JPH09172733A - Surge voltage absorbing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the damage of a semiconductor caused by the counterelectromotive voltage generated at an inductor when there is an entry of surge voltage by thunderbolt, etc., or a sudden change of input voltage. SOLUTION: In case that the surge voltage in common code enters between a line L and a frame ground FG, the surge energy is absorbed by the course from a discharge electrode Al to a metallic oxide varistor B1 being a second constant voltage element or a course from the inductor L1 in common code to a line path bypass capacitor C4. In case the surge voltage in common code enters between the neutral N and frame ground FG, the surge voltage is absorbed by the course from a discharge electrode A2 to a metallic oxide varistor B1 or the course from the inductor L1 to a line path bypass capacitor C3. The counterelectromotive power generated in the inductor L1 in common mode is clamped by a constant voltage element excellent in surge responsiveness, and also the surge voltage above it is absorbed in the constant voltage element 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge voltage absorption circuit for absorbing internal and external surge voltages in an AC input section of electronic equipment such as OA equipment, and more particularly to a surge voltage absorption circuit suitable for a switching regulator.

[0002]

2. Description of the Related Art A switching regulator can be made compact, lightweight and highly efficient because a converter transformer is driven at a high frequency (50 KHz to 200 KHz) and control is intermittent so that loss is small. Therefore, it is mostly used as a power source for electronic devices such as recent office automation equipment. However, such a switching regulator has the following drawbacks.

For example, due to the intrusion of an induced surge voltage due to a lightning strike, the intrusion of a surge voltage due to the turning on and off of a high power electronic device such as a machine tool, an air conditioner, etc., an alternating current input from a commercial power supply includes a harmonic current. Has been.
When these surge voltages intrude between the AC input line L-neutral N, between the line L-frame ground FG, and between the neutral N-frame ground FG, the surge voltage may reach 10 KV in some cases, which causes switching. There is a risk that semiconductor elements such as transistors will be destroyed.

Also, the switching regulator itself generates a lot of noise. Therefore, although a noise is reduced by providing a snapper circuit in the vicinity of the switching element of the noise generator, the noise flowing from the AC input unit to the outside of the power supply is reduced. In order to suppress it, it is also necessary to reduce noise in the AC input section.

As a conventional surge voltage absorbing circuit, for example, there is one disclosed in Japanese Patent Laid-Open No. 5-161258. FIG. 19 shows the configuration thereof, in which the AC power supply filter is configured by the common mode choke coil L1 and the common mode capacitors C1 to C4, and the pulse resistance R1 is connected between the common terminals cd of the choke coil L1. The counter electromotive force generated by the inductor L1 due to the input of the surge voltage is absorbed. Further, a method of connecting a pulse resistance R1 and a series body of a capacitor between the common terminals cd has been proposed.

The above conventional noise filter not only suppresses conduction noise (noise terminal voltage), radiation noise (electric field, magnetic field) and surge voltage flowing out of the switching power supply, but also external noise and surge voltage. The electronic device can be protected against the intrusion of.

[0007]

However, in the above-mentioned conventional surge voltage absorption circuit, the normal mode surge voltage energy that has entered between the AC input line and the neutral is absorbed by each element of the noise filter, and in particular, the inductor L1 is generated. Since the counter electromotive force of high voltage is absorbed by the pulse resistance R1 as a power loss, there is a problem that a current constantly flows into the pulse resistance R1 and a power loss due to the pulse resistance R1 and accompanying heat generation occur. is there. In addition, when a surge voltage exceeding the rated power of the pulse resistance R1 is applied, there is a risk of fire or the like due to damage of the pulse resistance R1 or fusing of the pattern, and the accompanying heat generation and smoke generation. It becomes a big problem in safety and reliability of electronic equipment such as equipment.

In view of the above problems of the prior art, the present invention provides a safe and reliable method for preventing damage to a semiconductor due to a back electromotive force generated in an inductor when a surge voltage enters due to a lightning strike or when an input voltage changes suddenly. An object is to provide a high surge voltage absorption circuit.

