PROTECTIVE DEVICE AGAINST ELECTROSTATIC DISCHARGES ON ELECTRONIC EQUIPMENT IN GENERAL

Abstract: The device consists of a combination of circuits including a first antenna circuit to pick up the electric field created by an electrostatic discharge, which sends an enabling signal, upon systematic suppression of noises on power line by means of a second circuit, to a third generating a following start signal with a desired time sequence, so that a fourth interface circuit, enabled by this start signal and galvanically connected to the equipment to be protected, is able to send a sequence of monitoring signals to the equipment, thus preventing an irregular operation of the equipment itself. Advantages: low cost, immunity up to 10 KV easily achieved, adaptability to various equipment.

Description: "PROTECTIVE DEVICE AGAINST ELECTROSTATIC DISCHARGES ON ELECTRONIC EQUIPMENT IN GENERAL" This invention belongs to the technical field of protective and monitoring industrial equipment and it refers to a protective device against electrostatic discharges on electronic equipment in general. It is well known that in the field of electronic devices protection against electronic discharges is a factor of vital importance to be taken into account during the design phase. With the introduction of modern, circuit- integration technologies such as C-MOS, MOS and the like, it is necessary to avoid any anomalous stress of the normal operating parameters of the circuits, because in this case each electronic board formed by such circuits would interpret the anomalous stress as a particular input signal, resulting in an output causing the corresponding equipment to operate in an unforeseeable way and surely bringing about negati e consequences. To this end, var ous regulations have been passed hich provide for the protection against electrostatic discharges up to 4 KV as, for instance, for cash registers. Such a protection is represented by the capacity of the equipment - in this case the cash registers - to carry electrostatic discharges up to 4 KV without any anomalous operation. Many solutions have been taken in order to overcome these technical problems and to comply with the legal regulations in force. A first solution foresees the use of multi-layer printed boards for the various electric/electronic circuits assembled thereon. In this way, the stratigraphic structure of the above-mentioned boards represents a fairly good insulating and dispersive means for possible discharges which affect the equipment itself, at the same time they protect the circuits of the equipment from possible stresses which could be interpreted as ne input signals, which are certainly anomalous and detrimental for the equipment. Besides, this solution involves high industrial costs and an average time of productive development months/man. Anyway the practical results do not guarantee both a stable answer to the event and the universal applicability of the solution itself to any kind of equipment. A second solution is represented by the dead ground which extends on the whole board to be protected, together with a number of quality capacitors suitably arranged on the board i self. In this way the circuits of the board to be protected can be virtually insulated, thus preventing any galvanic connection with external signals . Even this solution, however, has its limitations. » Infact the development times of the board provided with the above-mentioned dead grounds are long and moreover it is necessary to mount on the board also all the required capacitors involved by such solution. As a consequence the production times become longer and the corresponding costs higher and nonetheless this cannot be considered a totally reliable solution. Finally, a third solution employes special conductive paints or covering plastic materials, ich cover the whole plate to be protected. This solution provides an insulation coating on the hole circuitry assembled and arranged on the boa rd . In this way, an external signal can unlikely enter into the circuit, here considered, without a precise galvanic connection, hindered by such protective solution. In spite of this, also such a solution which, as a rule, is the most often adopted in industry, involves some problems. First of all, the production process is more onerous and then the results are not always positive. As a matter of fact, this film coating must be applied in the last phase of the production process and for this reason the production time becomes much longer and its costs much higher. Moreover, this kind of coating can guarantee only a certain degree of protection, since above which, the results are uncertain. Finally, another aspect common to all above- mentioned solutions to be considered, is that almost always the protection problems are tackled only when the equipment has already been totally assembled. As a consequence, the extra time required to determine the best solution of the problem hinders the actual planning completion of the equipment itself, involving high and not controllable co ts, esDβcially in case of variations of the equipment hardware. The main object of this invention is to eliminate the above-mentioned drawoacks with reference to the systems currently used, realizing and providing a protective device against electrostatic discharges on electronic equipments, in general, which is able to guarantee a real feature improvement of reliability, flexibility and protection realization, which reference is made to. Further advantages and features are attained, in the following description according to the present invention, by a protective device against electrostatic discharges for