 1. In this embodiment, a diac 27 is connected instead of the Zener diodes 16 and 17, and a DC power source 15 is used instead of the AC power source 11.
, But its operation is similar to that of the embodiment of FIG.

FIG. 4 is a circuit diagram showing a first embodiment of the invention described in claim 2. In FIG. 4, reference numeral 15 is a DC power supply, and 25 is a Zener diode (ZD), the cathode side of which is connected to the positive side of the DC power supply 15. Two
Reference numeral 0 is a resistor, and 23 is a capacitor, which is connected to the anode side of the ZD 25. Reference numeral 21 is a transistor, MOV 13 is connected to its collector, and 14 is a load. Here, the operating voltage of ZD25 is set to a voltage that matches the absorbed surge voltage, and when no surge voltage is applied, ZD25
The voltage value is set to D25 so that no current flows.

When a surge voltage is applied, the current is ZD2
The flow of 5 → resistor 20 → base of transistor 21 → emitter of transistor 21 makes the transistor 21 conductive, so that the MOV 13 is connected to the power supply 15 and suppresses the surge voltage to protect the load 14. Although the capacitor 23 is not necessary for the basic circuit, the steep rising portion in the surge voltage can suppress the voltage in the circuit of ZD25 → capacitor 23, and the end portion of the surge waveform is charged in the capacitor 23. The electric charge flows through the path of the capacitor 23 → the resistor 20 → the base of the transistor 21 → the emitter of the transistor 21, and the transistor 21 is turned on during that time, so that the MOV 13 can be connected for a long time. As described above, since the MOV 13 operates only when a surge voltage is applied and does not normally operate, the leakage current standard, the limiting voltage standard, etc. of the MOV 13 are not strictly required, or the voltage is not always applied to the MOV 13. Therefore, the present embodiment has a great effect that the MOV does not deteriorate and there is no fear of ignition, and the MOV having a low suppression voltage can be used.

The transistor 21 is an NPN in FIG.
It is filled in with a transistor, but with some changes PNP
Transistors can also be used, and Darlington transistors can also be used.

FIG. 5 shows an example of a surge absorbing circuit according to a second embodiment of the invention of claim 2 in which transistors 21 and 22 are connected in cascade to form a two-stage amplifier circuit.

FIG. 6 is a circuit diagram showing an embodiment of the invention described in claim 3, and FIG. 7 is a characteristic diagram of the bidirectional thyristor 12 in the embodiment of FIG. The operation of bidirectional thyristor 12 is as described in relation to the prior art.

In FIG. 6, 11 is an AC power source, and 2
Reference numerals 8 and 29 are ZDs, which are connected in series in opposite directions.
A bidirectional thyristor 12 is connected in series to the MOV 13 and a load 14 is provided. ZD28,
The operating voltage of 29 is set to be slightly higher than the operating voltage of MOV13. If a surge voltage is applied here, the bidirectional thyristor 12 is turned on, but the operating voltage of the ZDs 28 and 29 is set to be slightly higher than the operating voltage of the MOV 13, so the applied surge voltage is the suppression voltage of the MOV 13. It is suppressed by the value. However, when the waveform has a sharp rising edge (ns or less), the rising portion cannot be sufficiently suppressed only by the MOV 13 having a poor response characteristic, so that it is suppressed by the ZDs 28 and 29 having a good response characteristic. That is, ZD
If a circuit in which 28 and 29 are connected in series in the opposite direction and a circuit in which the bidirectional thyristor 12 and the MOV 13 are connected in series are connected in parallel, a waveform with a sharp rising edge becomes ZD2.
The surge voltage can be suppressed by the MOVs 13 and 8 and the flat waveform by the MOV 13, respectively. In the circuit in which the bidirectional thyristor 12 and the MOV 13 are connected in series, the bidirectional thyristor 12 is turned off when the current flowing in the bidirectional thyristor 12 becomes equal to or less than the holding current, and the MOV1
3 does not operate at all, and only the leak current of the bidirectional thyristor 12 flows. That is, the MOV 13 operates only when the surge voltage is applied, and does not operate in other periods.

FIG. 8 is a circuit diagram showing an embodiment of the invention described in claim 4. In FIG. In this embodiment, a Zener diode 29 is connected in parallel to a circuit in which the bidirectional thyristor 12 and the MOV 13 are connected in series. The operation of this embodiment is the same as that of the embodiment of FIG. 6, but since there is only one Zener diode, this embodiment can be applied only to the DC power supply circuit, not to the AC power supply circuit.

FIG. 9 is a circuit diagram showing an embodiment of the invention described in claim 5. The surge absorbing circuit of this embodiment is connected in parallel to a load 14 connected to an AC power supply 11, and includes a bidirectional thyristor 12 and two discharge circuits 3 and 4 connected in series to the bidirectional thyristor 12. It is configured.