[0009]

In order to achieve the above-mentioned object, a first means is a common mode first constant voltage element in which two discharge electrodes are connected in series between AC input lines, and the discharge. A common mode second constant voltage element connected between the connection point of the electrode and the frame ground, a common mode inductor and a normal mode line capacitor connected between the AC input lines, and the common mode inductor And a third constant voltage element connected in parallel to both ends of the.

The second means is such that, in the first means, a fourth constant voltage element is further connected between the AC input lines in the latter stage of the first constant voltage element and in the former stage of the inductor and the line capacitor. It is characterized by being

A third means is characterized in that a fifth constant voltage element is further connected to the latter stage of the inductor and the line capacitor in the first or second means.

A fourth means is a common mode first connection in which two discharge electrodes are connected in series between AC input lines.
Constant voltage element, a common mode second constant voltage element connected between the connection point of the discharge electrode and the frame ground, a common mode inductor connected between AC input lines, and a normal mode line A capacitor,
A normal mode inductor connected between the AC input lines and a third constant voltage element connected in parallel to both ends of the normal mode inductor are provided.

A fifth means is characterized in that, in the fourth means, a fourth constant voltage element is further connected between the AC input lines in the preceding stage of the normal mode inductor.

A sixth means is the fifth or fifth means, further including a fifth stage after the normal mode inductor.
Is connected to the constant voltage element.

In a seventh means, in the first to sixth means, one or more of a gas tube arrester, a metal oxide varistor and a resistor are connected in series in the third, fourth and fifth constant voltage elements. It is characterized in that it is a circuit.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a switching regulator provided with an embodiment of a surge voltage absorption circuit according to the present invention.

In FIG. 1, this switching regulator is roughly composed of an input section 1, a noise filter section 2, a rectifying / smoothing section 3 and a switching power supply section 4, and the noise filter section 2 constitutes a surge voltage absorbing circuit. ing. In the input section 1, one end of a fuse F1 for overcurrent protection is connected to the line L of the commercial power source. In the noise filter unit 2, between the line L (the other end of the fuse F1) and the neutral N, in order to reduce the common mode noise generated in the AC line, from the discharge electrodes A1 and A2 configured by connecting two elements in series. The first constant voltage element is connected, and a metal oxide varistor B1 is connected as a second constant voltage element between the connection point of the constant voltage elements A1 and A2 and the frame ground FG.

In the noise filter section 2, the line L-
Across the line capacitors C1 and C2 are connected between the neutral N to reduce the normal mode noise generated in the AC line, and further, a common mode inductor (choke coil) L1 is connected, and A line bypass capacitor C3 is connected between the neutral N-frame ground FG, and a line bypass capacitor C4 is connected between the line L-frame ground FG. Further, the constant voltage element 5 is connected in parallel with the inductor L1.

The rectifying / smoothing unit 3 rectifies and smoothes the alternating current that has passed through the noise filter unit 2 by the full-wave rectifying circuit D1 and the smoothing capacitor C5, respectively, and the switching power supply unit 4 uses the rectifying / smoothing unit 3 as well known. The full-wave rectified and smoothed primary DC power is turned on / off by a switching element connected in series to the primary winding of a transformer (not shown), and the power induced in the secondary winding of the transformer is further rectified. , And outputs the secondary DC power obtained by smoothing. The switching power supply unit 4 also controls the duty ratio of the switching element in order to stabilize the secondary DC power.

In such a structure, when a common mode surge voltage enters between the line L and the frame ground FG, the line L → the discharge electrode A1 which is the first constant voltage element of the noise filter section 2 → The path of the second constant voltage element, metal oxide varistor B1 → frame ground FG, or line L → common mode inductor L1 → line
The surge energy is absorbed along the path from the bypass capacitor C4 to the frame ground FG.

When a common mode surge voltage enters between the neutral N and the frame ground FG, it is as follows: neutral N → discharge electrode A2 which is the first constant voltage element of the noise filter section 2 → second constant voltage Metal oxide varistor B1 which is a voltage element → route of frame ground FG,
Or line L → common mode inductor L1 → line
The surge energy is absorbed through the path from the bypass capacitor C3 to the frame ground FG.