electronic equipment in general, charachterized in that it consists of a combination of no n circuits including a first antenna circuit to pick up the electric field created by an electrostatic discharge, which sends an enabling signal, upon systematic suppression of noises on power line by means of a second c rc , to a third circuit generating a following start signal with a desired time sequence, so that a fourth interface circuit, enabled by this start signal and galvaπically connected to the equipment to be protected, can send a seq ence of monitoring signals to this equipment, thus preventing any irregular operation of the equipment itself. Further characteristics and advantages of the invention can be gathered from the following detailed description of a preferred, but not exclusive, embodiment of a protective device against electrostatic discharges on electronic equipment in general, reference being made to the accompanying drawing, which has a mere indicative value and thus noπ limitative, which shows a preliminary block diagram of the device according to the present invention. Referring to the figure, the number 6 indicates the device according to the present invention, as a whole. An antenna circuit 1, which is fundamentally nown, acts as a sensor of an electric field created by an electrostatic discharge . At each tracking this circuit 1 triggers a monostable circuit 2 which acts as a signal generator. Another circuit 3, which is also known, works in parallel with the circuit 1 ,- so that no spurious signals such as those caused by the noises of the power line can reach the circuit 2. Finally, trough an interface circuit 4 the device 6 can be fitted to every equipment 5 according to a sequence of a plurality of signals 4a, 4b at least one of which disconnects the equipment. This structural description of the device is now followed by a detailed analysis of its normal operation process. Every time an electrostatic discharge causes an electric field, thus the antenna circuit 1 , acting as a sensor circuit, picks up the field and the discharge itself and sends an enabling signal to the monostable circuit 2. The latter's output presents a known R-C configuration through which the outgoing signal can be gauged according to a time sequence only depending on resistance and capacitance value. In this way the signal of the antenna triggers the monostable 2 which, according to a suitable timing, sends its start signal to the interface circuit 4 which adapts *he received signal to the type of equipment 5 to be interfaced, applying to this equipment 5 a plurality of analog and/or digital signals 4a, 4b, which cutoff the normal operation of the equipment 5 in order to avoid a defective operation. In short, the device 6 acts as a controller of the equipment 5 to which it is fitted by feeding to such equipment signals 4a, 4b, of which at least one disconnects its essential functions, but only in the case of irregular signals generated by an electric field. Immediately after the tracking this disconnection is reset, for example, through a CPU in the equipment 5. It is important that such disconnection takes place only when a disturbance created by an electric field could be sent to the circuits of the equipment 5, so that it does not bring about further operational problems for the operator of the equipment. Therefore, in order to improve the reliability of the device 6, it is suggested to provide also the filter 3, because it filters the disturbances created by the noises of the supply. In this way the invention can achieve the proposed objects. Infact, thanks to this device 6 it is possible to safeguard the operational integrity of any equipment 5 to which 6 is fitted, preventing through a fine filtering of signals any defective and detrimental operation of the equipment 5 owing to an eventual disturbing signal, such as an electrostatic discharge, generated by an electric field. In so far as the illustrated embodiment, an immunity to electrostatic discharges up to 10 KV has been ascertained. Moreover, this device 6 can be easily and cheaply interfaced with any equipment, although it was originally developed to protect the cash registers . Clearly, the invention is not limited to the only embodiment described above, but various modifications and variations are possible, both regarding the parameters and the circuits, all falling within the inventive concept.

Claims: CLAIMS 1 ) Protective device against electrostatic discharges on electronic equipment in general, characterized in that it consists of a combination of knowrt 'ci rcuits including a first antenna circuit to pick up the electr c field created by an electrostatic discharge, which sends an enabling signal, upon sistematic suppression of noises on power line by means of a second circuit, to a third circuit which generates a following start signal with a desired time sequence, so that a fourth interface circuit, enabled by this start signal and ςalvaπically connected to the equipment to be protected, can send to the latter a sequence of monitoring signals which prevent any irregular operation of the equipment itself. 2) Protective device against electrostatic discharges on electronic equipment in general according to claim 1, characterized in that said third circuit consists of a monostable circuit. 3) Protective device against electrostatic discharges on electronic equipment in general according to what previously described and illustrated for the specified objects.

Inventors: ANTONELLI LUIGI, ANTONELLI, LUIGI
Applicants: FACE STANDARD IND, INDUSTRIE FACE STANDARD S.P.A.
Application year: 1987
Main classification: H02H1
IPC codes: H02H1, H05F3