The two discharge circuits 3 and 4 are connected in parallel with each other. In the discharge circuit 3, the capacitor C1 and the resistor R
1 is connected in parallel, and the diode D1 is connected in series to this. In the discharge circuit 4, the capacitor C2 and the resistor R
2 and 2 are connected in parallel, and a diode D2 is connected in series to the diode D1 in the opposite polarity to the diode D1.

Next, the operation of this embodiment will be described.

First, when a positive surge voltage is applied, the bidirectional thyristor 12 is turned on, the surge current passes through the diode D1 of the discharge circuit 3, and the surge energy is supplied to the circuit network composed of the capacitor C1 and the resistor R1. Absorb. Here, the value of the capacitor C1 is the width of the surge voltage,
It may be set according to the amplitude or the like. The resistor R1 is a discharge resistor for discharging the charge of the capacitor C1,
The value is determined by the surge interval, the time constant with the capacitor C1, and the like.

When the surge voltage is in the opposite direction, the bidirectional thyristor 12 is turned on, the surge current passes through the diode D2 of the discharge circuit 4, and the energy of the surge is absorbed by the network composed of the capacitor C2 and the resistor R2.

If the breakover voltage Vb is set so that the two-way thyristor 12 is turned on only when a surge voltage is applied, the circuit of FIG. 9 is naturally applied with the surge voltage. It only works when you turn it off, and it doesn't work normally.

As described above, it can be said that the surge absorbing circuit shown in FIG. 9 is very suitable for absorbing the surge voltage superimposed on the AC power supply circuit.

[0034]

In the surge absorbing circuit of the present invention described in claims 1 to 5, a current flows only when a surge voltage is applied. Therefore, in the invention of claims 1 to 4 using MOV, the leakage current standard and the limiting current standard of MOV are remarkably relaxed as compared with the conventional surge absorbing circuit, and the manufacturing yield of MOV is improved, and the manufacturing of MOV is improved. The price can be reduced. In addition, since no voltage is applied to the MOV at all times, there is no deterioration of the MOV over time, ignition due to self-heating can be prevented, and a MOV with a low suppression voltage value can be used.

According to the invention described in claims 3 and 4, since the Zener diode is provided, the surge voltage at the steep rising portion can be efficiently absorbed.

According to the fifth aspect of the present invention, by selecting the values of the capacitor and the resistor according to the expected time width and amplitude of the surge voltage, a circuit having an optimum time constant is constructed and the surge voltage is most appropriately set. It is possible to provide a small, lightweight, and inexpensive surge absorption circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the invention described in claim 1.

FIG. 2 is a diagram showing the terminals, current and applied voltage of a triac 10 in the circuit of FIG.

FIG. 3 is a diagram showing a second embodiment of the invention described in claim 1.

FIG. 4 is a diagram showing a first embodiment of the invention described in claim 2;

FIG. 5 is a diagram showing a second embodiment of the invention described in claim 2;

FIG. 6 is a diagram showing an embodiment of the invention described in claim 3;

7 is a characteristic diagram of the bidirectional thyristor 12 in FIG.

FIG. 8 is a diagram showing an embodiment of the invention described in claim 4;

FIG. 9 is a diagram showing an embodiment of the invention described in claim 5;

FIG. 10 is a diagram showing a conventional surge absorbing circuit made of a metal oxide varistor.

FIG. 11 is a diagram showing a conventional surge absorption circuit in which a metal oxide varistor and a bidirectional thyristor are connected in series.

FIG. 12 is a diagram showing a conventional surge absorbing circuit including a bidirectional thyristor.

[Explanation of symbols]

3,4 Discharge circuit 10 Triac 11 AC power supply 12 Two-way thyristor 13 Metal oxide varistor (MOV) 14 Load 15 DC power supply 16, 17, 25, 26, 28, 29 Zener diode 18, 19, 20, 27 Resistance 21,22 Transistor 23, 24 Capacitor 27 Diac

Claims (5)

[Claims] 1. A surge absorbing circuit comprising a triac having a gate terminal connected to a gate terminal for controlling a gate current by a surge voltage and a metal oxide varistor connected in series. 2. A surge absorption circuit for a DC circuit, comprising a Zener diode, a resistor and a base of a transistor connected in series, and a collector of the transistor connected in series with a metal oxide varistor. 3. A first circuit in which two Zener diodes are connected in series in opposite directions to each other and a second circuit in which a bidirectional thyristor and a metal oxide varistor are connected in series are connected in parallel. Characteristic surge absorption circuit. 4. A surge absorption circuit for a DC circuit, comprising a zener diode connected in parallel to a circuit formed by connecting a bidirectional thyristor and a metal oxide varistor in series. 5. A first discharge circuit in which a first diode is connected in series to a parallel connection circuit of a first capacitor and a first resistor, and a parallel connection circuit of a second capacitor and a second resistor. A second discharge circuit in which a second diode is connected in series to the first diode in reverse polarity and a two-way thyristor, and the first and second discharge circuits are connected in parallel. A surge absorbing circuit in which the bidirectional thyristor is connected in series at a connection point of both discharge circuits.