As a result, the common mode inductor L1
Back electromotive force is generated in the line L-neutral N
A counter electromotive force is generated in the inductor L1 even when a normal mode surge voltage intrudes in the meantime. Then, this counter electromotive force is clamped by the constant voltage element 5 having excellent surge response, and a surge voltage higher than that is absorbed inside the constant voltage element 5.

Next, a second example will be described with reference to FIG. In this second example, the constant voltage element 6 is added to the first example shown in FIG. 1, and the other configurations are the same as those in the first example. The constant voltage element 6 is inserted between the line L and the neutral N in the latter stage of the first constant voltage elements A1 and A2 and in the former stage of the filter unit 2 (capacitor C1).

In such a structure, when a normal mode surge voltage intrudes between the line L and the neutral N, most of it is absorbed by the constant voltage element 6, but lightning surge and the like are in the normal mode and the common mode. Since the respective components are mixed, the constant voltage element 6 alone cannot absorb the components and a counter electromotive force is generated in the inductor L1. In this case, this back electromotive force is clamped by the constant voltage elements 5 and 6, and a surge voltage higher than that is absorbed inside the constant voltage element 5.

When the surge energy that has entered is extremely large and exceeds the surge withstand voltage of the constant voltage element 6, the constant voltage element 6 is broken in the short mode, and the fuse F1 of the input section 1 is broken. There is also a case where the electronic device goes down and the system goes down. According to the Central Research Institute of Electric Power Industry, the discharge current due to the lightning rod is almost 200 A
It is reported below that about 200% exceeds 5%. Considering this, in order to prevent the system down of the electronic equipment, it is sufficient to select the constant voltage element 6 having a surge current withstand capability of 1000A to 1250A with a safety factor of 5 to 6 times the discharge current of 200A. Become.
Further, when high reliability is required, the constant voltage element 6
As the above, one having a larger surge current withstanding capability may be selected.

In the third example shown in FIG. 3, the constant voltage element 7 is inserted between the line L and the neutral N in the subsequent stage of the filter section 2 (capacitor C2) in the first example. Similarly, in this example, when the normal mode surge voltage intrudes between the line L and the neutral N and the counter electromotive force is generated in the inductor L1, the counter electromotive force is generated by the constant voltage elements 5 and 7.
Is clamped by and the surge voltage beyond that is absorbed inside the constant voltage element 5.

The fourth example shown in FIG. 4 is a combination of the second example shown in FIG. 2 and the third example shown in FIG. 3, in which the constant voltage element 6 is the first constant voltage element A1, The line L- in the latter stage of A2 and in the former stage of the filter unit 2 (capacitor C1)
The constant voltage element 7 is inserted between the neutral N and the line L-neutral N in the subsequent stage of the filter unit 2 (capacitor C2). Similarly in this example,
When a normal mode surge voltage intrudes between the line L and the neutral N and a counter electromotive force is generated in the inductor L1, this counter electromotive force is clamped by the constant voltage elements 5, 6 and 7, and further surges occur. Voltage is constant voltage element 5
Absorbed inside.

FIG. 5 shows a specific example of the constant voltage elements 5-7.
The case where gas tube arresters A3, A4, A5 are used is shown. Due to the characteristics of the gas tube arresters A3 to A5, almost no current flows up to the discharge start voltage, but gas discharge starts when the inter-terminal voltage exceeds the discharge start voltage, and discharge occurs when the inter-terminal voltage becomes lower than the discharge start voltage. A constant discharge voltage is maintained regardless of the magnitude of the current. Further, when the voltage between the terminals becomes lower than the discharge starting voltage, the discharge is stopped and the state before the discharge is started is restored. If the surge voltage is very high or the discharge current is too large, arc discharge will occur instead of gas discharge, resulting in a short circuit between both terminals, and discharge will not stop even if the voltage becomes lower than the discharge voltage. The discharge electrode may melt and be damaged.

