JPH05161258A - Surge voltage absorbing circuit - Google Patents

Abstract

PURPOSE:To provide an AC supply filter which absorbs a counter-electromotive force generated by an inductor of the AC power supply when a surge voltage is inputted due to an indirect lightning stroke and which prevents the destruction of insulating components such as a transformer and a photocoupler. CONSTITUTION:An AC supply filter is constituted of a choke coil for common mode L1 and capacitors for common mode C1-C4. Between common terminals c and d of the choke coil L1, a pulse-resistant resistor R1 is connected for absorbing a counter-electromotive force generated by an inductor when a surge voltage is inputted. When two choke coils are subordinately connected, the pulse-resistant resistor is connected to the one with larger inductance.

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 preventing damage to the device from surge voltage caused by inductive lightning that enters an AC power line.

[0002]

BACKGROUND OF THE INVENTION There are two types of lightning surge tests, normal mode and common mode.
C801, CISPR / G / WG (S) 10, IEEE
It has been established that the application of standards such as -607 will be adopted from 1996. These standards are set for the purpose of preventing insulation breakdown of equipment from high-energy induced lightning and switching surges. The standard of IEC801, which is an example of the standard of this lightning surge test, is shown in FIG.
Looking at the standard of EC801, especially when the surge input is the common mode, when the severity level is 4, the open circuit voltage is 4.
A test level such as 0 kV and a short circuit current of 1.0 kA is required, and a surge voltage absorption circuit that can prevent the breakdown of the device due to the surge voltage is required.

[0003]

2. Description of the Related Art Several conventional surge voltage absorption circuits have been proposed. One of them is to create an air gap on a printed circuit board between line grounds for discharging.
Although measures were taken by inserting a discharge element, in the case of an air gap, there are large variations due to the effects of temperature and humidity, and since the discharge element is inserted between the line grounds, it is essential to obtain a safety standard product. However, such a discharge element still does not exist and it is difficult to commercialize it in the future.

As another example, inductive noise such as lightning may come in from a commercial power supply line through a DC power supply. Although these noises are propagated in the common mode and the normal mode, an AC line power supply filter is used to prevent the intrusion of this external noise. Figure 3
As shown in FIG. 3, the AC power supply filter is connected between the normal lines A-B and the common line safety grounds A-E and B-.
Common mode capacitors C1, C2 connected between E,
It is composed of C3, C4 and an inductor L1 forming a common mode choke coil, and is connected so as to be located between the AC line and the switching power supply or the power supply transformer 1.
A problem that occurs when a surge voltage equivalent to the induced voltage due to lightning or the like is input to the AC line when such an AC power filter is connected will be described. In addition, D1
Is a full-wave rectifier circuit.

The surge voltage is applied to the line A and the safety ground E.
If a common mode voltage is applied between line B or line B and safety earth E, there is a problem that components such as transformers and photocouplers on the switch power supply 1 side will be damaged due to insulation failure, and the cause is unknown until now. It was This is because a back electromotive force is generated in the inductor L1 and a voltage about twice the applied voltage is applied between the primary and secondary parts of the transformer and the photocoupler which insulate the primary and secondary parts. It became clear.

[0006]

SUMMARY OF THE INVENTION The present invention is an AC power supply capable of absorbing a counter electromotive force generated by the induction of an AC power supply filter due to the input of a surge voltage and preventing the destruction of insulating parts such as a transformer and a photocoupler. The point is to provide a filter.

[0007]

The present invention is characterized in that a pulse resistance resistor is connected in parallel between common input / output terminals of an inductor constituting an AC power supply filter.

[0008]

1 shows a circuit of a first embodiment of an AC power supply filter of the present invention. In this AC power supply filter circuit, a pulse resistance R1 is connected in parallel between the common terminals cd of the inductor L1. This pulse resistance R1 is 2
W, about 1 to several KΩ is sufficient. Even if a surge voltage is input to the AC power supply filter to which the pulse resistance R1 is connected, the high voltage due to the back electromotive force generated in the inductor L1 is applied to both ends of the pulse resistance R1 and is absorbed as a power loss. Therefore, the back electromotive force can be prevented from being destroyed in these insulating parts without being applied to the transformer or the photocoupler. The capacitors C1 to C4 have the same function as the conventional example.

FIG. 2 shows a second embodiment of the present invention, in which A
The C power supply filter is cascade-connected in two stages. In the case of this embodiment, inductors L2 and L3 (L2
> L3), when the pulse resistance R2 is connected in parallel between the common terminals cd of the inductor L2 having a large inductance and a large back electromotive force generated, the absorption of the back electromotive force due to the surge voltage is effective. The capacitors C5 to C7 are common mode capacitors as in the above embodiment.

Although not shown, in the second embodiment, the pulse resistance may be connected in parallel to the inductor L3, or the pulse resistance may be connected between the common terminals of the inductors L2 and L3. It is possible. Further, in order to reduce the high frequency impedance and enhance the absorption effect, the pulse resistance R2 and the capacitor C8 may be connected in series.

[0011]

According to the present invention, it is possible to realize an AC power supply filter which has a simple structure and is capable of absorbing counter electromotive force due to a surge voltage, which is simple in structure with respect to lightning surge standards such as IEC801.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of a surge voltage absorption circuit of the present invention.

FIG. 2 is a circuit diagram of a second embodiment of the surge voltage absorption circuit of the present invention.

FIG. 3 is a circuit diagram of a conventional AC power supply filter.

FIG. 4 is a table showing an international standard of lightning surge protection.

[Explanation of symbols]

1 .. Switching power supply C1 to C4 .. Capacitor
LI ... Inductor R1, R2 ... Pulse resistance

Claims (2)

[Claims] 1. A composed of an inductor and a capacitor
A surge voltage absorbing circuit characterized in that a pulse resistance is inserted in the inductor of the C power supply filter. 2. The surge voltage absorption circuit according to claim 1, wherein a capacitor is connected in series with the pulse resistance resistor.