GB2161659A

GB2161659A - Apparatus for protecting against overvoltages having a coarse protection and a fine protection means

Info

Publication number: GB2161659A
Application number: GB08511293A
Authority: GB
Inventors: Wolf-Dieter Oels
Original assignee: OELS WOLF DIETER
Current assignee: OELS WOLF DIETER
Priority date: 1984-07-10
Filing date: 1985-05-03
Publication date: 1986-01-15
Also published as: DE3425296C2; GB2161659B; GB8511293D0; DE3425296A1

Abstract

The apparatus has a coarse protection means 7 and a fine protection means 8 which are spaced apart and connected together by way of a cable 3. This results in a reduction in the protection factor (ratio of maximum output voltage to nominal limiting voltage of the fire protection means). The protection means 7, 8 may be housed in respective connectors 4, 2 at the ends of the cable 3. The cable 3 may be 1 to 3 meters long and have a screen 5 connected to conductive parts of the housings of connectors 2, 4. <IMAGE>

Description

SPECIFICATION Apparatus for protecting against overvoltages having a course protection and a fine protection means The invention relates to an apparatus for protecting against overvoltages, in particular of equipment and apparatuses which are provided with electronic components, having a coarse protection and a fine protection means.

Protective circuits with coarse protection means which is provided for example with varistors and a fine protection means which is provided for example with Z-diodes and which is intended to afford protection against overvoltages are known. In that connection, the coarse protection means is intended to control high transient energies which are above the limit for destruction of the fine protection components, while the essence of the fine protection means lies in the high response speed and the low limiting voltage. The response speed of the fine protection means is substantially higher than that of the coarse protection means. The limiting voltage of the fine protection means is art a few volts, while that of the coarse protection means is some 100 volts.

Now, the essence of such protective circuits lies in particular in the fact that the two kinds of protection are to be matched to each other in such a way as to ensure a certain distribution in terms of operation between coarse protection and fine protection. In particular, the coarse protection means must respond before the fine protection means is overloaded. It is necessary to ensure that, when the circuit is loaded with quick transients, with rise times of a few nanoseconds to microseconds, an effective level of protection is afforded.

The measurement used in respect of protection factors which are to be afforded by protective circuits of that kind is generally the ratio of maximum output voltage in regard to rapid transients, in relation to the nominal limiting voltage of the fine protection components (clamping factor).

That protection factor, in conventional protective circuits, is between 1.5 and 2, the crucial consideration in regard to those high factors being the relatively high inductances of the fine protection components and their feed lines and the high current changes which occur in the direct vicinity, with frequency components in the gigahertz range, which provide for corresponding voltage excesses.

The problem of the invention is to provide a solution which makes it possible to achieve an enduring reduction in the protective factor.

According to the invention, the problem is solved in that the coarse protection means and the fine protection means are arranged separately in terms of space and connected together by way of a cable.

Surprisingly it has been found that, with a 16 V protective circuit, the protective level measured was only 20 V, which corresponds to a protection factor of 1.25. In conventional protective circuits, upon firing of an arrester, within from 1 to 4 nanoseconds, there is a firing jump from 1 kV, to 20 V. In the case of the protective circuit of conventional printed circuit board type and with a Z-diode voltage of for example 16 V, there is accordingly a maximum protective level limit of 32 V.

The invention avoids those unsatisfactory conditions.

In an embodiment, the invention provides that the coarse protection means and the fine protection means are each disposed in a plug and coupling housing respectively, which are connected together by way of the cable. The fact that the protection means are provided directly in plug and coupling housings quite considerably simplifies handling.

It has been found that it is particularly advantageous for the length of the connecting cable to be approximately in the range of from 1 to 3 metres inclusive.

A further feature of the invention provides that at least portions of the plug and coupling housings are formed from an electrically conductive material which serves for screening purposes, wherein said housing portions are electrically conductively connected together by way of the cable.

In accordance with the last-mentioned embodiment, it may also be provided that the housings are made entirely of electrically - conductive material and the cable is formed as a screened cable so that then the entire apparatus is screened.

The cable itself acts as an attenuating member in respect of high frequencies in the GHz-range so that in the fine protection means, the large changes in current which, in the state of the art, result in the high protection factors, no longer occur at all, thereby making it possible to achieve an improved protective effect.

It is also provided in accordance with the invention, as is known per se, that gas discharge arresters and/or spark gaps and/or varistors may be provided for the purposes of coarse protection, as voltage-limiting elements, and Z-diodes and/or suppressor diodes and/or transzorbs may be provided for the purposes of fine protection as voltage-limiting elements.

An embodiment of the invention will now be described in greater detail hereinafter by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of apparatus for protection against overvoltages; and Figure 2 is an explanatory circuit diagram.

As illustrated therein, a plug housing 2 is connected to a coupling housing 4 by way of a cable 3. Both the plug housing 2 and the coupling housing 4 are made from an electrically conductive material, while the housings are electrically conductively connected together, for example by way of the screening of a cable 3.

Disposed in the interior of each of the housings 2 and 4 are coarse protection means and fine protection means respectively.

A possible form of such a circuit is shown in Figure 2, for example, as an overvoltage protection cable for a V 24-interface.

The protection means shown on the left-hand side represents the cable input, that is to say, as shown in Figure 1,the cable coupling. Reference numeral 5 denotes the connection of the cable screening while reference numeral 6 denotes the connection to the housing.

The fine protection means is disposed at 2 and forms the end of the cable which is towards the device, for example the plug 2.

It should be noted at this point that, depending on the equipment and layout of the device, the fine protection means may be formed as the coupling and conversely the coarse protection means may be formed as the plug, without the invention being restricted thereto.

It will be appreciated that the above-described embodiment of the invention may also be varied in many ways without thereby departing from the basic concept of the invention. Thus in particular the invention is not restricted to the electronic components shown in the circuit diagram, for example the gas discharge arresters 7 in the coarse protection means and the Z-diodes in the fine protection means 8. Any other components which may be considered may also be provided here, without departing from the basic concept of the invention.

Claims

1. Apparatus for protection against overvoltages, having a coarse projection and a fine projection means, the coarse protection means and the fine protection means being arranged separately in terms of space and connected together by way of a cable.

2. Apparatus according to Claim 1, in which the coarse protection means and fine protection means are respectively disposed in a plug and coupling housing, which are connected together by way of a cable.

3. Apparatus according to Ciaim 1 or Claim 2, in which the length of the connecting cable is in the range between 1 and 3 inclusive.

4. Apparatus according to any one of the preceding claims, in which at least portions of the plug and coupling housings are formed from an electrically conductive material which serves for screening purposes, and said housimg portions are electrically conductively connected together by way of the cable.

5. Apparatus according to any one of the preceding claims, in which gas discharge arresters and/or spark paths and/or varistors are provided for coarse protection as voltage-limiting elements.

6. Apparatus according to any one of the preceding claims, in which Z-diodes and/or diodes andlor transzorbs are provided for fine protection as voltage-limiting elements.

7. Apparatus substantially as hereinafter described with reference to the accompanying drawings.