FIG. 6 shows another example of the constant voltage elements 5 to 7 which is a zinc oxide varistor B2, B which is a metal oxide varistor.
3 shows the case where B4 is used. The zinc oxide varistor B2 to B4 has a characteristic that the voltage across its terminals is approximately proportional to the logarithm of the current, like other metal oxide varistor or silicon carbide varistor. Conversely, since the current changes substantially in proportion to the exponential function of the voltage between terminals, when the voltage between terminals exceeds a certain value, the current flowing through the varistor increases rapidly, and this characteristic causes the zinc oxide varistors B2 to B4. Constant voltage element 5-7
Can be used as

Unlike the gas tube arresters A3 to A5, the zinc oxide varistors B2 to B4 allow a slight current (leakage current) to flow even at a low voltage, and a leak current that cannot be ignored at a certain value flows. Should be much higher than the peak voltage of the AC power supply.
Also, from the viewpoint of absorbing surge voltage, there is an advantage that it is much smaller than the gas tube arresters A3 to A5, but when surge voltage and power are large, the terminals are shorted due to heat generation due to the power loss. Sometimes it becomes.

FIG. 7 shows another specific example of the constant voltage elements 5 to 7 in which gas tube arresters A3 to A5 and metal oxide varistors (in this example, zinc oxide varistors B2 to B4) are connected in series. There is. In this case, by lowering the varistor voltage of the zinc oxide varistor B2 to B4 below the discharge starting voltage of the gas tube arresters A3 to A5, the zinc oxide varistor B2 to B4 prevents a follow-up current and quickly absorbs the surge voltage. can do.

When a surge voltage is applied to this series circuit, current does not always flow through the gas tube arresters A3 to A5 as described above, so that the surge voltage at the time of rising is almost between the terminals of the gas tube arresters A3 to A5. Applied to. When the surge voltage exceeds the discharge voltage, the gas tube arresters A3 to A5 start to discharge, and the voltage between the terminals of the zinc oxide varistors B2 to B4 drops by the discharge voltage of the gas tube arresters A3 to A5. Is applied and a current starts to flow, and when the voltage between the terminals drops below the discharge voltage, the gas tube arresters A3 to A5 stop the discharge and return to the state before the start of discharge.

FIG. 8 shows gas tube arresters A3 to A5 and resistors R1 to R3 as another specific example of the constant voltage elements 5 to 7.
Are connected in series. The gas tube arresters A3 to A5 are used for discharging, and resistors R1 to R3 are used to prevent a follow-up current and to quickly absorb the surge voltage.

When a surge voltage is applied to the surge voltage absorbing circuit of the series circuit, as described above, current does not always flow through the gas tube arresters A3 to A5, so that the surge voltage at the time of start-up is almost the same as the gas tube arrester A3.
To A5 terminals. When the surge voltage exceeds the discharge voltage, gas tube arresters A3 to A5
Starts to discharge, and a voltage dropped from the surge voltage by the discharge voltage of the gas tube arresters A3 to A5 is applied between the terminals of the resistors R1 to R3 and consumed as power loss.
When the voltage between the terminals of the gas tube arresters A3 to A5 becomes lower than the discharge voltage, the discharge is stopped and the state before the start of discharge is restored.

In FIG. 9, a metal oxide varistor B2 is used as the constant voltage element 5, and a gas tube arrester A is used as the constant voltage element 6.
4 and a gas tube arrester A as a constant voltage element 7.
5 shows a case where the resistor 5 and the resistor R4 are connected in series. Further, a gas tube arrester, a metal oxide varistor, and a resistor may be appropriately combined as the constant voltage elements 5 to 7.

In the above example, the case where the inductor L1 is arranged between the fuse F1 and the noise filter section 2 has been described, but it may be arranged between the noise filter section 2 and the rectifier circuit D1 or smoothed with the rectifier circuit D1. The same effect can be obtained for the configuration arranged between the capacitors C5. In addition, the constant voltage element 5 connected in parallel to the inductor L1
In the above description, the case of arranging on the neutral N side has been described, but the same effect can be obtained for the structure arranged on the line L side, and if it is arranged on both the neutral N side and the line L side, a higher effect can be obtained. Is obtained. Further, a resistor may be used as the second constant voltage element instead of the metal oxide varistor B1.

Next, a fifth example will be described with reference to FIG. The input unit 1, the rectifying / smoothing unit 3, and the switching power supply unit 4 shown in FIG. 10 are the same as those in the first to fourth examples, and the noise filter unit 2a is different. In the noise filter unit 2a, one end of a normal mode inductor L2 is connected to the line L (the other end of the fuse F1) to reduce the harmonic current, and the constant voltage element 5 is connected to both ends of the inductor L2.
Are connected in parallel.

The latter stage of the inductor L2 and the constant voltage element 5 is substantially the same as the first to fourth examples, and two lines are provided between the line L and the neutral N to reduce common mode noise generated in the AC line. A first constant voltage element composed of discharge electrodes A1 and A2 configured by series connection of elements is connected, and a second constant voltage element is provided between the connection point of the constant voltage elements A1 and A2 and the frame ground FG. A metal oxide varistor B1 is connected as. Further, across the line capacitors C1 and C2 are connected between the line L and the neutral N to reduce normal mode noise generated in the AC line, and further, a common mode inductor L1 is connected. , A line bypass capacitor C3 is connected between the neutral N-frame ground FG, and a line bypass capacitor C4 is connected between the line L-frame ground FG.

In such a configuration, when a common mode surge voltage enters between the line L and the frame ground FG: line L → normal mode inductor L2 → first constant voltage element of the noise filter section 2 Discharge electrode A1 →
The second constant voltage element is a metal oxide varistor B1 → frame ground FG or a line L → normal mode inductor L2 → common mode inductor L1 → line bypass capacitor C4 → frame ground FG Energy is absorbed.

In this case, the normal mode inductor L
A back electromotive force is generated in 2. Similarly, when a normal mode surge voltage enters between the line L and the neutral N, a counter electromotive force is similarly generated in the normal mode inductor L2. The generated back electromotive force is clamped by the constant voltage element 5 having excellent surge response, and
Further surge voltage is absorbed inside the constant voltage element 5.

The sixth example shown in FIG. 11 is a combination of the fifth example shown in FIG. 10 and the second example shown in FIG. That is, a constant-voltage element 6 is added to the fifth example shown in FIG. 10, and this constant-voltage element 6 is the latter stage of the input unit 1 and the line in the former stage of the inductor L2 and the constant-voltage element 5 in the normal mode. It is inserted between L-neutral N.

In such a configuration, when a normal mode surge voltage enters between the line L and the neutral N, a common mode surge voltage is generated between the line L and the frame ground FG and between the neutral N and the frame ground FG. When intruding, the inrush surge voltage and the counter electromotive force generated in the inductor L2 cause the constant voltage element 5,
The surge voltage is clamped by 6 and further surge voltage is absorbed inside the constant voltage element 5.

The seventh example shown in FIG. 12 is a combination of the fifth example shown in FIG. 10 and the third example shown in FIG.
The constant voltage element 7 is added to the fifth example shown in FIG. This constant voltage element 7 is a normal mode inductor L
2 and the first constant voltage element A, which is the latter stage of the constant voltage element 5.
1 and A2 are inserted between the line L and the neutral N in the preceding stage.

When a normal mode surge voltage enters between the line L and the neutral N, and when a common mode surge voltage enters between the line L and the frame ground FG and between the neutral N and the frame ground FG, This surge voltage and inductor L2
The counter electromotive force generated at is clamped by the constant voltage elements 5 and 7, and the surge voltage higher than that is absorbed inside the constant voltage element 5.

An eighth example shown in FIG. 13 is a constant voltage element 6,
7 is added so that the surge voltage that has entered and the counter electromotive force that has occurred in the inductor L2 are similarly clamped by the constant voltage elements 5 to 7, and surge voltages higher than that are absorbed inside the constant voltage element 5. It

FIG. 14 shows the case where gas tube arresters A3 to A5 are used as the constant voltage elements 5 to 7, and FIG. 15 shows the case where metal oxide varistors B2 to B4 are used as the constant voltage elements 5 to 7. Reference numeral 16 denotes gas tube arresters A3 to A5 and metal oxide varistor B2 as constant voltage elements 5 to 7.
To B4 are connected in series, and FIG. 17 shows gas tube arresters A3 to A as constant voltage elements 5 to 7.
5 and resistors R1 to R3 are connected in series, and FIG. 18 shows a metal oxide varistor B2 as a constant voltage element 5.
Shows the case where the gas tube arrester A4 is used as the constant voltage element 6 and the gas tube arrester A5 and the resistor R4 are connected in series as the constant voltage element 7.

In the above example, the inductor L2 is arranged between the fuse F1 and the noise filter section 2, but it is arranged between the noise filter section 2 and the rectifier circuit D1 or smoothed with the rectifier circuit D1. The same effect can be obtained for the configuration arranged between the capacitors C5.
The constant voltage element 5 connected in parallel with the inductor L2
Has been described for the case of arranging on the neutral N side, the same effect can be obtained for the structure arranged on the line L side, and further high effect can be obtained by arranging on both the neutral N side and the line L side. Is obtained. Further, a resistor may be used as the second constant voltage element instead of the metal oxide varistor B1.

[0048]

As described above, according to the first aspect of the present invention, since the third constant voltage element is connected in parallel to both ends of the common mode inductor, the surge voltage is intruded by a lightning strike or the input voltage is increased. The back electromotive force generated in the inductor when the voltage changes suddenly can be absorbed by the third constant voltage element, and therefore, the semiconductor can be prevented from being damaged,
Further, it is possible to realize a surge voltage absorption circuit with high safety and reliability.

According to the second aspect of the present invention, since the fourth constant voltage element is further connected between the AC input lines after the first constant voltage element and before the inductor and the line capacitor, a lightning strike or the like occurs. The back electromotive force generated in the inductor at the time of surge voltage intrusion or sudden change of input voltage due to
It is possible to absorb by the fourth constant voltage element, and therefore, it is possible to prevent damage to the semiconductor, and it is possible to realize a surge voltage absorbing circuit with high safety and reliability.

According to the third aspect of the invention, since the fifth constant voltage element is further connected to the latter stage of the inductor and the line capacitor, it is generated in the inductor when a surge voltage enters due to a lightning strike or when the input voltage suddenly changes. The back electromotive force is the third
To the fifth constant voltage element, so that the semiconductor can be prevented from being damaged, and
It is possible to realize a surge voltage absorption circuit with high safety and reliability.

According to the fourth aspect of the present invention, since the third constant voltage element is connected in parallel to both ends of the normal mode inductor, the third constant voltage element is generated in the inductor when a surge voltage enters due to a lightning strike or when the input voltage suddenly changes. It is possible to absorb the counter electromotive voltage generated by the third constant voltage element, and therefore prevent damage to the semiconductor, and realize a surge voltage absorption circuit with high safety and reliability.

According to the fifth aspect of the invention, a fourth circuit is further provided between the AC input lines in the preceding stage of the normal mode inductor.
Since the constant voltage element of is connected, the counter electromotive voltage generated in the inductor at the time of inrush of surge voltage due to lightning strike or sudden change of input voltage can be absorbed by the third and fourth constant voltage elements. Can be prevented, and a surge voltage absorption circuit with high safety and reliability can be realized.

According to the sixth aspect of the invention, since the fifth constant voltage element is further connected to the latter stage of the normal mode inductor, it is generated in the inductor when a surge voltage enters due to a lightning strike or when the input voltage suddenly changes. The back electromotive force can be absorbed by the third to fifth constant voltage elements, and therefore, the semiconductor can be prevented from being damaged, and a surge voltage absorbing circuit with high safety and reliability can be realized. it can.

According to the seventh aspect of the invention, the third, fourth and fifth constant voltage elements are circuits in which one or more of the gas tube arrester, the metal oxide varistor and the resistor are connected in series. These constant voltage elements can absorb the counter electromotive voltage generated in the inductor when surge voltage enters due to lightning strike or when the input voltage changes suddenly.
It is possible to prevent damage to the semiconductor, and to realize a surge voltage absorption circuit with high safety and reliability.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching regulator provided with an embodiment of a surge voltage absorption circuit according to the present invention.

FIG. 2 is a circuit diagram showing a switching regulator including a surge voltage absorption circuit according to a second example.

FIG. 3 is a circuit diagram showing a switching regulator including a surge voltage absorbing circuit according to a third example.

FIG. 4 is a circuit diagram showing a switching regulator including a surge voltage absorption circuit according to a fourth example.

5 is a circuit diagram showing a specific example of the constant voltage element of FIG.

FIG. 6 is a circuit diagram showing another specific example of the constant voltage element of FIG.

FIG. 7 is a circuit diagram showing another specific example of the constant voltage element of FIG.

8 is a circuit diagram showing another specific example of the constant voltage element of FIG.

9 is a circuit diagram showing another specific example of the constant voltage element of FIG.

FIG. 10 is a circuit diagram showing a switching regulator including a surge voltage absorption circuit of a fifth example.

FIG. 11 is a circuit diagram showing a switching regulator including a surge voltage absorption circuit of a sixth example.

FIG. 12 is a circuit diagram showing a switching regulator including a surge voltage absorption circuit of a seventh example.

FIG. 13 is a circuit diagram showing a switching regulator including a surge voltage absorption circuit according to an eighth example.

14 is a circuit diagram showing a specific example of the constant voltage element of FIG.

FIG. 15 is a circuit diagram showing another specific example of the constant voltage element of FIG.

16 is a circuit diagram showing another specific example of the constant voltage element of FIG.

FIG. 17 is a circuit diagram showing another specific example of the constant voltage element of FIG.

FIG. 18 is a circuit diagram showing another specific example of the constant voltage element of FIG.

FIG. 19 is a circuit diagram showing a conventional surge voltage absorption circuit.

[Explanation of symbols]

 A1 to A5 discharge electrodes Z1 to Z3 metal oxide varistor R1 to R3 resistances L1 and L2 inductors C1 to C4 capacitors 5 to 7 constant voltage element

Claims (7)

[Claims] 1. A common mode first constant voltage element in which two discharge electrodes are connected in series between AC input lines, and a common mode first constant voltage element connected between a connection point of the discharge electrodes and a frame ground. 2 constant voltage element, a common mode inductor and a normal mode line capacitor connected between the AC input lines, and a third constant voltage element connected in parallel to both ends of the common mode inductor. Surge voltage absorption circuit. 2. A fourth constant voltage element is further connected between the AC input lines at the latter stage of the first constant voltage element and at the former stage of the inductor and the line capacitor. Surge voltage absorption circuit described. 3. The surge voltage absorption circuit according to claim 1, further comprising a fifth constant voltage element connected downstream of the inductor and the line capacitor. 4. A common mode first constant voltage element in which two discharge electrodes are connected in series between AC input lines, and a common mode first constant voltage element connected between a connection point of the discharge electrodes and a frame ground. 2 constant voltage element, a common mode inductor and a normal mode line capacitor connected between the AC input lines, a normal mode inductor connected between the AC input lines, and both ends of the normal mode inductor. A surge voltage absorbing circuit including a third constant voltage element connected in parallel. 5. The surge voltage absorbing circuit according to claim 4, wherein a fourth constant voltage element is further connected between the AC input lines in the preceding stage of the normal mode inductor. 6. The surge voltage absorption circuit according to claim 4, further comprising a fifth constant voltage element connected to the latter stage of the normal mode inductor. 7. The third, fourth, and fifth constant voltage elements are circuits in which one or more of a gas tube arrester, a metal oxide varistor, and a resistor are connected in series. 7. The surge voltage absorption circuit according to any one of 6 to 6.